Belt Printer Initial Push (#14385)

# Description Initial push - documentation available at #12998 [How to Download Pull Requests Artifacts for Testing](https://www.orcaslicer.com/wiki/how_to_download_pr_artifacts)
2026-10-19 05:31:04 +00:00 · 2026-06-24 09:42:40 -05:00
commit 34b0d36cda
@@ -0,0 +1,79 @@
+#!/usr/bin/env python3
+"""Belt temperature-tower asset generator (discrete-provini design).
+
+A vertical temperature tower cannot be sliced on a belt printer, so lay a row of
+DISCRETE provini (one per temperature) along the belt (designed Y) with a fixed
+surface gap. Each provino is the chevron+arc unit (belt_temp_provino_unit.stl,
+keel-first); its temperature is ENGRAVED upright into the 50 mm face — a raised
+number would be an unsupported overhang on the belt. The C++ calib_temp belt branch
+(Plater.cpp) injects one M104 per zone 70 layers INTO provino i:
+  print_z[i] = i * PITCH * cos(theta) + 70 * layer_height   (theta = 45)
+inside the body, not in the empty inter-provino gap (which has no sliced layers for
+the event to attach to). PITCH below is the shared geometry contract with that code —
+keep them in sync.
+
+Generates one STL per filament temp range used by Temp_Calibration_Dlg.
+"""
+import numpy as np, trimesh, os
+from matplotlib.textpath import TextPath
+from matplotlib.font_manager import FontProperties
+from shapely.geometry import Polygon as ShPoly
+from shapely.ops import unary_union
+
+HERE = os.path.dirname(os.path.abspath(__file__))
+UNIT = os.path.join(HERE, 'belt_temp_provino_unit.stl')   # single provino, keel-first
+SURF_GAP = 25.0            # surface-to-surface gap between provini (mm) — user spec
+TEXT_H = 9.0
+TEXT_DEPTH = 0.8           # engraving depth (numbers are CUT into the face, not raised:
+                          # a raised number is an unsupported Y-overhang on the belt)
+TEXT_OVERSHOOT = 0.6       # extra height poking out of the face for a clean boolean cut
+
+# Temperature ranges (start, end) per filament family, 5 C step. File name encodes them.
+RANGES = [(230,190),(270,230),(250,230),(280,240),(240,210),(320,280)]
+
+unit = trimesh.load(UNIT)
+dY = unit.bounds[1,1] - unit.bounds[0,1]
+PITCH = dY + SURF_GAP                       # designed-Y pitch == C++ contract constant
+print(f"unit dY={dY:.2f}  PITCH={PITCH:.3f}  (C++ contract: print_z[i]=i*{PITCH:.3f}*cos45)")
+
+# 50 mm face normal (0,-1,1)/sqrt2 ; UPRIGHT basis u=+X det(+1) (verified non-mirrored)
+n = np.array([0,-1,1.])/np.sqrt(2)
+u = np.array([1,0,0.]); v = np.array([0,1,1.])/np.sqrt(2)
+R = np.column_stack([u,v,n])
+fn = unit.face_normals; fc = unit.triangles_center; fa = unit.area_faces
+sel = (fn@n) > 0.9
+face_c = (fc[sel]*fa[sel,None]).sum(0)/fa[sel].sum()
+
+def text_mesh(s):
+    tp = TextPath((0,0), s, size=TEXT_H, prop=FontProperties(family='DejaVu Sans'))
+    rings = [ShPoly(p) for p in tp.to_polygons() if len(p)>=3]
+    rings.sort(key=lambda r:r.area, reverse=True)
+    used=[False]*len(rings); parts=[]
+    for i,o in enumerate(rings):
+        if used[i]: continue
+        holes=[]
+        for j in range(i+1,len(rings)):
+            if not used[j] and o.contains(rings[j]): holes.append(rings[j].exterior.coords); used[j]=True
+        parts.append(ShPoly(o.exterior.coords,holes)); used[i]=True
+    poly = unary_union(parts)
+    geoms = list(poly.geoms) if poly.geom_type=='MultiPolygon' else [poly]
+    m = trimesh.util.concatenate([trimesh.creation.extrude_polygon(g,height=TEXT_DEPTH+TEXT_OVERSHOOT) for g in geoms])
+    c = m.bounds.mean(axis=0); m.apply_translation([-c[0],-c[1],0]); return m
+
+for t_start, t_end in RANGES:
+    temps = list(range(t_start, t_end-1, -5))
+    parts=[]
+    for i,T in enumerate(temps):
+        c = unit.copy(); c.apply_translation([0, i*PITCH, 0])
+        t = text_mesh(str(T)); M=np.eye(4); M[:3,:3]=R; t.apply_transform(M)
+        # place the text spanning from TEXT_DEPTH inside the face to TEXT_OVERSHOOT outside,
+        # then CUT it out of the provino (engrave) — no raised material, no Y-overhang.
+        t.apply_translation(face_c - n*TEXT_DEPTH + np.array([0,i*PITCH,0]))
+        c = trimesh.boolean.difference([c, t], engine='manifold')
+        parts.append(c)
+    asset = trimesh.util.concatenate(parts)
+    out = os.path.join(HERE, f"belt_temp_tower_{t_start}_{t_end}.stl")
+    asset.export(out)
+    dims = np.round(asset.bounds[1]-asset.bounds[0],1)
+    wt = all(p.is_watertight for p in parts)
+    print(f"  {t_start}->{t_end}: {len(temps)} zones  bbox={dims}  watertight={wt}  -> {os.path.basename(out)}")
@@ -1,9 +1,13 @@
 {
 	"name": "Custom Printer",
-	"version": "02.04.00.00",
+	"version": "02.04.00.03",
 	"force_update": "0",
 	"description": "My configurations",
 	"machine_model_list": [
+		{
+			"name": "Generic Belt Printer",
+			"sub_path": "machine/MyBeltPrinter.json"
+		},
 		{
 			"name": "Generic Klipper Printer",
 			"sub_path": "machine/MyKlipper.json"
@@ -262,18 +266,38 @@
 			"name": "MyKlipper 0.8 nozzle",
 			"sub_path": "machine/MyKlipper 0.8 nozzle.json"
 		},
+		{
+			"name": "fdm_belt_common",
+			"sub_path": "machine/fdm_belt_common.json"
+		},
 		{
 			"name": "fdm_toolchanger_common",
 			"sub_path": "machine/fdm_toolchanger_common.json"
 		},
-		{
-			"name": "MyRepetier 0.4 nozzle",
-			"sub_path": "machine/MyRepetier 0.4 nozzle.json"
-		},
 		{
 			"name": "MyRRF 0.4 nozzle",
 			"sub_path": "machine/MyRRF 0.4 nozzle.json"
 		},
+		{
+			"name": "MyBeltPrinter 0.2 nozzle",
+			"sub_path": "machine/MyBeltPrinter 0.2 nozzle.json"
+		},
+		{
+			"name": "MyBeltPrinter 0.4 nozzle",
+			"sub_path": "machine/MyBeltPrinter 0.4 nozzle.json"
+		},
+		{
+			"name": "MyBeltPrinter 0.6 nozzle",
+			"sub_path": "machine/MyBeltPrinter 0.6 nozzle.json"
+		},
+		{
+			"name": "MyBeltPrinter 0.8 nozzle",
+			"sub_path": "machine/MyBeltPrinter 0.8 nozzle.json"
+		},
+		{
+			"name": "MyRepetier 0.4 nozzle",
+			"sub_path": "machine/MyRepetier 0.4 nozzle.json"
+		},
 		{
 			"name": "MyToolChanger 0.2 nozzle",
 			"sub_path": "machine/MyToolChanger 0.2 nozzle.json"
@@ -0,0 +1,26 @@
+{
+	"type": "machine",
+	"name": "MyBeltPrinter 0.2 nozzle",
+	"inherits": "fdm_belt_common",
+	"from": "system",
+	"setting_id": "GM_BELT_001",
+	"instantiation": "true",
+	"printer_model": "Generic Belt Printer",
+	"nozzle_diameter": [
+		"0.2"
+	],
+	"max_layer_height": [
+		"0.16"
+	],
+	"min_layer_height": [
+		"0.04"
+	],
+	"printer_variant": "0.2",
+	"printable_area": [
+		"0x0",
+		"350x0",
+		"350x350",
+		"0x350"
+	],
+	"printable_height": "300"
+}
@@ -0,0 +1,20 @@
+{
+	"type": "machine",
+	"name": "MyBeltPrinter 0.4 nozzle",
+	"inherits": "fdm_belt_common",
+	"from": "system",
+	"setting_id": "GM_BELT_002",
+	"instantiation": "true",
+	"printer_model": "Generic Belt Printer",
+	"nozzle_diameter": [
+		"0.4"
+	],
+	"printer_variant": "0.4",
+	"printable_area": [
+		"0x0",
+		"350x0",
+		"350x350",
+		"0x350"
+	],
+	"printable_height": "300"
+}
@@ -0,0 +1,26 @@
+{
+	"type": "machine",
+	"name": "MyBeltPrinter 0.6 nozzle",
+	"inherits": "fdm_belt_common",
+	"from": "system",
+	"setting_id": "GM_BELT_003",
+	"instantiation": "true",
+	"printer_model": "Generic Belt Printer",
+	"nozzle_diameter": [
+		"0.6"
+	],
+	"max_layer_height": [
+		"0.4"
+	],
+	"min_layer_height": [
+		"0.12"
+	],
+	"printer_variant": "0.6",
+	"printable_area": [
+		"0x0",
+		"350x0",
+		"350x350",
+		"0x350"
+	],
+	"printable_height": "300"
+}
@@ -0,0 +1,26 @@
+{
+	"type": "machine",
+	"name": "MyBeltPrinter 0.8 nozzle",
+	"inherits": "fdm_belt_common",
+	"from": "system",
+	"setting_id": "GM_BELT_004",
+	"instantiation": "true",
+	"printer_model": "Generic Belt Printer",
+	"nozzle_diameter": [
+		"0.8"
+	],
+	"max_layer_height": [
+		"0.6"
+	],
+	"min_layer_height": [
+		"0.2"
+	],
+	"printer_variant": "0.8",
+	"printable_area": [
+		"0x0",
+		"350x0",
+		"350x350",
+		"0x350"
+	],
+	"printable_height": "300"
+}
@@ -0,0 +1,12 @@
+{
+	"type": "machine_model",
+	"name": "Generic Belt Printer",
+	"model_id": "my_belt_01",
+	"nozzle_diameter": "0.4;0.2;0.6;0.8",
+	"machine_tech": "FFF",
+	"family": "MyPrinter",
+	"bed_model": "Custom_350_bed.stl",
+	"bed_texture": "orcaslicer_bed_texture.svg",
+	"hotend_model": "",
+	"default_materials": "Generic PLA @System;Generic PLA-CF @System;Generic PETG @System;Generic TPU @System;Generic PC @System;Generic PVA @System;Generic PA @System;Generic PA-CF @System"
+}
@@ -0,0 +1,99 @@
+{
+	"type": "machine",
+	"name": "fdm_belt_common",
+	"inherits": "fdm_klipper_common",
+	"from": "system",
+	"instantiation": "false",
+	"gcode_flavor": "klipper",
+	"single_extruder_multi_material": "0",
+	"default_filament_profile": [
+		"Generic PLA @System"
+	],
+	"default_print_profile": "0.20mm Standard @System",
+	"max_layer_height": [
+		"0.32"
+	],
+	"min_layer_height": [
+		"0.08"
+	],
+	"deretraction_speed": [
+		"30"
+	],
+	"extruder_colour": [
+		"#FCE94F"
+	],
+	"extruder_offset": [
+		"0x0"
+	],
+	"long_retractions_when_cut": [
+		"0"
+	],
+	"nozzle_diameter": [
+		"0.4"
+	],
+	"retract_before_wipe": [
+		"70%"
+	],
+	"retract_length_toolchange": [
+		"2"
+	],
+	"retract_lift_above": [
+		"0"
+	],
+	"retract_lift_below": [
+		"0"
+	],
+	"retract_lift_enforce": [
+		"All Surfaces"
+	],
+	"retract_restart_extra": [
+		"0"
+	],
+	"retract_restart_extra_toolchange": [
+		"0"
+	],
+	"retract_when_changing_layer": [
+		"1"
+	],
+	"retraction_distances_when_cut": [
+		"18"
+	],
+	"retraction_length": [
+		"0.8"
+	],
+	"retraction_minimum_travel": [
+		"1"
+	],
+	"retraction_speed": [
+		"30"
+	],
+	"travel_slope": [
+		"3"
+	],
+	"wipe": [
+		"1"
+	],
+	"wipe_distance": [
+		"1"
+	],
+	"z_hop": [
+		"0.4"
+	],
+	"z_hop_types": [
+		"Normal Lift"
+	],
+	"gcode_remap_x": "rev_x",
+	"gcode_remap_y": "pos_z",
+	"gcode_remap_z": "pos_y",
+	"printer_extruder_id": [
+		"1"
+	],
+	"belt_printer": "1",
+	"belt_slice_rotation": "x",
+	"belt_slice_rotation_angle": "45",
+	"belt_slice_rotation_global": "1",
+	"build_plate_tilt_x": "45",
+	"purge_in_prime_tower": "0",
+	"scan_first_layer": "0",
+	"auxiliary_fan": "0"
+}
@@ -0,0 +1,54 @@
+{
+    "name": "IdeaFormer",
+    "version": "02.00.00.02",
+    "force_update": "0",
+    "description": "IdeaFormer belt printer configurations",
+    "machine_model_list": [
+        {
+            "name": "IdeaFormer IR3 V2",
+            "sub_path": "machine/IdeaFormer IR3 V2.json"
+        }
+    ],
+    "process_list": [
+        {
+            "name": "fdm_process_common",
+            "sub_path": "process/fdm_process_common.json"
+        },
+        {
+            "name": "0.20mm Standard @IdeaFormer IR3 V2",
+            "sub_path": "process/0.20mm Standard @IdeaFormer IR3 V2.json"
+        }
+    ],
+    "filament_list": [
+        {
+            "name": "Generic PLA @IdeaFormer IR3 V2",
+            "sub_path": "filament/Generic PLA @IdeaFormer IR3 V2.json"
+        },
+        {
+            "name": "eSUN PLA @IdeaFormer IR3 V2",
+            "sub_path": "filament/eSUN PLA @IdeaFormer IR3 V2.json"
+        },
+        {
+            "name": "Generic PETG @IdeaFormer IR3 V2",
+            "sub_path": "filament/Generic PETG @IdeaFormer IR3 V2.json"
+        }
+    ],
+    "machine_list": [
+        {
+            "name": "fdm_machine_common",
+            "sub_path": "machine/fdm_machine_common.json"
+        },
+        {
+            "name": "fdm_klipper_common",
+            "sub_path": "machine/fdm_klipper_common.json"
+        },
+        {
+            "name": "fdm_belt_common",
+            "sub_path": "machine/fdm_belt_common.json"
+        },
+        {
+            "name": "IdeaFormer IR3 V2 0.4 nozzle",
+            "sub_path": "machine/IdeaFormer IR3 V2 0.4 nozzle.json"
+        }
+    ]
+}
@@ -0,0 +1,112 @@
+{
+	"type": "filament",
+	"name": "Generic PETG @IdeaFormer IR3 V2",
+	"inherits": "Generic PETG @System",
+	"from": "system",
+	"instantiation": "true",
+	"compatible_printers": [
+		"IdeaFormer IR3 V2 0.4 nozzle"
+	],
+	"filament_type": [
+		"PETG"
+	],
+	"filament_vendor": [
+		"Generic"
+	],
+	"filament_settings_id": [
+		"Generic PETG @IdeaFormer IR3 V2"
+	],
+	"filament_diameter": [
+		"1.75"
+	],
+	"filament_density": [
+		"1.27"
+	],
+	"filament_flow_ratio": [
+		"0.95"
+	],
+	"filament_cost": [
+		"25"
+	],
+	"filament_max_volumetric_speed": [
+		"10"
+	],
+	"nozzle_temperature": [
+		"240"
+	],
+	"nozzle_temperature_initial_layer": [
+		"245"
+	],
+	"nozzle_temperature_range_low": [
+		"220"
+	],
+	"nozzle_temperature_range_high": [
+		"260"
+	],
+	"temperature_vitrification": [
+		"70"
+	],
+	"hot_plate_temp": [
+		"80"
+	],
+	"hot_plate_temp_initial_layer": [
+		"80"
+	],
+	"cool_plate_temp": [
+		"80"
+	],
+	"cool_plate_temp_initial_layer": [
+		"80"
+	],
+	"textured_plate_temp": [
+		"80"
+	],
+	"textured_plate_temp_initial_layer": [
+		"80"
+	],
+	"fan_min_speed": [
+		"40"
+	],
+	"fan_max_speed": [
+		"60"
+	],
+	"overhang_fan_threshold": [
+		"25%"
+	],
+	"overhang_fan_speed": [
+		"80"
+	],
+	"close_fan_the_first_x_layers": [
+		"3"
+	],
+	"full_fan_speed_layer": [
+		"8"
+	],
+	"slow_down_min_speed": [
+		"20"
+	],
+	"slow_down_layer_time": [
+		"4"
+	],
+	"fan_cooling_layer_time": [
+		"100"
+	],
+	"reduce_fan_stop_start_freq": [
+		"1"
+	],
+	"filament_retraction_length": [
+		"2"
+	],
+	"filament_retraction_speed": [
+		"40"
+	],
+	"filament_deretraction_speed": [
+		"40"
+	],
+	"filament_z_hop": [
+		"0.4"
+	],
+	"filament_start_gcode": [
+		"; Generic PETG @IdeaFormer IR3 V2 — belt PETG, bed 80C"
+	]
+}
@@ -0,0 +1,112 @@
+{
+	"type": "filament",
+	"name": "Generic PLA @IdeaFormer IR3 V2",
+	"inherits": "Generic PLA @System",
+	"from": "system",
+	"instantiation": "true",
+	"compatible_printers": [
+		"IdeaFormer IR3 V2 0.4 nozzle"
+	],
+	"filament_type": [
+		"PLA"
+	],
+	"filament_vendor": [
+		"Generic"
+	],
+	"filament_settings_id": [
+		"Generic PLA @IdeaFormer IR3 V2"
+	],
+	"filament_diameter": [
+		"1.75"
+	],
+	"filament_density": [
+		"1.24"
+	],
+	"filament_flow_ratio": [
+		"0.98"
+	],
+	"filament_cost": [
+		"20"
+	],
+	"filament_max_volumetric_speed": [
+		"12"
+	],
+	"nozzle_temperature": [
+		"215"
+	],
+	"nozzle_temperature_initial_layer": [
+		"220"
+	],
+	"nozzle_temperature_range_low": [
+		"190"
+	],
+	"nozzle_temperature_range_high": [
+		"240"
+	],
+	"temperature_vitrification": [
+		"45"
+	],
+	"hot_plate_temp": [
+		"75"
+	],
+	"hot_plate_temp_initial_layer": [
+		"75"
+	],
+	"cool_plate_temp": [
+		"75"
+	],
+	"cool_plate_temp_initial_layer": [
+		"75"
+	],
+	"textured_plate_temp": [
+		"75"
+	],
+	"textured_plate_temp_initial_layer": [
+		"75"
+	],
+	"fan_min_speed": [
+		"100"
+	],
+	"fan_max_speed": [
+		"100"
+	],
+	"overhang_fan_threshold": [
+		"50%"
+	],
+	"overhang_fan_speed": [
+		"100"
+	],
+	"close_fan_the_first_x_layers": [
+		"3"
+	],
+	"full_fan_speed_layer": [
+		"8"
+	],
+	"slow_down_min_speed": [
+		"20"
+	],
+	"slow_down_layer_time": [
+		"4"
+	],
+	"fan_cooling_layer_time": [
+		"100"
+	],
+	"reduce_fan_stop_start_freq": [
+		"1"
+	],
+	"filament_retraction_length": [
+		"1.5"
+	],
+	"filament_retraction_speed": [
+		"35"
+	],
+	"filament_deretraction_speed": [
+		"30"
+	],
+	"filament_z_hop": [
+		"0.4"
+	],
+	"filament_start_gcode": [
+		"; Generic PLA @IdeaFormer IR3 V2 — belt PLA, bed 75C"
+	]
+}
@@ -0,0 +1,34 @@
+{
+	"type": "filament",
+	"name": "eSUN PLA @IdeaFormer IR3 V2",
+	"inherits": "Generic PLA @IdeaFormer IR3 V2",
+	"from": "system",
+	"instantiation": "true",
+	"compatible_printers": [
+		"IdeaFormer IR3 V2 0.4 nozzle"
+	],
+	"filament_type": [
+		"PLA"
+	],
+	"filament_vendor": [
+		"eSUN"
+	],
+	"filament_settings_id": [
+		"eSUN PLA @IdeaFormer IR3 V2"
+	],
+	"nozzle_temperature_initial_layer": [
+		"200"
+	],
+	"nozzle_temperature": [
+		"200"
+	],
+	"enable_pressure_advance": [
+		"1"
+	],
+	"pressure_advance": [
+		"0.12"
+	],
+	"filament_max_volumetric_speed": [
+		"20"
+	]
+}
@@ -0,0 +1,94 @@
+{
+	"type": "machine",
+	"name": "IdeaFormer IR3 V2 0.4 nozzle",
+	"inherits": "fdm_belt_common",
+	"from": "system",
+	"setting_id": "GMIF001",
+	"instantiation": "true",
+	"printer_model": "IdeaFormer IR3 V2",
+	"printer_variant": "0.4",
+	"nozzle_diameter": [
+		"0.4"
+	],
+	"printable_area": [
+		"0x0",
+		"250x0",
+		"250x2000",
+		"0x2000"
+	],
+	"printable_height": "250",
+	"belt_printer_infinite_y": "1",
+	"thumbnails": [
+		"48x48/PNG",
+		"300x300/PNG"
+	],
+	"default_filament_profile": [
+		"Generic PLA @IdeaFormer IR3 V2"
+	],
+	"default_print_profile": "0.20mm Standard @IdeaFormer IR3 V2",
+	"use_relative_e_distances": "1",
+	"machine_max_acceleration_e": [
+		"5000"
+	],
+	"machine_max_acceleration_extruding": [
+		"5000"
+	],
+	"machine_max_acceleration_retracting": [
+		"1000"
+	],
+	"machine_max_acceleration_travel": [
+		"9000"
+	],
+	"machine_max_acceleration_x": [
+		"5000"
+	],
+	"machine_max_acceleration_y": [
+		"5000"
+	],
+	"machine_max_acceleration_z": [
+		"100"
+	],
+	"machine_max_jerk_e": [
+		"2.5"
+	],
+	"machine_max_jerk_x": [
+		"10"
+	],
+	"machine_max_jerk_y": [
+		"10"
+	],
+	"machine_max_jerk_z": [
+		"0.4"
+	],
+	"machine_max_speed_e": [
+		"60"
+	],
+	"machine_max_speed_x": [
+		"500"
+	],
+	"machine_max_speed_y": [
+		"500"
+	],
+	"machine_max_speed_z": [
+		"20"
+	],
+	"retraction_length": [
+		"2"
+	],
+	"retraction_speed": [
+		"40"
+	],
+	"deretraction_speed": [
+		"40"
+	],
+	"z_hop": [
+		"0.4"
+	],
+	"retract_lift_below": [
+		"300"
+	],
+	"machine_start_gcode": "; === IdeaFormer IR3 V2 Belt Printer Start ===\n; Axes: X=lateral, Y=gantry height (probe), Z=belt\nG90 ; absolute positioning\nM82 ; absolute extruder\nG21 ; millimeters\nG28 ; home all axes\nG1 Y20 F500 ; lift nozzle 20mm from belt\n; Bed + hotend temps come from the active filament profile. Belt PLA requires 75 C bed — use Generic/eSun PLA @IdeaFormer IR3 V2 filament presets to get it automatically.\nM140 S[hot_plate_temp_initial_layer] ; set bed temp\nM104 S[nozzle_temperature_initial_layer] ; hotend temp\nM109 S[nozzle_temperature_initial_layer] ; wait hotend\nM190 S[hot_plate_temp_initial_layer] ; wait bed\n; --- Purge blob ---\nG92 E0 ; zero extruder\nG1 Y.1 ; nozzle 0.1mm above belt\nG1 E15 F1000 ; purge 15mm blob\nG1 Z20 E25 F800 ; belt advance 20mm + extrude\nG1 E23 ; retract 2mm\nG28 Y ; re-probe belt surface\nG1 E25 ; de-retract\n; --- Prime lines (full 250mm bed width) ---\nFMS_on ; filament motion sensor\nG1 X250 E50 F2000 ; prime line 1\nG92 Z0 ; reset belt origin\nG1 Z.4 ; belt advance 0.4mm\nG1 X0 E75 ; prime line 2\nG1 F1000 ; default feedrate\nG92 E0 Z0 ; zero extruder + belt = print origin\n",
+	"machine_end_gcode": "; === IdeaFormer IR3 V2 Belt Printer End ===\nM400 ; wait for moves to finish\nM104 S0 ; heater off\nM140 S0 ; bed off\nG92 E0 ; zero extruder\nG1 E-5 F300 ; retract 5mm\nG4 P5000 ; wait for ooze\nG91 ; relative mode - keep every end move relative on a belt\nG1 Y20 F1000 ; raise gantry 20mm for clearance over the part\nG1 Z676 F3000 ; advance belt one full machine-depth to eject the part and clean the belt\nG90 ; back to absolute\nG28 X ; home X only - NEVER 'G28' all: that homes Z/belt and reverses the whole print back into the gantry\nFMS_off ; filament motion sensor off\nBED_MESH_CLEAR\nM84 ; disable motors\n",
+	"machine_pause_gcode": "PAUSE",
+	"layer_change_gcode": "G92 E0 ; belt: reset extruder at layer change (relative E)"
+}
@@ -0,0 +1,12 @@
+{
+	"type": "machine_model",
+	"name": "IdeaFormer IR3 V2",
+	"model_id": "IdeaFormer_IR3_V2",
+	"nozzle_diameter": "0.4",
+	"machine_tech": "FFF",
+	"family": "IdeaFormer",
+	"bed_model": "",
+	"bed_texture": "",
+	"hotend_model": "",
+	"default_materials": "Generic PLA @IdeaFormer IR3 V2;Generic PETG @IdeaFormer IR3 V2"
+}
@@ -0,0 +1,99 @@
+{
+	"type": "machine",
+	"name": "fdm_belt_common",
+	"inherits": "fdm_klipper_common",
+	"from": "system",
+	"instantiation": "false",
+	"gcode_flavor": "klipper",
+	"single_extruder_multi_material": "0",
+	"default_filament_profile": [
+		"Generic PLA @System"
+	],
+	"default_print_profile": "0.20mm Standard @System",
+	"max_layer_height": [
+		"0.32"
+	],
+	"min_layer_height": [
+		"0.08"
+	],
+	"deretraction_speed": [
+		"30"
+	],
+	"extruder_colour": [
+		"#FCE94F"
+	],
+	"extruder_offset": [
+		"0x0"
+	],
+	"long_retractions_when_cut": [
+		"0"
+	],
+	"nozzle_diameter": [
+		"0.4"
+	],
+	"retract_before_wipe": [
+		"70%"
+	],
+	"retract_length_toolchange": [
+		"2"
+	],
+	"retract_lift_above": [
+		"0"
+	],
+	"retract_lift_below": [
+		"0"
+	],
+	"retract_lift_enforce": [
+		"All Surfaces"
+	],
+	"retract_restart_extra": [
+		"0"
+	],
+	"retract_restart_extra_toolchange": [
+		"0"
+	],
+	"retract_when_changing_layer": [
+		"1"
+	],
+	"retraction_distances_when_cut": [
+		"18"
+	],
+	"retraction_length": [
+		"0.8"
+	],
+	"retraction_minimum_travel": [
+		"1"
+	],
+	"retraction_speed": [
+		"30"
+	],
+	"travel_slope": [
+		"3"
+	],
+	"wipe": [
+		"1"
+	],
+	"wipe_distance": [
+		"1"
+	],
+	"z_hop": [
+		"0.4"
+	],
+	"z_hop_types": [
+		"Normal Lift"
+	],
+	"gcode_remap_x": "rev_x",
+	"gcode_remap_y": "pos_z",
+	"gcode_remap_z": "pos_y",
+	"printer_extruder_id": [
+		"1"
+	],
+	"belt_printer": "1",
+	"belt_slice_rotation": "x",
+	"belt_slice_rotation_angle": "45",
+	"belt_slice_rotation_global": "1",
+	"build_plate_tilt_x": "45",
+	"purge_in_prime_tower": "0",
+	"scan_first_layer": "0",
+	"auxiliary_fan": "0"
+}
@@ -0,0 +1,141 @@
+{
+	"type": "machine",
+	"name": "fdm_klipper_common",
+	"inherits": "fdm_machine_common",
+	"from": "system",
+	"instantiation": "false",
+	"gcode_flavor": "klipper",
+	"machine_max_acceleration_e": [
+		"5000",
+		"5000"
+	],
+	"machine_max_acceleration_extruding": [
+		"20000",
+		"20000"
+	],
+	"machine_max_acceleration_retracting": [
+		"5000",
+		"5000"
+	],
+	"machine_max_acceleration_travel": [
+		"20000",
+		"20000"
+	],
+	"machine_max_acceleration_x": [
+		"20000",
+		"20000"
+	],
+	"machine_max_acceleration_y": [
+		"20000",
+		"20000"
+	],
+	"machine_max_acceleration_z": [
+		"500",
+		"200"
+	],
+	"machine_max_speed_e": [
+		"25",
+		"25"
+	],
+	"machine_max_speed_x": [
+		"500",
+		"200"
+	],
+	"machine_max_speed_y": [
+		"500",
+		"200"
+	],
+	"machine_max_speed_z": [
+		"12",
+		"12"
+	],
+	"machine_max_jerk_e": [
+		"2.5",
+		"2.5"
+	],
+	"machine_max_jerk_x": [
+		"9",
+		"9"
+	],
+	"machine_max_jerk_y": [
+		"9",
+		"9"
+	],
+	"machine_max_jerk_z": [
+		"0.2",
+		"0.4"
+	],
+	"machine_min_extruding_rate": [
+		"0",
+		"0"
+	],
+	"machine_min_travel_rate": [
+		"0",
+		"0"
+	],
+	"max_layer_height": [
+		"0.32"
+	],
+	"min_layer_height": [
+		"0.08"
+	],
+	"printable_height": "250",
+	"extruder_clearance_radius": "65",
+	"extruder_clearance_height_to_rod": "36",
+	"extruder_clearance_height_to_lid": "140",
+	"printer_settings_id": "",
+	"printer_technology": "FFF",
+	"printer_variant": "0.4",
+	"retraction_minimum_travel": [
+		"1"
+	],
+	"retract_before_wipe": [
+		"70%"
+	],
+	"retract_when_changing_layer": [
+		"1"
+	],
+	"retraction_length": [
+		"0.8"
+	],
+	"retract_length_toolchange": [
+		"2"
+	],
+	"z_hop": [
+		"0.4"
+	],
+	"retract_restart_extra": [
+		"0"
+	],
+	"retract_restart_extra_toolchange": [
+		"0"
+	],
+	"retraction_speed": [
+		"30"
+	],
+	"deretraction_speed": [
+		"30"
+	],
+	"z_hop_types": "Normal Lift",
+	"silent_mode": "0",
+	"single_extruder_multi_material": "1",
+	"change_filament_gcode": "",
+	"wipe": [
+		"1"
+	],
+	"default_filament_profile": [
+		"Generic PLA @System"
+	],
+	"default_print_profile": "0.20mm Standard @MyKlipper",
+	"bed_exclude_area": [
+		"0x0"
+	],
+	"machine_start_gcode": "M190 S[bed_temperature_initial_layer_single]\nM109 S[nozzle_temperature_initial_layer]\nPRINT_START EXTRUDER=[nozzle_temperature_initial_layer] BED=[bed_temperature_initial_layer_single]\n",
+	"machine_end_gcode": "PRINT_END",
+	"layer_change_gcode": ";AFTER_LAYER_CHANGE\n;[layer_z]",
+	"before_layer_change_gcode": ";BEFORE_LAYER_CHANGE\n;[layer_z]\nG92 E0\n",
+	"machine_pause_gcode": "PAUSE",
+	"scan_first_layer": "0",
+	"nozzle_type": "undefine",
+	"auxiliary_fan": "0"
+}
@@ -0,0 +1,119 @@
+{
+	"type": "machine",
+	"name": "fdm_machine_common",
+	"from": "system",
+	"instantiation": "false",
+	"printer_technology": "FFF",
+	"deretraction_speed": [
+		"40"
+	],
+	"extruder_colour": [
+		"#FCE94F"
+	],
+	"extruder_offset": [
+		"0x0"
+	],
+	"gcode_flavor": "marlin",
+	"silent_mode": "0",
+	"machine_max_acceleration_e": [
+		"5000"
+	],
+	"machine_max_acceleration_extruding": [
+		"10000"
+	],
+	"machine_max_acceleration_retracting": [
+		"1000"
+	],
+	"machine_max_acceleration_x": [
+		"10000"
+	],
+	"machine_max_acceleration_y": [
+		"10000"
+	],
+	"machine_max_acceleration_z": [
+		"500"
+	],
+	"machine_max_speed_e": [
+		"60"
+	],
+	"machine_max_speed_x": [
+		"500"
+	],
+	"machine_max_speed_y": [
+		"500"
+	],
+	"machine_max_speed_z": [
+		"10"
+	],
+	"machine_max_jerk_e": [
+		"5"
+	],
+	"machine_max_jerk_x": [
+		"8"
+	],
+	"machine_max_jerk_y": [
+		"8"
+	],
+	"machine_max_jerk_z": [
+		"0.4"
+	],
+	"machine_min_extruding_rate": [
+		"0"
+	],
+	"machine_min_travel_rate": [
+		"0"
+	],
+	"max_layer_height": [
+		"0.32"
+	],
+	"min_layer_height": [
+		"0.08"
+	],
+	"printable_height": "250",
+	"extruder_clearance_radius": "65",
+	"extruder_clearance_height_to_rod": "36",
+	"extruder_clearance_height_to_lid": "140",
+	"nozzle_diameter": [
+		"0.4"
+	],
+	"printer_settings_id": "",
+	"printer_variant": "0.4",
+	"retraction_minimum_travel": [
+		"2"
+	],
+	"retract_before_wipe": [
+		"70%"
+	],
+	"retract_when_changing_layer": [
+		"1"
+	],
+	"retraction_length": [
+		"1"
+	],
+	"retract_length_toolchange": [
+		"1"
+	],
+	"z_hop": [
+		"0"
+	],
+	"retract_restart_extra": [
+		"0"
+	],
+	"retract_restart_extra_toolchange": [
+		"0"
+	],
+	"retraction_speed": [
+		"60"
+	],
+	"single_extruder_multi_material": "1",
+	"change_filament_gcode": "",
+	"wipe": [
+		"1"
+	],
+	"default_print_profile": "",
+	"machine_start_gcode": "G0 Z20 F9000\nG92 E0; G1 E-10 F1200\nG28\nM970 Q1 A10 B10 C130 K0\nM970 Q1 A10 B131 C250 K1\nM974 Q1 S1 P0\nM970 Q0 A10 B10 C130 H20 K0\nM970 Q0 A10 B131 C250 K1\nM974 Q0 S1 P0\nM220 S100 ;Reset Feedrate\nM221 S100 ;Reset Flowrate\nG29 ;Home\nG90;\nG92 E0 ;Reset Extruder \nG1 Z2.0 F3000 ;Move Z Axis up \nG1 X10.1 Y20 Z0.28 F5000.0 ;Move to start position\nM109 S205;\nG1 X10.1 Y200.0 Z0.28 F1500.0 E15 ;Draw the first line\nG1 X10.4 Y200.0 Z0.28 F5000.0 ;Move to side a little\nG1 X10.4 Y20 Z0.28 F1500.0 E30 ;Draw the second line\nG92 E0 ;Reset Extruder \nG1 X110 Y110 Z2.0 F3000 ;Move Z Axis up",
+	"machine_end_gcode": "M400 ; wait for buffer to clear\nG92 E0 ; zero the extruder\nG1 E-4.0 F3600; retract \nG91\nG1 Z3;\nM104 S0 ; turn off hotend\nM140 S0 ; turn off bed\nM106 S0 ; turn off fan\nG90 \nG0 X110 Y200 F3600 \nprint_end",
+	"layer_change_gcode": ";AFTER_LAYER_CHANGE\n;[layer_z]",
+	"before_layer_change_gcode": ";BEFORE_LAYER_CHANGE\n;[layer_z]\nG92 E0\n",
+	"machine_pause_gcode": "M601"
+}
@@ -0,0 +1,22 @@
+{
+	"type": "process",
+	"name": "0.20mm Standard @IdeaFormer IR3 V2",
+	"inherits": "fdm_process_common",
+	"from": "system",
+	"instantiation": "true",
+	"layer_height": "0.2",
+	"initial_layer_print_height": "0.2",
+	"initial_layer_line_width": "0.42",
+	"wall_loops": "2",
+	"reduce_infill_retraction": "1",
+	"detect_overhang_wall": "1",
+	"skirt_loops": "0",
+	"skirt_distance": "0",
+	"sparse_infill_pattern": "grid",
+	"sparse_infill_speed": "200",
+	"support_base_pattern": "rectilinear",
+	"support_interface_pattern": "rectilinear",
+	"compatible_printers": [
+		"IdeaFormer IR3 V2 0.4 nozzle"
+	]
+}
@@ -0,0 +1,108 @@
+{
+	"type": "process",
+	"name": "fdm_process_common",
+	"from": "system",
+	"instantiation": "false",
+	"adaptive_layer_height": "0",
+	"reduce_crossing_wall": "0",
+	"max_travel_detour_distance": "0",
+	"bottom_surface_pattern": "monotonic",
+	"bottom_shell_thickness": "0",
+	"bridge_speed": "50",
+	"brim_width": "5",
+	"brim_object_gap": "0.1",
+	"compatible_printers": [],
+	"compatible_printers_condition": "",
+	"print_sequence": "by layer",
+	"default_acceleration": "1000",
+	"initial_layer_acceleration": "500",
+	"top_surface_acceleration": "1000",
+	"travel_acceleration": "1000",
+	"inner_wall_acceleration": "1000",
+	"outer_wall_acceleration": "700",
+	"bridge_no_support": "0",
+	"draft_shield": "disabled",
+	"elefant_foot_compensation": "0",
+	"enable_arc_fitting": "0",
+	"wall_infill_order": "inner wall/outer wall/infill",
+	"infill_direction": "45",
+	"sparse_infill_density": "15%",
+	"sparse_infill_pattern": "crosshatch",
+	"initial_layer_print_height": "0.2",
+	"infill_combination": "0",
+	"infill_wall_overlap": "25%",
+	"interface_shells": "0",
+	"ironing_flow": "10%",
+	"ironing_spacing": "0.15",
+	"ironing_speed": "30",
+	"ironing_type": "no ironing",
+	"reduce_infill_retraction": "1",
+	"filename_format": "{input_filename_base}_{layer_height}mm_{filament_type[initial_tool]}_{printer_model}_{print_time}.gcode",
+	"detect_overhang_wall": "1",
+	"slowdown_for_curled_perimeters": "1",
+	"overhang_1_4_speed": "0",
+	"overhang_2_4_speed": "50",
+	"overhang_3_4_speed": "30",
+	"overhang_4_4_speed": "10",
+	"line_width": "110%",
+	"inner_wall_line_width": "110%",
+	"outer_wall_line_width": "100%",
+	"top_surface_line_width": "93.75%",
+	"sparse_infill_line_width": "110%",
+	"initial_layer_line_width": "120%",
+	"internal_solid_infill_line_width": "120%",
+	"support_line_width": "96%",
+	"wall_loops": "3",
+	"print_settings_id": "",
+	"raft_layers": "0",
+	"seam_position": "aligned",
+	"skirt_distance": "2",
+	"skirt_height": "3",
+	"min_skirt_length": "4",
+	"skirt_loops": "0",
+	"minimum_sparse_infill_area": "15",
+	"spiral_mode": "0",
+	"standby_temperature_delta": "-5",
+	"enable_support": "0",
+	"resolution": "0.012",
+	"support_type": "normal(auto)",
+	"support_on_build_plate_only": "0",
+	"support_top_z_distance": "0.2",
+	"support_bottom_z_distance": "0.2",
+	"support_filament": "0",
+	"support_interface_loop_pattern": "0",
+	"support_interface_filament": "0",
+	"support_interface_top_layers": "2",
+	"support_interface_bottom_layers": "2",
+	"support_interface_spacing": "0.5",
+	"support_interface_speed": "80",
+	"support_base_pattern": "default",
+	"support_base_pattern_spacing": "2.5",
+	"support_speed": "150",
+	"support_threshold_angle": "30",
+	"support_object_xy_distance": "0.35",
+	"tree_support_branch_angle": "30",
+	"tree_support_wall_count": "0",
+	"tree_support_with_infill": "0",
+	"detect_thin_wall": "0",
+	"top_surface_pattern": "monotonicline",
+	"top_shell_thickness": "0.8",
+	"enable_prime_tower": "1",
+	"wipe_tower_no_sparse_layers": "0",
+	"prime_tower_width": "60",
+	"xy_hole_compensation": "0",
+	"xy_contour_compensation": "0",
+	"layer_height": "0.2",
+	"bottom_shell_layers": "3",
+	"top_shell_layers": "4",
+	"bridge_flow": "1",
+	"initial_layer_speed": "45",
+	"initial_layer_infill_speed": "45",
+	"outer_wall_speed": "45",
+	"inner_wall_speed": "80",
+	"sparse_infill_speed": "150",
+	"internal_solid_infill_speed": "150",
+	"top_surface_speed": "50",
+	"gap_infill_speed": "30",
+	"travel_speed": "200"
+}
@@ -26,6 +26,7 @@ struct SlopeDetection
    bool actived;
 	float normal_z;
    mat3 volume_world_normal_matrix;
+    vec3 up_direction;
 };

 uniform vec4 uniform_color;
@@ -23,6 +23,7 @@ struct SlopeDetection
    bool actived;
 	float normal_z;
    mat3 volume_world_normal_matrix;
+    vec3 up_direction;
 };

 uniform mat4 view_model_matrix;
@@ -71,8 +72,8 @@ void main()
    // Point in homogenous coordinates.
    world_pos = volume_world_matrix * vec4(v_position, 1.0);

-    // z component of normal vector in world coordinate used for slope shading
-    world_normal_z = slope.actived ? (normalize(slope.volume_world_normal_matrix * v_normal)).z : 0.0;
+    // dot product of world normal with up direction, used for slope shading
+    world_normal_z = slope.actived ? dot(normalize(slope.volume_world_normal_matrix * v_normal), slope.up_direction) : 0.0;

    gl_Position = projection_matrix * position;
    // Fill in the scalars for fragment shader clipping. Fragments with any of these components lower than zero are discarded.
@@ -37,6 +37,7 @@ struct SlopeDetection
    bool actived;
 	 float normal_z;
    mat3 volume_world_normal_matrix;
+    vec3 up_direction;
 };
 uniform SlopeDetection slope;

@@ -85,7 +86,7 @@ void main()
              color = LightBlue;
              alpha = 1.0;
         }
-         else if( transformed_normal.z < slope.normal_z - EPSILON)
+         else if( dot(transformed_normal, slope.up_direction) < slope.normal_z - EPSILON)
        {
            color = color * 0.5 + LightRed * 0.5;
            alpha = 1.0;
@@ -24,6 +24,7 @@ struct SlopeDetection
    bool actived;
 	float normal_z;
    mat3 volume_world_normal_matrix;
+    vec3 up_direction;
 };
 uniform SlopeDetection slope;
 void main()
@@ -26,6 +26,7 @@ struct SlopeDetection
    bool actived;
 	float normal_z;
    mat3 volume_world_normal_matrix;
+    vec3 up_direction;
 };

 uniform vec4 uniform_color;
@@ -23,6 +23,7 @@ struct SlopeDetection
    bool actived;
 	float normal_z;
    mat3 volume_world_normal_matrix;
+    vec3 up_direction;
 };

 uniform mat4 view_model_matrix;
@@ -71,8 +72,8 @@ void main()
    // Point in homogenous coordinates.
    world_pos = volume_world_matrix * vec4(v_position, 1.0);

-    // z component of normal vector in world coordinate used for slope shading
-    world_normal_z = slope.actived ? (normalize(slope.volume_world_normal_matrix * v_normal)).z : 0.0;
+    // dot product of world normal with up direction, used for slope shading
+    world_normal_z = slope.actived ? dot(normalize(slope.volume_world_normal_matrix * v_normal), slope.up_direction) : 0.0;

    gl_Position = projection_matrix * position;
    // Fill in the scalars for fragment shader clipping. Fragments with any of these components lower than zero are discarded.
@@ -37,6 +37,7 @@ struct SlopeDetection
    bool actived;
 	 float normal_z;
    mat3 volume_world_normal_matrix;
+    vec3 up_direction;
 };
 uniform SlopeDetection slope;

@@ -87,7 +88,7 @@ void main()
              color = LightBlue;
              alpha = 1.0;
         }
-         else if( transformed_normal.z < slope.normal_z - EPSILON)
+         else if( dot(transformed_normal, slope.up_direction) < slope.normal_z - EPSILON)
        {
            color = color * 0.5 + LightRed * 0.5;
            alpha = 1.0;
@@ -24,6 +24,7 @@ struct SlopeDetection
    bool actived;
 	float normal_z;
    mat3 volume_world_normal_matrix;
+    vec3 up_direction;
 };
 uniform SlopeDetection slope;
 void main()
@@ -0,0 +1,76 @@
+#include "BeltGCode.hpp"
+#include "BeltGCodeWriter.hpp"
+#include "BeltTransform.hpp"
+#include "Print.hpp"
+
+namespace Slic3r {
+
+void BeltGCode::init_belt_writer(Print &print, bool is_bbl_printers)
+{
+    if (!print.config().belt_printer.value)
+        return;
+
+    auto belt_writer = std::make_unique<BeltGCodeWriter>();
+    belt_writer->set_is_bbl_machine(is_bbl_printers);
+    // Axis remap and build volume max are set by base GCode after init_belt_writer returns.
+    belt_writer->set_belt_back_transform(print.config());
+    belt_writer->set_machine_frame_transform(print.config());
+    m_writer = std::move(belt_writer);
+}
+
+void BeltGCode::write_belt_header(GCodeOutputStream &file, const Print &print)
+{
+    if (!print.config().belt_printer.value)
+        return;
+
+    const auto &full_cfg = print.full_print_config();
+    // Slicing rotation: the belt tilt (axis + angle) and the single source of truth
+    // for the physical tilt the G-code viewer uses to enable belt view.
+    file.write_format("; belt_slice_rotation = %s\n", full_cfg.opt_serialize("belt_slice_rotation").c_str());
+    file.write_format("; belt_slice_rotation_angle = %.1f\n", print.config().belt_slice_rotation_angle.value);
+    file.write_format("; belt_slice_rotation_global = %d\n", print.config().belt_slice_rotation_global.value ? 1 : 0);
+    // Pre-slice remap configs
+    file.write_format("; preslice_remap_x = %s\n", full_cfg.opt_serialize("preslice_remap_x").c_str());
+    file.write_format("; preslice_remap_y = %s\n", full_cfg.opt_serialize("preslice_remap_y").c_str());
+    file.write_format("; preslice_remap_z = %s\n", full_cfg.opt_serialize("preslice_remap_z").c_str());
+    file.write_format("; preslice_remap_global = %d\n", print.config().preslice_remap_global.value ? 1 : 0);
+    file.write_format("; belt_preslice_global = %d\n", print.config().belt_preslice_global.value ? 1 : 0);
+    // Machine-frame transform: shear (tan) + scale (1/cos) derived from the belt
+    // tilt angle (or belt_frame_tilt_angle when decoupled).
+    file.write_format("; belt_frame_tilt_decouple = %d\n", print.config().belt_frame_tilt_decouple.value ? 1 : 0);
+    file.write_format("; belt_frame_tilt_angle = %.1f\n", print.config().belt_frame_tilt_angle.value);
+}
+
+void BeltGCode::on_set_origin(const PrintObject * /*obj*/, const Point & /*inst_shift*/)
+{
+    // Global pre-slice mode: adjust origin using computed correction.
+    // Transform the origin through the belt pipeline so that
+    // back_transform(T * origin) = origin (correct machine position).
+    //
+    // Flags that trigger this path:
+    //   belt_preslice_global         — full pipeline (rotation * remap) is global
+    //   preslice_remap_global        — only the pre-slice remap is global
+    //   belt_slice_rotation_global   — slicing rotation treated as global (matches
+    //                                  the per-instance Z-offset added in PrintObjectSlice.cpp)
+    // The XY origin adjustment uses the FULL forward transform, because the
+    // back_transform applied during G-code emission is always the inverse of
+    // the full pipeline.
+    bool use_global = m_config.belt_preslice_global.value
+        || (m_config.preslice_remap_global.value
+            && BeltTransformPipeline::has_preslice_remap(m_config))
+        || (m_config.belt_slice_rotation_global.value
+            && m_config.belt_slice_rotation.value != BeltRotationAxis::None
+            && std::abs(m_config.belt_slice_rotation_angle.value) > EPSILON);
+    if (!use_global || !m_config.belt_printer.value)
+        return;
+
+    // Adjust origin: transform through belt forward pipeline so that
+    // the back-transform correctly recovers model-space positions.
+    Transform3d T = BeltTransformPipeline::build_forward_transform(m_config);
+    Vec2d cur_origin = this->origin();
+    Vec3d origin3d(cur_origin.x(), cur_origin.y(), 0.);
+    Vec3d adjusted = T.linear() * origin3d;
+    this->set_origin(Vec2d(adjusted.x(), adjusted.y()));
+}
+
+} // namespace Slic3r
@@ -0,0 +1,23 @@
+#pragma once
+
+#include "GCode.hpp"
+
+namespace Slic3r {
+
+// Belt-printer-specific GCode export.
+//
+// Inherits from GCode and overrides virtual hooks to:
+// - Create a BeltGCodeWriter instead of a plain GCodeWriter
+// - Write belt configuration to the G-code header
+// - Adjust the origin for global pre-slice transforms when switching instances
+// - Disable arc fitting (G2/G3 not supported on belt printers)
+class BeltGCode : public GCode
+{
+protected:
+    void init_belt_writer(Print &print, bool is_bbl_printers) override;
+    void write_belt_header(GCodeOutputStream &file, const Print &print) override;
+    void on_set_origin(const PrintObject *obj, const Point &inst_shift) override;
+    bool should_disable_arc_fitting() const override { return true; }
+};
+
+} // namespace Slic3r
@@ -0,0 +1,264 @@
+#include "BeltGCodeWriter.hpp"
+#include "FirstLayerPlane.hpp"
+#include "Geometry.hpp"
+#include <boost/log/trivial.hpp>
+
+namespace Slic3r {
+
+namespace {
+
+// Decide whether a particular destination point gets first-layer treatment.
+// When the plane evaluator is active, distance from the plane wins; otherwise
+// fall back to the layer-coarse m_is_first_layer flag set by the caller.
+inline bool belt_point_on_first_layer(
+    const FirstLayerPlane *plane,
+    double                 first_layer_thickness_mm,
+    bool                   layer_first_flag,
+    const Vec3d           &point_slicing_mm)
+{
+    if (plane && plane->is_active())
+        return plane->is_first_layer(point_slicing_mm, first_layer_thickness_mm);
+    return layer_first_flag;
+}
+
+} // namespace
+
+// ---- Belt configuration ---------------------------------------------------
+
+void BeltGCodeWriter::set_belt_back_transform(const PrintConfig &config)
+{
+    m_belt_back_transform.init_from_config(config);
+}
+
+void BeltGCodeWriter::set_machine_frame_transform(const PrintConfig &config)
+{
+    m_machine_frame_transform.init_from_config(config);
+}
+
+Vec3d BeltGCodeWriter::to_machine_coords(const Vec3d &pos) const
+{
+    // Step 1+2: To Cartesian (back_transform + axis_remap).
+    // In world-coordinates mode (PA line / PA pattern calibration) the input
+    // already describes a point relative to the belt surface, so the
+    // slicer->world back-transform is skipped and only the machine kinematics
+    // (axis remap + frame shear/scale) are applied.
+    Vec3d after_back = m_world_coordinates ? pos : m_belt_back_transform.apply(pos);
+    Vec3d result     = apply_axis_remap(after_back);
+    Vec3d after_remap = result;
+    // Step 3: Machine-frame transform (belt frame tilt) applied LAST so it acts
+    // as a global linear transform on the placed coords.
+    Vec3d final = m_machine_frame_transform.apply(result);
+
+    // [BELT-DEBUG] One-shot log per layer transition (i.e. when the input Z
+    // crosses an integer mm boundary) to keep the log volume manageable while
+    // still capturing one sample per ~5 layers.  Shows the full pipeline so
+    // Case A vs Case B can be compared step-by-step.
+    static thread_local int s_last_logged_z = std::numeric_limits<int>::min();
+    int z_bucket = static_cast<int>(std::floor(pos.z() * 5.0));  // every 0.2mm
+    if (z_bucket != s_last_logged_z) {
+        s_last_logged_z = z_bucket;
+        BOOST_LOG_TRIVIAL(trace) << "[BELT-DEBUG] to_machine_coords"
+            << " slicer_in=(" << pos.x() << "," << pos.y() << "," << pos.z() << ")"
+            << " after_back=(" << after_back.x() << "," << after_back.y() << "," << after_back.z() << ")"
+            << " after_remap=(" << after_remap.x() << "," << after_remap.y() << "," << after_remap.z() << ")"
+            << " final=(" << final.x() << "," << final.y() << "," << final.z() << ")"
+            << " mft_active=" << m_machine_frame_transform.is_active()
+            << " back_active=" << m_belt_back_transform.is_active();
+    }
+    return final;
+}
+
+// ---- Overridden movement methods ------------------------------------------
+
+std::string BeltGCodeWriter::travel_to_xy(const Vec2d &point, const std::string &comment)
+{
+    m_pos(0) = point(0);
+    m_pos(1) = point(1);
+
+    this->set_current_position_clear(true);
+    Vec2d point_on_plate = { point(0) - m_x_offset, point(1) - m_y_offset };
+
+    // Belt printer: transform to machine coordinates (XY travel also needs Z due to YZ rotation)
+    Vec3d machine = to_machine_coords(Vec3d(point_on_plate.x(), point_on_plate.y(), m_pos.z()));
+
+    GCodeG1Formatter w;
+    w.emit_xyz(machine);
+    const bool first_layer_for_point = belt_point_on_first_layer(
+        m_first_layer_plane, m_first_layer_thickness_mm, m_is_first_layer,
+        Vec3d(point.x(), point.y(), m_pos.z()));
+    auto speed = first_layer_for_point
+        ? this->config.get_abs_value("initial_layer_travel_speed") : this->config.travel_speed.value;
+    w.emit_f(speed * 60.0);
+    w.emit_comment(GCodeWriter::full_gcode_comment, comment);
+    return w.string();
+}
+
+std::string BeltGCodeWriter::lazy_lift(LiftType lift_type, bool spiral_vase)
+{
+    // Belt printer: force NormalLift since SpiralLift and SlopeLift compute
+    // slope angles that don't account for the YZ coordinate rotation.
+    return GCodeWriter::lazy_lift(LiftType::NormalLift, spiral_vase);
+}
+
+std::string BeltGCodeWriter::eager_lift(const LiftType type)
+{
+    // Belt printer: force NormalLift (SpiralLift/SlopeLift don't account for YZ rotation).
+    return GCodeWriter::eager_lift(LiftType::NormalLift);
+}
+
+std::string BeltGCodeWriter::_travel_to_z(double z, const std::string &comment)
+{
+    m_pos(2) = z;
+
+    double speed = this->config.travel_speed_z.value;
+    if (speed == 0.) {
+        const bool first_layer_for_point = belt_point_on_first_layer(
+            m_first_layer_plane, m_first_layer_thickness_mm, m_is_first_layer,
+            Vec3d(m_pos.x(), m_pos.y(), z));
+        speed = first_layer_for_point ? this->config.get_abs_value("initial_layer_travel_speed")
+                                      : this->config.travel_speed.value;
+    }
+
+    // Belt printer: a Z-only move in slicing frame needs to emit both Y and Z in machine coords.
+    Vec3d machine = to_machine_coords(Vec3d(m_pos.x() - m_x_offset, m_pos.y() - m_y_offset, z));
+
+    GCodeG1Formatter w;
+    w.emit_xyz(machine);
+    w.emit_f(speed * 60.0);
+    w.emit_comment(GCodeWriter::full_gcode_comment, comment);
+    return w.string();
+}
+
+std::string BeltGCodeWriter::extrude_to_xy(const Vec2d &point, double dE, const std::string &comment, bool force_no_extrusion)
+{
+    m_pos(0) = point(0);
+    m_pos(1) = point(1);
+    if (std::abs(dE) <= std::numeric_limits<double>::epsilon())
+        force_no_extrusion = true;
+
+    if (!force_no_extrusion)
+        filament()->extrude(dE);
+
+    Vec2d point_on_plate = { point(0) - m_x_offset, point(1) - m_y_offset };
+
+    // Belt printer: transform and emit XYZ (Y and Z are coupled)
+    Vec3d machine = to_machine_coords(Vec3d(point_on_plate.x(), point_on_plate.y(), m_pos.z()));
+
+    GCodeG1Formatter w;
+    w.emit_xyz(machine);
+    if (!force_no_extrusion)
+        w.emit_e(filament()->E());
+    w.emit_comment(GCodeWriter::full_gcode_comment, comment);
+    return w.string();
+}
+
+std::string BeltGCodeWriter::extrude_to_xyz(const Vec3d &point, double dE, const std::string &comment, bool force_no_extrusion)
+{
+    m_pos = point;
+    m_lifted = 0;
+    if (!force_no_extrusion)
+        filament()->extrude(dE);
+
+    Vec3d point_on_plate = { point(0) - m_x_offset, point(1) - m_y_offset, point(2) };
+    point_on_plate = to_machine_coords(point_on_plate);
+
+    GCodeG1Formatter w;
+    w.emit_xyz(point_on_plate);
+    if (!force_no_extrusion)
+        w.emit_e(filament()->E());
+    w.emit_comment(GCodeWriter::full_gcode_comment, comment);
+    return w.string();
+}
+
+std::string BeltGCodeWriter::travel_to_xyz(const Vec3d &point, const std::string &comment, bool force_z)
+{
+    // Belt-specific override of travel_to_xyz.
+    // Key differences from base:
+    // 1. All coordinates go through to_machine_coords()
+    // 2. Always emit full XYZ (can't split XY and Z due to coupling)
+    // 3. Lift type forced to NormalLift (handled by lazy_lift/eager_lift overrides)
+
+    Vec3d dest_point = point;
+    const bool first_layer_for_point = belt_point_on_first_layer(
+        m_first_layer_plane, m_first_layer_thickness_mm, m_is_first_layer, point);
+    auto travel_speed =
+        first_layer_for_point ? this->config.get_abs_value("initial_layer_travel_speed")
+                              : this->config.travel_speed.value;
+
+    // Handle pending z_hop
+    if (std::abs(m_to_lift) > EPSILON) {
+        assert(std::abs(m_lifted) < EPSILON);
+        if ((!this->is_current_position_clear() || m_pos != dest_point) &&
+            m_to_lift + m_pos(2) > point(2)) {
+            m_lifted = m_to_lift + m_pos(2) - point(2);
+            dest_point(2) = m_to_lift + m_pos(2);
+        }
+        m_to_lift = 0.;
+
+        std::string slop_move;
+        Vec3d source = { m_pos(0) - m_x_offset, m_pos(1) - m_y_offset, m_pos(2) };
+        Vec3d target = { dest_point(0) - m_x_offset, dest_point(1) - m_y_offset, dest_point(2) };
+        Vec3d delta = target - source;
+        Vec2d delta_no_z = { delta(0), delta(1) };
+
+        if (delta(2) > 0 && delta_no_z.norm() != 0.0f) {
+            // Belt: SpiralLift and SlopeLift are disabled (lazy_lift forces NormalLift),
+            // but handle NormalLift and fallthrough.
+            if (m_to_lift_type == LiftType::SlopeLift &&
+                this->is_current_position_clear() &&
+                atan2(delta(2), delta_no_z.norm()) < this->filament()->travel_slope()) {
+                Vec2d temp = delta_no_z.normalized() * delta(2) / tan(this->filament()->travel_slope());
+                Vec3d slope_top_point = Vec3d(temp(0), temp(1), delta(2)) + source;
+                slope_top_point = to_machine_coords(slope_top_point);
+                GCodeG1Formatter w0;
+                w0.emit_xyz(slope_top_point);
+                w0.emit_f(travel_speed * 60.0);
+                w0.emit_comment(GCodeWriter::full_gcode_comment, comment);
+                slop_move = w0.string();
+            }
+            else if (m_to_lift_type == LiftType::NormalLift) {
+                slop_move = _travel_to_z(target.z(), "normal lift Z");
+            }
+        }
+
+        std::string xy_z_move;
+        {
+            Vec3d emit_target = to_machine_coords(target);
+            GCodeG1Formatter w0;
+            // Belt mode: always emit full XYZ since Y and Z are coupled
+            w0.emit_xyz(emit_target);
+            w0.emit_f(travel_speed * 60.0);
+            w0.emit_comment(GCodeWriter::full_gcode_comment, comment);
+            xy_z_move = w0.string();
+        }
+        m_pos = dest_point;
+        this->set_current_position_clear(true);
+        return slop_move + xy_z_move;
+    }
+    else if (!force_z && !this->will_move_z(point(2))) {
+        double nominal_z = m_pos(2) - m_lifted;
+        m_lifted -= (point(2) - nominal_z);
+        if (std::abs(m_lifted) < EPSILON)
+            m_lifted = 0.;
+        this->set_current_position_clear(true);
+        return this->travel_to_xy(to_2d(point));
+    }
+    else {
+        m_lifted = 0;
+    }
+
+    Vec3d point_on_plate = { dest_point(0) - m_x_offset, dest_point(1) - m_y_offset, dest_point(2) };
+    point_on_plate = to_machine_coords(point_on_plate);
+
+    // Belt mode: always emit full XYZ
+    GCodeG1Formatter w;
+    w.emit_xyz(point_on_plate);
+    w.emit_f(this->config.travel_speed.value * 60.0);
+    w.emit_comment(GCodeWriter::full_gcode_comment, comment);
+
+    m_pos = dest_point;
+    this->set_current_position_clear(true);
+    return w.string();
+}
+
+} // namespace Slic3r
@@ -0,0 +1,64 @@
+#pragma once
+
+#include "GCodeWriter.hpp"
+#include "GCode/BeltBackTransform.hpp"
+#include "GCode/MachineFrameTransform.hpp"
+
+namespace Slic3r {
+
+class FirstLayerPlane;
+
+// Belt-printer-specific GCode writer.
+//
+// Inherits from GCodeWriter and overrides movement methods to apply
+// coordinate transformation (back-transform, axis remap, machine-frame
+// transform) and emit coupled XYZ moves (Y and Z are coupled due to belt tilt).
+class BeltGCodeWriter : public GCodeWriter
+{
+public:
+    BeltGCodeWriter() : GCodeWriter() {}
+
+    // Belt configuration (axis remap is inherited from GCodeWriter)
+    void set_belt_back_transform(const PrintConfig &config);
+    void set_machine_frame_transform(const PrintConfig &config);
+    Vec3d to_machine_coords(const Vec3d &pos) const;
+
+    // World-coordinates mode: incoming coordinates are treated as points
+    // relative to the physical belt surface (X across, Y along the belt,
+    // Z height above it) instead of slicing-frame coordinates — the
+    // slicer->world back-transform is skipped. Used by the PA line / PA
+    // pattern calibration generators, whose logical bed coordinates describe
+    // first-layer drawings on the build surface.
+    void set_world_coordinates(bool enable) { m_world_coordinates = enable; }
+
+    // First-layer plane: when set to a non-null active evaluator, travel
+    // speed selection consults the plane per-move and uses
+    // initial_layer_travel_speed for points within first_layer_height_mm
+    // of the plane (regardless of slicing layer index).
+    void set_first_layer_plane(const FirstLayerPlane *plane,
+                               double first_layer_height_mm) {
+        m_first_layer_plane         = plane;
+        m_first_layer_thickness_mm  = first_layer_height_mm;
+    }
+
+    // Overridden movement methods
+    std::string travel_to_xy(const Vec2d &point, const std::string &comment = std::string()) override;
+    std::string travel_to_xyz(const Vec3d &point, const std::string &comment = std::string(), bool force_z = false) override;
+    std::string extrude_to_xy(const Vec2d &point, double dE, const std::string &comment = std::string(), bool force_no_extrusion = false) override;
+    std::string extrude_to_xyz(const Vec3d &point, double dE, const std::string &comment = std::string(), bool force_no_extrusion = false) override;
+    std::string lazy_lift(LiftType lift_type = LiftType::NormalLift, bool spiral_vase = false) override;
+    std::string eager_lift(const LiftType type) override;
+
+protected:
+    std::string _travel_to_z(double z, const std::string &comment) override;
+
+private:
+    BeltBackTransform     m_belt_back_transform;
+    MachineFrameTransform m_machine_frame_transform;
+    bool                  m_world_coordinates = false;
+    // Borrowed pointer; lifetime owned by GCode.  null = inactive.
+    const FirstLayerPlane *m_first_layer_plane = nullptr;
+    double          m_first_layer_thickness_mm = 0.;
+};
+
+} // namespace Slic3r
@@ -0,0 +1,143 @@
+#include "BeltSliceStrategy.hpp"
+#include "Model.hpp"
+
+#include <limits>
+
+#include <boost/log/trivial.hpp>
+#ifdef SLIC3R_BELT_DIAGNOSTIC_LOG
+#include <iomanip>
+#include <sstream>
+#include <thread>
+#endif
+
+namespace Slic3r {
+
+void BeltSliceStrategy::apply_preslice_transforms(Transform3d           &trafo,
+                                                  const PrintConfig     &config,
+                                                  const ModelVolumePtrs &model_volumes,
+                                                  double                *out_belt_min_z)
+{
+    // 1. Standalone pre-slice axis remap (works without belt mode).
+    const bool has_remap = BeltTransformPipeline::has_preslice_remap(config);
+    if (has_remap)
+        trafo = BeltTransformPipeline::build_preslice_remap(config) * trafo;
+
+    // 2. Belt rotation — the sole mesh-side belt transform (matching
+    //    BeltTransformPipeline::build_forward_transform).  Only active in
+    //    belt-printer mode.
+    bool has_rotation = false;
+    if (config.belt_printer.value) {
+        const Matrix3d rot = BeltTransformPipeline::build_rotation_matrix(config, &has_rotation);
+        if (has_rotation) {
+            Transform3d belt_xform = Transform3d::Identity();
+            belt_xform.linear() = rot;
+            trafo = belt_xform * trafo;
+        }
+    }
+
+    if (!has_remap && !has_rotation)
+        return;
+
+    // 3. Z-shift — detect if the mesh clips below the build plate after the
+    // transforms and lift it.  Each mesh vertex must be brought into object space
+    // via mv->get_matrix() before applying the full trafo (which is in object
+    // space).  Missing this on assemblies (where per-volume get_matrix() positions
+    // each volume within the object) would compute min_z against mesh-local vertex
+    // coordinates rather than object-space coordinates, so volumes translated along
+    // the slicer's Z axis would be silently excluded from the bound check.
+#ifdef SLIC3R_BELT_DIAGNOSTIC_LOG
+    // Capture the incoming trafo for diagnostic logging.
+    // This is the slicer-frame transform AFTER remap + rotation but BEFORE z_shift.
+    const Transform3d trafo_pre_shift = trafo;
+    auto log_mat = [](const Matrix3d &m) {
+        std::ostringstream ss;
+        ss << std::fixed << std::setprecision(4);
+        ss << "[[" << m(0,0) << "," << m(0,1) << "," << m(0,2) << "],"
+           << "["  << m(1,0) << "," << m(1,1) << "," << m(1,2) << "],"
+           << "["  << m(2,0) << "," << m(2,1) << "," << m(2,2) << "]]";
+        return ss.str();
+    };
+    auto log_vec3 = [](const Vec3d &v) {
+        std::ostringstream ss;
+        ss << std::fixed << std::setprecision(4);
+        ss << "(" << v.x() << "," << v.y() << "," << v.z() << ")";
+        return ss.str();
+    };
+    BOOST_LOG_TRIVIAL(trace) << "[BELT-DEBUG] apply_preslice_transforms enter"
+        << " has_rotation=" << has_rotation
+        << " has_remap=" << has_remap
+        << " trafo.linear=" << log_mat(trafo_pre_shift.linear())
+        << " trafo.translation=" << log_vec3(trafo_pre_shift.translation())
+        << " volumes=" << model_volumes.size();
+#endif
+
+    double min_z = std::numeric_limits<double>::max();
+#ifdef SLIC3R_BELT_DIAGNOSTIC_LOG
+    int vol_idx = 0;
+#endif
+    for (const ModelVolume *mv : model_volumes) {
+#ifdef SLIC3R_BELT_DIAGNOSTIC_LOG
+        if (!mv->is_model_part()) { ++vol_idx; continue; }
+#else
+        if (!mv->is_model_part()) continue;
+#endif
+        Transform3d vol_trafo = trafo * mv->get_matrix();
+        const auto &its = mv->mesh().its;
+#ifdef SLIC3R_BELT_DIAGNOSTIC_LOG
+        // Per-volume bbox in mesh-frame and post-trafo slicer-frame.
+        Vec3d mesh_min(std::numeric_limits<double>::max(), std::numeric_limits<double>::max(), std::numeric_limits<double>::max());
+        Vec3d mesh_max(std::numeric_limits<double>::lowest(), std::numeric_limits<double>::lowest(), std::numeric_limits<double>::lowest());
+        Vec3d slicer_min(std::numeric_limits<double>::max(), std::numeric_limits<double>::max(), std::numeric_limits<double>::max());
+        Vec3d slicer_max(std::numeric_limits<double>::lowest(), std::numeric_limits<double>::lowest(), std::numeric_limits<double>::lowest());
+        double vol_min_z = std::numeric_limits<double>::max();
+#endif
+        for (const stl_vertex &v : its.vertices) {
+            Vec3d vm = v.cast<double>();
+            Vec3d pt = vol_trafo * vm;
+            min_z = std::min(min_z, pt.z());
+#ifdef SLIC3R_BELT_DIAGNOSTIC_LOG
+            mesh_min = mesh_min.cwiseMin(vm);
+            mesh_max = mesh_max.cwiseMax(vm);
+            slicer_min = slicer_min.cwiseMin(pt);
+            slicer_max = slicer_max.cwiseMax(pt);
+            vol_min_z = std::min(vol_min_z, pt.z());
+#endif
+        }
+#ifdef SLIC3R_BELT_DIAGNOSTIC_LOG
+        BOOST_LOG_TRIVIAL(trace) << "[BELT-DEBUG]   vol[" << vol_idx
+            << "] id=" << mv->id().id << " name='" << mv->name << "'"
+            << " mesh_bbox_min=" << log_vec3(mesh_min) << " mesh_bbox_max=" << log_vec3(mesh_max)
+            << " get_matrix.translation=" << log_vec3(mv->get_matrix().translation())
+            << " slicer_bbox_min=" << log_vec3(slicer_min) << " slicer_bbox_max=" << log_vec3(slicer_max)
+            << " vol_min_z=" << vol_min_z;
+        ++vol_idx;
+#endif
+    }
+    const double z_shift_val = (min_z < 0. && min_z != std::numeric_limits<double>::max()) ? -min_z : 0.;
+#ifdef SLIC3R_BELT_DIAGNOSTIC_LOG
+    BOOST_LOG_TRIVIAL(trace) << "[BELT-DEBUG] combined min_z=" << min_z
+        << " z_shift_val=" << z_shift_val;
+#endif
+    if (z_shift_val > 0.) {
+        Transform3d z_shift = Transform3d::Identity();
+        z_shift.matrix()(2, 3) = z_shift_val;
+        trafo = z_shift * trafo;
+    }
+    // out_belt_min_z is only meaningful in belt mode; the standalone-remap path
+    // never reported it.
+    if (out_belt_min_z && config.belt_printer.value) {
+        const double new_val = (min_z != std::numeric_limits<double>::max()) ? min_z : 0.;
+#ifdef SLIC3R_BELT_DIAGNOSTIC_LOG
+        BOOST_LOG_TRIVIAL(trace) << "[BELT-DEBUG] write m_belt_min_z tid=" << std::this_thread::get_id()
+            << " target=" << out_belt_min_z << " old=" << *out_belt_min_z << " new=" << new_val;
+#endif
+        *out_belt_min_z = new_val;
+    }
+#ifdef SLIC3R_BELT_DIAGNOSTIC_LOG
+    BOOST_LOG_TRIVIAL(trace) << "[BELT-DEBUG] apply_preslice_transforms exit"
+        << " final_trafo.linear=" << log_mat(trafo.linear())
+        << " final_trafo.translation=" << log_vec3(trafo.translation());
+#endif
+}
+
+} // namespace Slic3r
@@ -0,0 +1,36 @@
+#pragma once
+
+#include "libslic3r.h"
+#include "Point.hpp"
+#include "BeltTransform.hpp"
+#include "PrintConfig.hpp"
+#include "Model.hpp"
+
+namespace Slic3r {
+
+// Belt printer / pre-slice transform strategy.
+//
+// Composes, in order, the pre-slice mesh transforms applied before slicing:
+//   1. Pre-slice axis remap (standalone — works without belt mode)
+//   2. Belt rotation (the sole mesh-side belt transform; shear & scale are a
+//      g-code-side stage, see MachineFrameTransform)
+//   3. Per-object Z-shift that lifts the mesh above the build plate
+//
+// Isolates this belt/remap-specific logic from the generic slicing pipeline in
+// PrintObjectSlice.cpp.
+class BeltSliceStrategy
+{
+public:
+    // Apply the pre-slice remap + belt rotation + Z-shift to `trafo` in place.
+    // No-op when neither a remap nor a belt rotation is configured.
+    //
+    // out_belt_min_z (if non-null) receives the minimum mesh Z after the
+    // transforms, but only in belt-printer mode — the standalone-remap path
+    // never reported it.
+    static void apply_preslice_transforms(Transform3d           &trafo,
+                                          const PrintConfig     &config,
+                                          const ModelVolumePtrs &model_volumes,
+                                          double                *out_belt_min_z = nullptr);
+};
+
+} // namespace Slic3r
@@ -0,0 +1,223 @@
+#include "BeltTransform.hpp"
+#include "Model.hpp"
+
+#include <limits>
+
+namespace Slic3r {
+
+// ---- Matrix builders ------------------------------------------------------
+
+Transform3d BeltTransformPipeline::build_preslice_remap(const PrintConfig &config)
+{
+    Transform3d pre_remap = Transform3d::Identity();
+    if (!has_preslice_remap(config))
+        return pre_remap;
+
+    int pre_rx = int(config.preslice_remap_x.value);
+    int pre_ry = int(config.preslice_remap_y.value);
+    int pre_rz = int(config.preslice_remap_z.value);
+
+    // Each remap value selects a source axis and sign.
+    auto remap_column = [](int r) -> Vec3d {
+        int axis = r % 3;
+        Vec3d col = Vec3d::Zero();
+        if (r < 3)      col[axis] =  1.0;  // +axis
+        else if (r < 6) col[axis] = -1.0;  // -axis
+        else            col[axis] = -1.0;  // Rev: max - pos = -(pos - max)
+        return col;
+    };
+
+    Matrix3d remap_lin;
+    remap_lin.col(0) = remap_column(pre_rx);
+    remap_lin.col(1) = remap_column(pre_ry);
+    remap_lin.col(2) = remap_column(pre_rz);
+    pre_remap.linear() = remap_lin;
+
+    // Translation for Rev modes (needs build volume extents).
+    if (pre_rx >= 6 || pre_ry >= 6 || pre_rz >= 6) {
+        BoundingBoxf bbox_bed(config.printable_area.values);
+        Vec3d vol_max(bbox_bed.max.x(), bbox_bed.max.y(),
+                      config.printable_height.value);
+        Vec3d remap_trans = Vec3d::Zero();
+        auto add_rev = [&](int r, int out) {
+            if (r >= 6) remap_trans[out] = vol_max[r % 3];
+        };
+        add_rev(pre_rx, 0);
+        add_rev(pre_ry, 1);
+        add_rev(pre_rz, 2);
+        pre_remap.translation() = remap_trans;
+    }
+
+    return pre_remap;
+}
+
+Matrix3d BeltTransformPipeline::build_rotation_matrix(const PrintConfig &config, bool *has_rot_out)
+{
+    BeltRotationAxis axis = config.belt_slice_rotation.value;
+    double angle_deg = config.belt_slice_rotation_angle.value;
+    bool active = axis != BeltRotationAxis::None && std::abs(angle_deg) > EPSILON;
+    if (has_rot_out) *has_rot_out = active;
+    if (!active)
+        return Matrix3d::Identity();
+    double angle_rad = Geometry::deg2rad(angle_deg);
+    Vec3d unit_axis;
+    switch (axis) {
+    case BeltRotationAxis::X: unit_axis = Vec3d::UnitX(); break;
+    case BeltRotationAxis::Y: unit_axis = Vec3d::UnitY(); break;
+    case BeltRotationAxis::Z: unit_axis = Vec3d::UnitZ(); break;
+    default:                  return Matrix3d::Identity();
+    }
+    return Eigen::AngleAxisd(angle_rad, unit_axis).toRotationMatrix();
+}
+
+Transform3d BeltTransformPipeline::build_forward_transform(const PrintConfig &config)
+{
+    // Mesh-side belt transform: rotation applied after the pre-slice axis remap.
+    // (Shear & scale are a g-code-side stage, not part of the mesh transform.)
+    Transform3d pre_remap = build_preslice_remap(config);
+    Matrix3d    rot       = build_rotation_matrix(config);
+
+    Transform3d combined = Transform3d::Identity();
+    combined.linear() = rot;
+    combined = combined * pre_remap;
+    return combined;
+}
+
+// ---- Bounding box remap ---------------------------------------------------
+
+BoundingBoxf3 BeltTransformPipeline::remap_bbox(const BoundingBoxf3 &bb, const PrintConfig &config)
+{
+    int pre_rx = int(config.preslice_remap_x.value);
+    int pre_ry = int(config.preslice_remap_y.value);
+    int pre_rz = int(config.preslice_remap_z.value);
+
+    if (pre_rx == int(RemapAxis::PosX) &&
+        pre_ry == int(RemapAxis::PosY) &&
+        pre_rz == int(RemapAxis::PosZ))
+        return bb;  // Identity remap.
+
+    auto remap_coord = [](int r, const Vec3d &v) -> double {
+        int axis = r % 3;
+        if (r < 3) return v[axis];
+        return -v[axis];
+    };
+
+    Vec3d mn = bb.min.cast<double>(), mx = bb.max.cast<double>();
+    BoundingBoxf3 rbb;
+    for (int i = 0; i < 8; ++i) {
+        Vec3d c((i & 1) ? mx.x() : mn.x(),
+                (i & 2) ? mx.y() : mn.y(),
+                (i & 4) ? mx.z() : mn.z());
+        Vec3d rc(remap_coord(pre_rx, c), remap_coord(pre_ry, c), remap_coord(pre_rz, c));
+        if (i == 0) rbb = BoundingBoxf3(rc, rc);
+        else rbb.merge(rc);
+    }
+    return rbb;
+}
+
+BoundingBoxf3 BeltTransformPipeline::remap_bbox(const ModelObject &model_object, const PrintConfig &config)
+{
+    return remap_bbox(model_object.raw_bounding_box(), config);
+}
+
+// ---- Belt floor parameters ------------------------------------------------
+
+// Shared implementation for both PrintConfig and DynamicPrintConfig.
+// Template avoids duplicating the math for the two config types.
+namespace {
+
+template<typename Config>
+BeltTransformPipeline::BeltHeightResult compute_belt_height_and_floor_impl(
+    const Config &config, const BoundingBoxf3 &bb, double original_height)
+{
+    BeltTransformPipeline::BeltHeightResult result;
+    result.object_height = original_height;
+
+    // Extract the mesh rotation from config (the sole mesh-side belt transform).
+    BeltRotationAxis rot_axis;
+    double           rot_angle;
+
+    if constexpr (std::is_same_v<Config, PrintConfig>) {
+        rot_axis  = config.belt_slice_rotation.value;
+        rot_angle = config.belt_slice_rotation_angle.value;
+    } else {
+        // DynamicPrintConfig path
+        auto get_float = [&](const char *key) {
+            auto *opt = config.template option<ConfigOptionFloat>(key);
+            return opt ? opt->value : 0.0;
+        };
+        auto get_rot_axis = [&](const char *key) {
+            auto *opt = config.template option<ConfigOptionEnum<BeltRotationAxis>>(key);
+            return opt ? opt->value : BeltRotationAxis::None;
+        };
+        rot_axis  = get_rot_axis("belt_slice_rotation");
+        rot_angle = get_float("belt_slice_rotation_angle");
+    }
+
+    bool has_rotation = rot_axis != BeltRotationAxis::None && std::abs(rot_angle) > EPSILON;
+    if (!has_rotation)
+        return result;
+
+    // Rotation path: sweep the 8 bbox corners through R to get the rotated height,
+    // then derive the belt floor (the image of machine-Z = 0 under R).
+    double angle_rad = Geometry::deg2rad(rot_angle);
+    Vec3d unit_axis;
+    switch (rot_axis) {
+    case BeltRotationAxis::X: unit_axis = Vec3d::UnitX(); break;
+    case BeltRotationAxis::Y: unit_axis = Vec3d::UnitY(); break;
+    case BeltRotationAxis::Z: unit_axis = Vec3d::UnitZ(); break;
+    default:                  unit_axis = Vec3d::UnitX(); break;
+    }
+    Matrix3d R = Eigen::AngleAxisd(angle_rad, unit_axis).toRotationMatrix();
+    double min_rz = std::numeric_limits<double>::max();
+    double max_rz = std::numeric_limits<double>::lowest();
+    for (int i = 0; i < 8; ++i) {
+        Vec3d c((i & 1) ? bb.max.x() : bb.min.x(),
+                (i & 2) ? bb.max.y() : bb.min.y(),
+                (i & 4) ? bb.max.z() : bb.min.z());
+        double z = (R * c).z();
+        min_rz = std::min(min_rz, z);
+        max_rz = std::max(max_rz, z);
+    }
+    result.object_height = max_rz - min_rz;
+
+    // Belt floor in slicer-frame is the image of z_machine = 0 under R.
+    //   R(+α, X): point (·, y, 0) → (·, cos α · y, sin α · y) ⇒ z = tan(α) · y_s
+    //   R(+α, Y): point (x, ·, 0) → (cos α · x, ·, -sin α · x) ⇒ z = -tan(α) · x_s
+    //   R(+α, Z): point (·, ·, 0) → (·, ·, 0); no tilt → no floor
+    double sin_a = std::sin(angle_rad), cos_a = std::cos(angle_rad);
+    switch (rot_axis) {
+    case BeltRotationAxis::X:
+        result.floor_params.shear_factor = (std::abs(cos_a) > EPSILON) ?  sin_a / cos_a : 0.;
+        result.floor_params.from_axis    = 1; // Y
+        break;
+    case BeltRotationAxis::Y:
+        result.floor_params.shear_factor = (std::abs(cos_a) > EPSILON) ? -sin_a / cos_a : 0.;
+        result.floor_params.from_axis    = 0; // X
+        break;
+    case BeltRotationAxis::Z:
+    default:
+        result.floor_params.shear_factor = 0.0;
+        result.floor_params.from_axis    = 1;
+        break;
+    }
+    result.floor_params.z_shift = bb.min.z() + ((min_rz < 0.) ? -min_rz : 0.);
+
+    return result;
+}
+
+} // anonymous namespace
+
+BeltTransformPipeline::BeltHeightResult BeltTransformPipeline::compute_belt_height_and_floor(
+    const PrintConfig &config, const BoundingBoxf3 &remapped_bbox, double original_height)
+{
+    return compute_belt_height_and_floor_impl(config, remapped_bbox, original_height);
+}
+
+BeltTransformPipeline::BeltHeightResult BeltTransformPipeline::compute_belt_height_and_floor(
+    const DynamicPrintConfig &config, const BoundingBoxf3 &remapped_bbox, double original_height)
+{
+    return compute_belt_height_and_floor_impl(config, remapped_bbox, original_height);
+}
+
+} // namespace Slic3r
@@ -0,0 +1,152 @@
+#pragma once
+
+#include "libslic3r.h"
+#include "Point.hpp"
+#include "BoundingBox.hpp"
+#include "PrintConfig.hpp"
+#include "Geometry.hpp"
+
+#include <cmath>
+
+namespace Slic3r {
+
+class ModelObject;
+
+// Shared belt-printer transform math.
+//
+// The pre-slice pipeline applied in PrintObjectSlice.cpp is:
+//     trafo_out = z_shift * rotation * pre_remap * trafo_in
+//
+// Rotation is the sole mesh-side belt transform; shear & scale are applied
+// to the g-code instead (see MachineFrameTransform).  This class provides the
+// building blocks so every call site uses the same implementation.  z_shift is
+// object-dependent (computed from mesh vertex bounds) and is NOT included in
+// build_forward_transform().  The machine-frame shear/scale is derived directly
+// from the tilt angle in MachineFrameTransform and no longer lives here.
+//
+// Design note: this mesh-rotation approach replaced an earlier pre-shear
+// method (now removed).  While that initial pre-shear method was instrumental
+// in getting belt printer slicing off the ground in the first place, its place is
+// in the past.  A big thank you goes to the Unlayered3D team, who recommended 
+// switching to a pre-slice rotation stage instead.  Doing so keeps the slicing 
+// operation isometric — no distortion of the sliced geometry — while the 
+// non-orthogonal machine-axis compensation is confined to a g-code-side shear/scale
+// derived from the same tilt angle.
+// 
+// This fixed a number of issues, including several issues noticed by hotcubcar
+// regarding adaptive infills not working, gyroid becoming anisotropic, and more 
+// that were all mostly resolved as a result of the switch.
+// 
+// This also means that the pre-slice rotation transform methodology can be used 
+// more cleanly on non-belt printers.
+// - HarrierPigeon (Joseph Robertson)
+
+class BeltTransformPipeline
+{
+public:
+    // ---- Identity checks --------------------------------------------------
+
+    static bool has_preslice_remap(const PrintConfig &config)
+    {
+        return int(config.preslice_remap_x.value) != int(RemapAxis::PosX) ||
+               int(config.preslice_remap_y.value) != int(RemapAxis::PosY) ||
+               int(config.preslice_remap_z.value) != int(RemapAxis::PosZ);
+    }
+
+    // Overload accepting DynamicPrintConfig (used in static slicing_parameters).
+    static bool has_preslice_remap(const DynamicPrintConfig &config)
+    {
+        auto get_int = [&](const char *key) -> int {
+            auto *opt = config.option<ConfigOptionEnum<RemapAxis>>(key);
+            return opt ? int(opt->value) : 0;
+        };
+        return get_int("preslice_remap_x") != int(RemapAxis::PosX) ||
+               get_int("preslice_remap_y") != int(RemapAxis::PosY) ||
+               get_int("preslice_remap_z") != int(RemapAxis::PosZ);
+    }
+
+    static bool has_rotation(const PrintConfig &config)
+    {
+        return config.belt_slice_rotation.value != BeltRotationAxis::None &&
+               std::abs(config.belt_slice_rotation_angle.value) > EPSILON;
+    }
+
+    // Physical belt tilt derived from the slicing rotation — the single source of
+    // truth for bed rendering, support gravity tilt and the bed-exclusion
+    // projection.  Returns the tilt magnitude in degrees split onto the X and Y
+    // build-plate tilt axes according to the rotation axis:
+    //   rotation about X  → tilt_x = angle   (gantry tilts in the YZ plane)
+    //   rotation about Y  → tilt_y = angle   (gantry tilts in the XZ plane)
+    //   rotation about Z / None → no tilt    (in-plane spin doesn't tilt the belt)
+    // The magnitude uses abs(angle) so a negative rotation still reports a positive
+    // physical tilt.
+    struct PhysicalTilt { double tilt_x_deg = 0.; double tilt_y_deg = 0.; };
+
+    static PhysicalTilt physical_tilt(BeltRotationAxis axis, double angle_deg)
+    {
+        PhysicalTilt t;
+        double mag = std::abs(angle_deg);
+        switch (axis) {
+        case BeltRotationAxis::X: t.tilt_x_deg = mag; break;
+        case BeltRotationAxis::Y: t.tilt_y_deg = mag; break;
+        default: break; // Z / None: no physical tilt
+        }
+        return t;
+    }
+
+    static PhysicalTilt physical_tilt(const PrintConfig &config)
+    {
+        return physical_tilt(config.belt_slice_rotation.value,
+                             config.belt_slice_rotation_angle.value);
+    }
+
+    // ---- Matrix builders --------------------------------------------------
+
+    // Build the pre-slice axis remap transform (includes Rev-mode translation).
+    static Transform3d build_preslice_remap(const PrintConfig &config);
+
+    // Build the 3x3 rotation matrix from belt_slice_rotation* config.
+    // Returns Identity if rotation axis is None or angle is ~0.
+    // Also sets has_rot_out if non-null.
+    static Matrix3d build_rotation_matrix(const PrintConfig &config, bool *has_rot_out = nullptr);
+
+    // Combined forward transform (rotation * pre_remap) — the mesh-side belt
+    // transform that BeltSliceStrategy applies and BeltBackTransform inverts.
+    // Does NOT include the per-object Z-shift.
+    static Transform3d build_forward_transform(const PrintConfig &config);
+
+    // ---- Bounding box remap -----------------------------------------------
+
+    // Remap a bounding box through the pre-slice axis remap.
+    // Returns the original bbox if remap is identity.
+    static BoundingBoxf3 remap_bbox(const BoundingBoxf3 &bb, const PrintConfig &config);
+    static BoundingBoxf3 remap_bbox(const ModelObject &model_object, const PrintConfig &config);
+
+    // ---- Belt floor parameters --------------------------------------------
+
+    struct BeltFloorParams {
+        double shear_factor = 0.0;
+        int    from_axis    = 1;
+        double z_shift      = 0.0;
+    };
+
+    // Result of computing belt height + floor params.
+    struct BeltHeightResult {
+        double          object_height;  // Effective object height after shear/scale
+        BeltFloorParams floor_params;
+    };
+
+    // Compute effective object height and belt floor parameters from config
+    // and pre-remapped bounding box.  original_height is the input height
+    // (bb.size().z() or model_object.max_z()).
+    static BeltHeightResult compute_belt_height_and_floor(
+        const PrintConfig &config, const BoundingBoxf3 &remapped_bbox,
+        double original_height);
+
+    // Overload for DynamicPrintConfig (used by static slicing_parameters).
+    static BeltHeightResult compute_belt_height_and_floor(
+        const DynamicPrintConfig &config, const BoundingBoxf3 &remapped_bbox,
+        double original_height);
+};
+
+} // namespace Slic3r
@@ -895,6 +895,10 @@ void make_brim(const Print& print, PrintTryCancel try_cancel, Polygons& islands_
    std::map<ObjectID, ExPolygons>* objectBrimAreasOut,
    std::map<ObjectID, ExPolygons>* supportBrimAreasOut)
 {
+    // Belt printer: brim is not compatible with belt printing.
+    if (print.config().belt_printer.value)
+        return;
+
    std::map<ObjectID, double> brim_width_map;
    std::map<ObjectID, ExPolygons> brimAreaMap;
    std::map<ObjectID, ExPolygons> supportBrimAreaMap;
@@ -176,6 +176,31 @@ BuildVolume::BuildVolume(const std::vector<Vec2d> &printable_area, const double
    BOOST_LOG_TRIVIAL(debug) << "BuildVolume printable_area clasified as: " << this->type_name();
 }

+void BuildVolume::set_belt_printer(bool enabled, double angle_deg, bool infinite_y)
+{
+    m_is_belt_printer = enabled;
+    m_belt_angle = angle_deg;
+    m_belt_infinite_y = infinite_y;
+
+    // Restart from the unmodified bbox each call. Without this, toggling
+    // belt mode off (or switching infinite_y true→false) would leave the
+    // extents inflated and break collision / object_state checks.
+    BoundingBoxf bboxf = get_extents(m_bed_shape);
+    m_bboxf = BoundingBoxf3{ to_3d(bboxf.min, 0.), to_3d(bboxf.max, m_max_print_height) };
+
+    if (enabled) {
+        if (infinite_y) {
+            // Extend the Y bound to a very large value for infinite belt.
+            m_bboxf.max.y() = 100000.;
+        }
+        // Belt printer: the Z extent already equals printable_height (set above), which
+        // is the usable vertical clearance above the belt. The gantry's axis range is
+        // sized to reach height/cos(tilt), so no diagonal scaling is applied here — this
+        // keeps the live "outside build volume" highlight in agreement with Print::validate().
+        (void) angle_deg;
+    }
+}
+
 #if 0
 // Tests intersections of projected triangles, not just their vertices against a bounding box.
 // This test also correctly evaluates collision of a non-convex object with the bounding box.
@@ -384,6 +409,11 @@ BuildVolume::ObjectState BuildVolume::object_state(const indexed_triangle_set& i
            build_volume.max.z() = std::numeric_limits<double>::max();
        if (ignore_bottom)
            build_volume.min.z() = -std::numeric_limits<double>::max();
+        // Belt printer: extend Y bounds for infinite Y.
+        if (m_is_belt_printer && m_belt_infinite_y) {
+            build_volume.min.y() = -std::numeric_limits<double>::max();
+            build_volume.max.y() = std::numeric_limits<double>::max();
+        }
        BoundingBox3Base<Vec3f> build_volumef(build_volume.min.cast<float>(), build_volume.max.cast<float>());
        // The following test correctly interprets intersection of a non-convex object with a rectangular build volume.
        //return rectangle_test(its, trafo, to_2d(build_volume.min), to_2d(build_volume.max), build_volume.max.z());
@@ -57,6 +57,10 @@ public:
    // Initialize from PrintConfig::printable_area and PrintConfig::printable_height
    BuildVolume(const std::vector<Vec2d> &printable_area, const double printable_height, const std::vector<std::vector<Vec2d>> &extruder_areas, const std::vector<double>& extruder_printable_heights);

+    // Belt printer configuration.
+    void set_belt_printer(bool enabled, double angle_deg, bool infinite_y);
+    bool is_belt_printer() const { return m_is_belt_printer; }
+
    // Source data, unscaled coordinates.
    const std::vector<Vec2d>&   printable_area()         const { return m_bed_shape; }
    double                      printable_height()  const { return m_max_print_height; }
@@ -80,7 +84,7 @@ public:
    indexed_triangle_set        bounding_mesh(bool scale=true) const;

    // Center of the print bed, unscaled.
-    Vec2d                       bed_center()        const { return to_2d(m_bboxf.center()); }
+    Vec2d                       bed_center()        const { return get_extents(m_bed_shape).center(); }
    // Convex hull of polygon(), scaled.
    const Polygon&              convex_hull()       const { return m_convex_hull; }
    // Smallest enclosing circle of polygon(), scaled.
@@ -139,6 +143,10 @@ private:
    // Source definition of the print volume height (PrintConfig::printable_height)
    double              m_max_print_height { 0.f };
    std::vector<double> m_extruder_printable_height;
+    // Belt printer state.
+    bool                m_is_belt_printer { false };
+    double              m_belt_angle { 0. };
+    bool                m_belt_infinite_y { false };

    // Derived values.
    BuildVolume_Type                m_type { BuildVolume_Type::Invalid };
@@ -79,6 +79,16 @@ set(lisbslic3r_sources
    BoundingBox.hpp
    BridgeDetector.cpp
    BridgeDetector.hpp
+    BeltGCode.cpp
+    BeltGCode.hpp
+    BeltGCodeWriter.cpp
+    BeltGCodeWriter.hpp
+    BeltSliceStrategy.cpp
+    BeltSliceStrategy.hpp
+    BeltTransform.cpp
+    BeltTransform.hpp
+    FirstLayerPlane.cpp
+    FirstLayerPlane.hpp
    Brim.cpp
    BrimEarsPoint.hpp
    Brim.hpp
@@ -209,6 +219,10 @@ set(lisbslic3r_sources
    GCode/AdaptivePAProcessor.hpp
    GCode/AvoidCrossingPerimeters.cpp
    GCode/AvoidCrossingPerimeters.hpp
+    GCode/BeltBackTransform.cpp
+    GCode/BeltBackTransform.hpp
+    GCode/MachineFrameTransform.cpp
+    GCode/MachineFrameTransform.hpp
    GCode/ConflictChecker.cpp
    GCode/ConflictChecker.hpp
    GCode/CoolingBuffer.cpp
@@ -416,6 +430,8 @@ set(lisbslic3r_sources
    SlicingAdaptive.hpp
    Slicing.cpp
    Slicing.hpp
+    Support/BeltFloorContext.cpp
+    Support/BeltFloorContext.hpp
    Support/SupportCommon.cpp
    Support/SupportCommon.hpp
    Support/SupportLayer.hpp
@@ -396,6 +396,11 @@ inline void translate(ExPolygons &expolys, const Point &p) {
        expoly.translate(p);
 }

+inline void translate(Polygons &polys, const Point &p) {
+    for (Polygon &poly : polys)
+        poly.translate(p);
+}
+
 inline void polygons_append(Polygons &dst, const ExPolygon &src) 
 { 
    dst.reserve(dst.size() + src.holes.size() + 1);
@@ -0,0 +1,225 @@
+#include "FirstLayerPlane.hpp"
+#include "BeltTransform.hpp"
+
+#include <algorithm>
+#include <climits>
+#include <cmath>
+
+namespace Slic3r {
+
+namespace {
+
+// Build the row of the gcode-axis-remap matrix R that produces machine_Z,
+// AS A FUNCTION OF a slicing-frame point in the GCode generator's coordinate
+// space.  Without back-transform this is just R.row(2).  With back-transform
+// the writer applies F^-1 before R, so the effective row is (R * F^-1).row(2).
+//
+// Returns a pair (gradient, constant) such that:
+//     machine_Z(p_slicing) = gradient.dot(p_slicing) + constant
+struct MachineZAffine {
+    Vec3d  gradient = Vec3d::UnitZ();
+    double constant = 0.0;
+};
+
+MachineZAffine compute_machine_z_affine(const PrintConfig &config)
+{
+    MachineZAffine out;
+
+    // R is the matrix form of GCodeWriter::apply_axis_remap.  Each output axis
+    // i picks one slicing-frame component (with sign + optional Rev mode
+    // translation) based on m_remap_{x,y,z}.  We only need row 2 (the z output)
+    // since machine_Z is what defines the first-layer plane.
+    int rz = int(config.gcode_remap_z.value);
+    int axis = rz % 3;
+    double sign;
+    double trans;
+    if (rz < int(RemapAxis::NegX)) {            // 0..2 = PosX/Y/Z
+        sign  = 1.0;
+        trans = 0.0;
+    } else if (rz < int(RemapAxis::RevX)) {     // 3..5 = NegX/Y/Z
+        sign  = -1.0;
+        trans = 0.0;
+    } else {                                     // 6..8 = RevX/Y/Z
+        sign = -1.0;
+        BoundingBoxf bbox_bed(config.printable_area.values);
+        Vec3d vol_max(bbox_bed.max.x(),
+                      bbox_bed.max.y(),
+                      config.printable_height.value);
+        trans = vol_max[axis];
+    }
+
+    Vec3d r_row = Vec3d::Zero();
+    r_row[axis] = sign;
+
+    // Without back-transform, machine_Z(slicing) = r_row · slicing + trans.
+    out.gradient = r_row;
+    out.constant = trans;
+
+    if (config.gcode_back_transform.value && config.belt_printer.value) {
+        // BeltGCodeWriter applies F^-1 before R when back-transform is on.
+        // So machine_Z(slicing) = r_row · (F^-1 · slicing) + trans
+        //                       = (r_row^T · F^-1) · slicing + trans
+        // We need to compose r_row with F^-1 from the LEFT (treating r_row as
+        // a row vector).  Eigen makes this easy: it's just F^-1.transpose() * r_row.
+        Transform3d forward = BeltTransformPipeline::build_forward_transform(config);
+        Transform3d inverse = forward.inverse();
+        // Note: forward.translation() is normally zero (per-print transforms
+        // don't add a translation; the per-object z_shift is added separately
+        // in PrintObjectSlice).  We still incorporate inverse.translation() in
+        // case a Rev-mode preslice_remap puts a translation in F.
+        Vec3d composed_grad = inverse.linear().transpose() * r_row;
+        double composed_trans =
+            r_row.dot(inverse.translation()) + trans;
+        out.gradient = composed_grad;
+        out.constant = composed_trans;
+    }
+
+    return out;
+}
+
+} // namespace
+
+FirstLayerPlane::FirstLayerPlane(const PrintConfig &config)
+{
+    // -------- Resolve Auto -------------------------------------------------
+    FirstLayerPlaneMode mode = config.first_layer_plane.value;
+    if (mode == FirstLayerPlaneMode::Auto) {
+        bool belt_affine_active = config.belt_printer.value &&
+            config.belt_slice_rotation.value != BeltRotationAxis::None &&
+            std::abs(config.belt_slice_rotation_angle.value) > EPSILON;
+        mode = belt_affine_active ? FirstLayerPlaneMode::BeltAffine
+                                  : FirstLayerPlaneMode::XY;
+    }
+    m_mode = mode;
+
+    // -------- Band thickness ----------------------------------------------
+    // Note: layer_height lives in PrintObjectConfig, not PrintConfig, so we
+    // can't fall back to it from here.  initial_layer_print_height is in
+    // PrintConfig and is the right default anyway (the legacy first-layer
+    // semantics used initial_layer_print_height, not the regular one).
+    double thickness = config.first_layer_plane_thickness.value;
+    if (thickness <= 0.0)
+        thickness = config.initial_layer_print_height.value;
+    if (thickness <= 0.0)
+        thickness = 0.2;
+    m_thickness_mm = thickness;
+
+    const double user_offset = config.first_layer_plane_offset.value;
+
+    // -------- Build the plane ---------------------------------------------
+    auto set_axis_aligned = [&](const Vec3d &n_unit, double offset_along_n) {
+        m_normal = n_unit;
+        m_offset = offset_along_n;
+    };
+
+    switch (mode) {
+    case FirstLayerPlaneMode::XY:
+        // Legacy XY plane.  Inactive: short-circuit to layer-index path.
+        set_axis_aligned(Vec3d::UnitZ(), user_offset);
+        m_active = false;
+        return;
+
+    case FirstLayerPlaneMode::YZ:
+        set_axis_aligned(Vec3d::UnitX(), user_offset);
+        m_active = true;
+        return;
+
+    case FirstLayerPlaneMode::XZ:
+        set_axis_aligned(Vec3d::UnitY(), user_offset);
+        m_active = true;
+        return;
+
+    case FirstLayerPlaneMode::BeltAffine: {
+        // Compute the slicing-frame plane that maps to machine_Z = user_offset
+        // under the gcode axis remap (and optional back-transform).
+        MachineZAffine mz = compute_machine_z_affine(config);
+        double cmag = mz.gradient.norm();
+        if (cmag < EPSILON) {
+            // Degenerate: slicing point doesn't affect machine_Z.  Fall back.
+            set_axis_aligned(Vec3d::UnitZ(), user_offset);
+            m_active = false;
+            return;
+        }
+        // Plane equation: gradient · slicing = user_offset - constant
+        const double K = user_offset - mz.constant;
+        m_normal = mz.gradient / cmag;
+        m_offset = K / cmag;
+        m_active = true;
+        return;
+    }
+
+    case FirstLayerPlaneMode::Auto:
+        // Should have been resolved above.
+        m_active = false;
+        return;
+    }
+
+    m_active = false;
+}
+
+double FirstLayerPlane::distance_from_plane(const Vec3d &point_slicing_mm) const
+{
+    return m_normal.dot(point_slicing_mm) - m_offset;
+}
+
+bool FirstLayerPlane::is_first_layer(const Vec3d &point_slicing_mm,
+                                     double first_layer_height_mm) const
+{
+    if (!m_active)
+        return false;
+    return distance_from_plane(point_slicing_mm) < first_layer_height_mm;
+}
+
+int FirstLayerPlane::effective_layer_index(const Vec3d &point_slicing_mm) const
+{
+    if (!m_active)
+        return INT_MAX / 2;  // Effectively "way past first layer".
+    double d = distance_from_plane(point_slicing_mm);
+    if (d <= 0.0)
+        return 0;
+    return int(std::floor(d / m_thickness_mm));
+}
+
+int FirstLayerPlane::min_effective_index_for_xy_bbox(
+    const BoundingBoxf &xy_bbox_mm, double slicing_z_mm) const
+{
+    if (!m_active)
+        return INT_MAX / 2;
+    // For the rectangular bbox in (x, y) at fixed z, the smallest value of
+    // (n.x*x + n.y*y + n.z*z - offset) is achieved at one of the four
+    // corners, with the smaller component picked when the corresponding
+    // normal coefficient is positive.
+    const double x_for_min = (m_normal.x() >= 0.0)
+        ? xy_bbox_mm.min.x() : xy_bbox_mm.max.x();
+    const double y_for_min = (m_normal.y() >= 0.0)
+        ? xy_bbox_mm.min.y() : xy_bbox_mm.max.y();
+    const double dmin = m_normal.x() * x_for_min
+                      + m_normal.y() * y_for_min
+                      + m_normal.z() * slicing_z_mm
+                      - m_offset;
+    if (dmin <= 0.0)
+        return 0;
+    return int(std::floor(dmin / m_thickness_mm));
+}
+
+int FirstLayerPlane::min_effective_index_for_bbox3(
+    const BoundingBoxf3 &bbox_mm) const
+{
+    if (!m_active)
+        return INT_MAX / 2;
+    const double x_for_min = (m_normal.x() >= 0.0)
+        ? bbox_mm.min.x() : bbox_mm.max.x();
+    const double y_for_min = (m_normal.y() >= 0.0)
+        ? bbox_mm.min.y() : bbox_mm.max.y();
+    const double z_for_min = (m_normal.z() >= 0.0)
+        ? bbox_mm.min.z() : bbox_mm.max.z();
+    const double dmin = m_normal.x() * x_for_min
+                      + m_normal.y() * y_for_min
+                      + m_normal.z() * z_for_min
+                      - m_offset;
+    if (dmin <= 0.0)
+        return 0;
+    return int(std::floor(dmin / m_thickness_mm));
+}
+
+} // namespace Slic3r
@@ -0,0 +1,76 @@
+#ifndef slic3r_FirstLayerPlane_hpp_
+#define slic3r_FirstLayerPlane_hpp_
+
+#include "libslic3r.h"
+#include "Point.hpp"
+#include "BoundingBox.hpp"
+#include "PrintConfig.hpp"
+
+namespace Slic3r {
+
+// Decides which extrusions get "first layer" treatment (no fan, slow speed,
+// initial-layer accel/jerk, deferred temperature drop) by reference to a
+// configurable plane in slicing-frame coordinates rather than the slicing
+// layer index.
+//
+// On a normal flat-bed printer the plane is XY at slicing_Z = 0 and the
+// evaluator is INACTIVE — every call site short-circuits back to the legacy
+// `Layer::id() == 0` test.  On a belt printer with a Z-from-Y shear the
+// belt surface (machine_Z = 0) maps to a plane in slicing-frame coordinates
+// derived from the gcode axis remap, so layer-index-based detection no
+// longer matches the physical first printed surface.
+//
+// Plane representation: unit normal `n` (slicing frame) and offset along
+// the normal such that the plane equation is `n · p == offset`.  Signed
+// perpendicular distance is `d(p) = n · p - offset`.  Positive distance
+// means "away from the belt surface", negative means "below the plane".
+class FirstLayerPlane
+{
+public:
+    explicit FirstLayerPlane(const PrintConfig &config);
+
+    // Inactive when the legacy XY layer-index path should be used.  This
+    // covers all non-belt printers and any belt printer where the user
+    // explicitly picked XY mode.
+    bool                is_active() const     { return m_active; }
+    FirstLayerPlaneMode effective_mode() const{ return m_mode; }
+    double              band_thickness_mm() const { return m_thickness_mm; }
+    const Vec3d &       normal() const        { return m_normal; }
+    double              plane_offset() const  { return m_offset; }
+
+    // Signed perpendicular distance from a slicing-frame point to the plane.
+    double distance_from_plane(const Vec3d &point_slicing_mm) const;
+
+    // True if perpendicular distance < first_layer_height_mm.  When the
+    // evaluator is inactive this returns false (call sites should fall back
+    // to the legacy per-layer path before reaching this function).
+    bool is_first_layer(const Vec3d &point_slicing_mm,
+                        double first_layer_height_mm) const;
+
+    // floor((distance - 0) / band_thickness), clamped to [0, +inf).  Used
+    // for "first N layers" thresholds (fan, slow_down_layers).  Returns 0
+    // for points within the band.  Returns INT_MAX/2 when inactive.
+    int effective_layer_index(const Vec3d &point_slicing_mm) const;
+
+    // Min effective index over a 2D bbox at a fixed slicing_Z.  Used for
+    // layer-level decisions (e.g. temperature transition gate) where we
+    // don't want to walk every extrusion in the layer.  For axis-aligned
+    // planes this is exact; for tilted planes it's a tight lower bound
+    // (the plane projection of the bbox's extreme corner).
+    int min_effective_index_for_xy_bbox(const BoundingBoxf &xy_bbox_mm,
+                                        double              slicing_z_mm) const;
+
+    // Same as above but the bbox spans a Z range too.
+    int min_effective_index_for_bbox3(const BoundingBoxf3 &bbox_mm) const;
+
+private:
+    bool                m_active        = false;
+    FirstLayerPlaneMode m_mode          = FirstLayerPlaneMode::XY;
+    Vec3d               m_normal        = Vec3d::UnitZ();  // unit, slicing frame
+    double              m_offset        = 0.0;             // n·p == m_offset
+    double              m_thickness_mm  = 0.0;
+};
+
+} // namespace Slic3r
+
+#endif // slic3r_FirstLayerPlane_hpp_
@@ -4,6 +4,8 @@
 #include "libslic3r.h"
 #include "ExPolygon.hpp"
 #include "GCodeWriter.hpp"
+#include "BeltGCodeWriter.hpp"
+#include "FirstLayerPlane.hpp"
 #include "Layer.hpp"
 #include "Point.hpp"
 #include "PlaceholderParser.hpp"
@@ -206,16 +208,18 @@ public:
        m_last_obj_copy(nullptr, Point(std::numeric_limits<coord_t>::max(), std::numeric_limits<coord_t>::max())),
        // BBS
        m_toolchange_count(0),
-        m_nominal_z(0.)
+        m_nominal_z(0.),
+        m_writer(std::make_unique<GCodeWriter>())
        {}
-    ~GCode() = default;
+    virtual ~GCode() = default;

+public:
    // throws std::runtime_exception on error,
    // throws CanceledException through print->throw_if_canceled().
    void            do_export(Print* print, const char* path, GCodeProcessorResult* result = nullptr, ThumbnailsGeneratorCallback thumbnail_cb = nullptr);
    void            export_layer_filaments(GCodeProcessorResult* result);
    //BBS: set offset for gcode writer
-    void set_gcode_offset(double x, double y) { m_writer.set_xy_offset(x, y); m_processor.set_xy_offset(x, y);}
+    void set_gcode_offset(double x, double y) { m_writer->set_xy_offset(x, y); m_processor.set_xy_offset(x, y);}

    // Exported for the helper classes (OozePrevention, Wipe) and for the Perl binding for unit tests.
    const Vec2d&    origin() const { return m_origin; }
@@ -229,8 +233,8 @@ public:
    Vec3d                    point_to_gcode_quantized(const Point3& point) const;
    const FullPrintConfig &config() const { return m_config; }
    const Layer*    layer() const { return m_layer; }
-    GCodeWriter&    writer() { return m_writer; }
-    const GCodeWriter& writer() const { return m_writer; }
+    GCodeWriter&    writer() { return *m_writer; }
+    const GCodeWriter& writer() const { return *m_writer; }
    PlaceholderParser& placeholder_parser() { return m_placeholder_parser_integration.parser; }
    const PlaceholderParser& placeholder_parser() const { return m_placeholder_parser_integration.parser; }
    // Process a template through the placeholder parser, collect error messages to be reported
@@ -252,7 +256,7 @@ public:
    std::string     travel_to(const Point& point, ExtrusionRole role, std::string comment, double z = DBL_MAX);
    bool            needs_retraction(const Polyline& travel, ExtrusionRole role, LiftType& lift_type);
    std::string     retract(bool toolchange = false, bool is_last_retraction = false, LiftType lift_type = LiftType::NormalLift, bool apply_instantly = false, ExtrusionRole role = erNone);
-    std::string     unretract() { return m_writer.unlift() + m_writer.unretract(); }
+    std::string     unretract() { return m_writer->unlift() + m_writer->unretract(); }
    std::string     set_extruder(unsigned int extruder_id, double print_z, bool by_object=false, int toolchange_temp_override = -1);
    bool is_BBL_Printer();
    WipeTowerType wipe_tower_type();
@@ -304,7 +308,15 @@ public:
        }
    };

-private:
+    // Public accessor for the first-layer plane evaluator.  Used by
+    // CoolingBuffer (which is constructed with a GCode reference and needs
+    // to read the plane for per-segment fan re-evaluation).  All other
+    // first-layer-plane access points (on_first_layer overload, effective
+    // index helper) are in the protected section since they're called from
+    // GCode internals only.
+    const FirstLayerPlane *first_layer_plane() const { return m_first_layer_plane.get(); }
+
+protected:
    class GCodeOutputStream {
    public:
        GCodeOutputStream(FILE *f, GCodeProcessor &processor) : f(f), m_processor(processor) {}
@@ -332,9 +344,17 @@ private:
        FILE *f = nullptr;
        GCodeProcessor &m_processor;
    };
+
+    // Virtual hooks for belt printer subclass (BeltGCode).
+    // No-ops in base GCode; overridden in BeltGCode.
+    virtual void init_belt_writer(Print &print, bool is_bbl_printers) {}
+    virtual void write_belt_header(GCodeOutputStream &file, const Print &print) {}
+    virtual void on_set_origin(const PrintObject *obj, const Point &inst_shift) {}
+    virtual bool should_disable_arc_fitting() const { return false; }
+
    void            _do_export(Print &print, GCodeOutputStream &file, ThumbnailsGeneratorCallback thumbnail_cb);

-    static std::vector<LayerToPrint>        		                   collect_layers_to_print(const PrintObject &object);
+    static std::vector<LayerToPrint>        		                   collect_layers_to_print(const PrintObject &object, bool skip_empty_first_layer = false);
    static std::vector<std::pair<coordf_t, std::vector<LayerToPrint>>> collect_layers_to_print(const Print &print);

    std::string generate_skirt(const Print &print,
@@ -518,7 +538,7 @@ private:
    DynamicConfig                       m_calib_config;
    // scaled G-code resolution
    double                              m_scaled_resolution;
-    GCodeWriter                         m_writer;
+    std::unique_ptr<GCodeWriter>         m_writer;

    struct PlaceholderParserIntegration {
        void reset();
@@ -609,6 +629,11 @@ private:

    std::unique_ptr<CoolingBuffer>      m_cooling_buffer;
    std::unique_ptr<SpiralVase>         m_spiral_vase;
+    // First-layer plane evaluator.  Constructed once per print from the
+    // PrintConfig.  is_active() == false on non-belt printers and on belt
+    // printers without a Z-axis shear; in that case all per-path plane
+    // checks short-circuit to the legacy Layer::id() == 0 path.
+    std::unique_ptr<FirstLayerPlane>    m_first_layer_plane;

    std::unique_ptr<PressureEqualizer>  m_pressure_equalizer;
    
@@ -668,6 +693,25 @@ private:
    // On the first printing layer. This flag triggers first layer speeds.
    //BBS
    bool    on_first_layer() const { return m_layer != nullptr && m_layer->id() == 0 && abs(m_layer->bottom_z()) < EPSILON; }
+    // Per-point first-layer test.  When the FirstLayerPlane evaluator is
+    // active, the result depends on the supplied slicing-frame point;
+    // otherwise we delegate to the legacy per-layer test.  This is the
+    // entry point used by per-path call sites in _extrude.
+    bool on_first_layer(const Vec3d &point_slicing_mm) const {
+        if (m_first_layer_plane && m_first_layer_plane->is_active())
+            return m_first_layer_plane->is_first_layer(
+                point_slicing_mm, m_config.initial_layer_print_height.value);
+        return on_first_layer();
+    }
+    // "Effective layer index" used to drive layer-count thresholds like
+    // slow_down_layers.  When the evaluator is active this returns the
+    // perpendicular distance to the plane in band_thickness_mm units;
+    // otherwise it returns the legacy slicing layer index.
+    int effective_layer_index_for_point(const Vec3d &point_slicing_mm) const {
+        if (m_first_layer_plane && m_first_layer_plane->is_active())
+            return m_first_layer_plane->effective_layer_index(point_slicing_mm);
+        return on_first_layer() ? 0 : layer_id();
+    }
    int layer_id() const {
        if (m_layer == nullptr)
            return -1;
@@ -0,0 +1,40 @@
+#include "BeltBackTransform.hpp"
+#include "../BeltTransform.hpp"
+
+namespace Slic3r {
+
+bool BeltBackTransform::init_from_config(const PrintConfig &config)
+{
+    m_active  = false;
+    m_inverse = Transform3d::Identity();
+
+    if (!config.belt_printer.value || !config.gcode_back_transform.value)
+        return false;
+
+    // Require at least one active transform to proceed.
+    bool has_global_rotation = config.belt_slice_rotation_global.value
+                            && config.belt_slice_rotation.value != BeltRotationAxis::None;
+    bool has_preslice_global = config.belt_preslice_global.value
+                            || config.preslice_remap_global.value;
+    if (!has_global_rotation && !has_preslice_global
+        && !BeltTransformPipeline::has_preslice_remap(config))
+        return false;
+
+    // Build the forward pipeline (rotation * pre_remap) and store its inverse.
+    Transform3d forward = BeltTransformPipeline::build_forward_transform(config);
+    if (forward.isApprox(Transform3d::Identity()))
+        return false;
+
+    m_inverse = forward.inverse();
+    m_active  = true;
+    return true;
+}
+
+Vec3d BeltBackTransform::apply(const Vec3d &pos) const
+{
+    if (!m_active)
+        return pos;
+    return m_inverse * pos;
+}
+
+} // namespace Slic3r
@@ -0,0 +1,45 @@
+#ifndef slic3r_BeltBackTransform_hpp_
+#define slic3r_BeltBackTransform_hpp_
+
+#include "../libslic3r.h"
+#include "../Point.hpp"
+#include "../PrintConfig.hpp"
+
+namespace Slic3r {
+
+// Reverses the pre-slice remap + shear + scale transforms that
+// PrintObjectSlice.cpp applies to belt printer geometry, converting G-code
+// coordinates from the sliced (remapped/sheared/scaled) frame back to the
+// machine's real coordinate space.
+//
+// Initialized once from PrintConfig, then applied per-point in
+// GCodeWriter::to_machine_coords() before axis remapping.
+//
+// Active when gcode_back_transform is true AND at least one of:
+//   - a shear axis has global mode enabled, or
+//   - a pre-slice axis remap is non-identity.
+class BeltBackTransform
+{
+public:
+    BeltBackTransform() = default;
+
+    // Initialize from belt printer config.  Rebuilds the same pre-slice remap,
+    // shear, and scale matrices as PrintObjectSlice.cpp and precomputes the
+    // affine inverse.  Returns true if a non-identity back-transform was computed.
+    bool init_from_config(const PrintConfig &config);
+
+    // Apply the inverse transform to a point.  Returns pos unchanged if
+    // no back-transform is active.
+    Vec3d apply(const Vec3d &pos) const;
+
+    // True if a non-identity back-transform is active.
+    bool is_active() const { return m_active; }
+
+private:
+    bool       m_active  = false;
+    Transform3d m_inverse = Transform3d::Identity();
+};
+
+} // namespace Slic3r
+
+#endif // slic3r_BeltBackTransform_hpp_
@@ -1,10 +1,14 @@
 #include "../GCode.hpp"
+#include "../FirstLayerPlane.hpp"
 #include "CoolingBuffer.hpp"
 #include <boost/algorithm/string/predicate.hpp>
 #include <boost/algorithm/string/replace.hpp>
 #include <boost/log/trivial.hpp>
+#include <algorithm>
+#include <cstdlib>
 #include <iostream>
 #include <float.h>
+#include <string_view>
 #include <system_error>
 #include <unordered_map>

@@ -28,6 +32,12 @@ CoolingBuffer::CoolingBuffer(GCode &gcodegen) : m_config(gcodegen.config()), m_t
        m_num_extruders = std::max(ex.id() + 1, m_num_extruders);
        m_extruder_ids.emplace_back(ex.id());
    }
+
+    // Borrow the first-layer plane from the GCode generator.  When inactive
+    // (non-belt printers and belt printers without Z shear), per-line fan
+    // re-evaluation is skipped and behavior is bit-identical to the legacy
+    // per-layer path.
+    m_first_layer_plane = gcodegen.first_layer_plane();
 }

 void CoolingBuffer::reset(const Vec3d &position)
@@ -328,6 +338,13 @@ std::string CoolingBuffer::process_layer(std::string &&gcode, size_t layer_id, b
        std::vector<PerExtruderAdjustments> per_extruder_adjustments = this->parse_layer_gcode(m_gcode, m_current_pos);
        float layer_time_stretched = this->calculate_layer_slowdown(per_extruder_adjustments);
        out = this->apply_layer_cooldown(m_gcode, layer_id, layer_time_stretched, per_extruder_adjustments);
+        // First-layer plane: per-segment fan re-evaluation post-pass.  Walks
+        // the cooled-down gcode and inserts inline M106 commands at band
+        // crossings (where the path's perpendicular distance to the plane
+        // crosses close_fan_the_first_x_layers thresholds).  No-op when
+        // the evaluator is inactive.
+        if (m_first_layer_plane && m_first_layer_plane->is_active())
+            out = this->apply_first_layer_plane_fan_eval(std::move(out), layer_id, layer_time_stretched);
        m_gcode.clear();
    }
    return out;
@@ -1014,4 +1031,214 @@ std::string CoolingBuffer::apply_layer_cooldown(
    return new_gcode;
 }

+// Pure helper: compute the main fan speed for a given effective layer index.
+// Mirrors the inline logic in change_extruder_set_fan but is callable from
+// per-line code in apply_first_layer_plane_fan_eval.
+int CoolingBuffer::compute_main_fan_speed(int effective_layer_id, float layer_time,
+                                           unsigned int extruder_id) const
+{
+#define EXTRUDER_CFG(opt) m_config.opt.get_at(extruder_id)
+    float fan_min_speed              = EXTRUDER_CFG(fan_min_speed);
+    float fan_max_speed              = EXTRUDER_CFG(fan_max_speed);
+    bool  reduce_fan_stop_start_freq = EXTRUDER_CFG(reduce_fan_stop_start_freq);
+    int   close_fan_the_first_x_layers = EXTRUDER_CFG(close_fan_the_first_x_layers);
+    int   full_fan_speed_layer       = EXTRUDER_CFG(full_fan_speed_layer);
+    float slow_down_layer_time       = float(EXTRUDER_CFG(slow_down_layer_time));
+    float fan_cooling_layer_time     = float(EXTRUDER_CFG(fan_cooling_layer_time));
+#undef EXTRUDER_CFG
+
+    if (close_fan_the_first_x_layers <= 0 && full_fan_speed_layer > 0)
+        close_fan_the_first_x_layers = 1;
+
+    float fan_speed_new = reduce_fan_stop_start_freq ? fan_min_speed : 0.f;
+    if (effective_layer_id >= close_fan_the_first_x_layers) {
+        if (layer_time < slow_down_layer_time) {
+            fan_speed_new = fan_max_speed;
+        } else if (layer_time < fan_cooling_layer_time) {
+            double t = (layer_time - slow_down_layer_time) /
+                       (fan_cooling_layer_time - slow_down_layer_time);
+            fan_speed_new = float(int(floor(t * fan_min_speed +
+                                            (1. - t) * fan_max_speed) + 0.5));
+        }
+        if (effective_layer_id + 1 < full_fan_speed_layer) {
+            float factor = float(effective_layer_id + 1 - close_fan_the_first_x_layers)
+                         / float(full_fan_speed_layer - close_fan_the_first_x_layers);
+            fan_speed_new = float(std::clamp(int(fan_speed_new * factor + 0.5f), 0, 255));
+        }
+    } else {
+        fan_speed_new = 0.f;
+    }
+    return int(fan_speed_new);
+}
+
+// Post-pass: walk the cooled-down gcode line by line, track XYZ position,
+// and insert M106 commands at first-layer-plane band crossings so the fan
+// follows perpendicular distance to the plane rather than the slicing-layer
+// index.  Only invoked when the FirstLayerPlane evaluator is active.
+//
+// This implementation is intentionally minimal: it overrides only the MAIN
+// fan (the one set by GCodeWriter::set_fan); overhang/internal-bridge/etc
+// special fans remain at their layer-level values from apply_layer_cooldown.
+// That keeps the per-line logic small while still giving the user precise
+// fan control near the belt surface, which is the main quality concern.
+std::string CoolingBuffer::apply_first_layer_plane_fan_eval(
+    std::string &&gcode_in, size_t /*layer_id*/, float layer_time)
+{
+    if (!m_first_layer_plane || !m_first_layer_plane->is_active())
+        return std::move(gcode_in);
+
+    const std::string &gcode = gcode_in;
+    std::string out;
+    out.reserve(gcode.size() + 256);
+
+    // Match the PWM floor applied at every other set_fan call in this file so
+    // band-crossing M106 emissions start the fan reliably at low speeds.
+    const unsigned int part_cooling_fan_min_pwm = static_cast<unsigned int>(std::max(0, m_config.part_cooling_fan_min_pwm.value));
+
+    // Track position in slicing-frame mm.  Seed from m_current_pos which the
+    // CoolingBuffer keeps up-to-date across layers.
+    Vec3d cur_pos_mm(m_current_pos[0], m_current_pos[1], m_current_pos[2]);
+
+    // Track current main fan speed by parsing M106 commands as we walk so
+    // we can restore it after a band exit.
+    int  current_main_fan = m_fan_speed;
+    int  pre_band_main_fan = current_main_fan;
+    // Implicit initial state: assume the layer started "out of the band"
+    // (i.e., the layer-level fan setting from apply_layer_cooldown is in
+    // effect).  The first movement we encounter will reconcile this.
+    bool in_first_layer_band = false;
+    unsigned int active_extruder = m_current_extruder;
+
+    auto parse_xyz_into = [](const std::string_view &line_sv, Vec3d &p) {
+        if (line_sv.size() < 3) return false;
+        if (line_sv[0] != 'G') return false;
+        if (line_sv[1] != '0' && line_sv[1] != '1') return false;
+        if (line_sv[2] != ' ' && line_sv[2] != '\t') return false;
+        const char *c   = line_sv.data() + 3;
+        const char *end = line_sv.data() + line_sv.size();
+        bool        any = false;
+        while (c < end && *c != ';') {
+            while (c < end && (*c == ' ' || *c == '\t')) ++c;
+            if (c >= end || *c == ';' || *c == '\n' || *c == '\r') break;
+            char axis = *c;
+            ++c;
+            if (axis == 'X' || axis == 'Y' || axis == 'Z') {
+                char *next;
+                double v = std::strtod(c, &next);
+                if (next != c) {
+                    if (axis == 'X') p.x() = v;
+                    else if (axis == 'Y') p.y() = v;
+                    else                  p.z() = v;
+                    c   = next;
+                    any = true;
+                    continue;
+                }
+            }
+            // Skip unrecognized word.
+            while (c < end && *c != ' ' && *c != '\t' && *c != ';' && *c != '\n')
+                ++c;
+        }
+        return any;
+    };
+
+    auto parse_m106 = [](const std::string_view &line_sv) -> int {
+        // Returns -1 if not an M106, otherwise the S value (0..255).
+        if (line_sv.size() < 4 || line_sv[0] != 'M') return -1;
+        if (!(line_sv[1] == '1' && line_sv[2] == '0' && line_sv[3] == '6'))
+            return -1;
+        // Find S<value>
+        size_t s_pos = line_sv.find('S');
+        if (s_pos == std::string_view::npos) return -1;
+        const char *c = line_sv.data() + s_pos + 1;
+        char *next;
+        long v = std::strtol(c, &next, 10);
+        if (next == c) return -1;
+        return int(std::clamp<long>(v, 0, 255));
+    };
+
+    auto parse_m107 = [](const std::string_view &line_sv) -> bool {
+        return line_sv.size() >= 4 && line_sv[0] == 'M' &&
+               line_sv[1] == '1' && line_sv[2] == '0' && line_sv[3] == '7';
+    };
+
+    auto parse_tool_change = [this](const std::string_view &line_sv) -> int {
+        // Returns the new extruder id, or -1 if not a toolchange.
+        if (line_sv.size() < m_toolchange_prefix.size() + 1) return -1;
+        if (line_sv.compare(0, m_toolchange_prefix.size(), m_toolchange_prefix) != 0)
+            return -1;
+        const char *c = line_sv.data() + m_toolchange_prefix.size();
+        char *next;
+        long v = std::strtol(c, &next, 10);
+        if (next == c) return -1;
+        return int(v);
+    };
+
+    const char *p   = gcode.c_str();
+    const char *end = gcode.c_str() + gcode.size();
+    while (p < end) {
+        const char *line_end = p;
+        while (line_end < end && *line_end != '\n') ++line_end;
+        const char *next_line = line_end;
+        if (next_line < end) ++next_line;  // include the '\n'
+
+        std::string_view line_sv(p, line_end - p);
+
+        // Track tool changes so the per-line fan eval uses the right extruder.
+        int new_tool = parse_tool_change(line_sv);
+        if (new_tool >= 0)
+            active_extruder = unsigned(new_tool);
+
+        // Track existing fan commands so we can restore the right value when
+        // exiting a band.
+        int m106_speed = parse_m106(line_sv);
+        if (m106_speed >= 0) {
+            current_main_fan = m106_speed;
+            if (!in_first_layer_band)
+                pre_band_main_fan = m106_speed;
+        } else if (parse_m107(line_sv)) {
+            current_main_fan = 0;
+            if (!in_first_layer_band)
+                pre_band_main_fan = 0;
+        }
+
+        // Movement line: parse XYZ, evaluate plane, possibly emit a fan
+        // change BEFORE this line.
+        bool moved = parse_xyz_into(line_sv, cur_pos_mm);
+        if (moved) {
+            const int eff_idx = m_first_layer_plane->effective_layer_index(cur_pos_mm);
+            const int close_n = m_config.close_fan_the_first_x_layers.get_at(active_extruder);
+            const bool now_in_band = eff_idx < std::max(close_n, 1);
+            if (now_in_band != in_first_layer_band) {
+                // Band crossing: emit a M106 with the appropriate speed.
+                int target_fan;
+                if (now_in_band) {
+                    // Entering the first-layer band: fan off.
+                    pre_band_main_fan = current_main_fan;
+                    target_fan = compute_main_fan_speed(eff_idx, layer_time, active_extruder);
+                } else {
+                    // Exiting the band: restore the layer's normal fan speed.
+                    // Use compute_main_fan_speed with the effective index so
+                    // the linear ramp factor (close_fan→full_fan_speed_layer)
+                    // also follows distance from the plane.
+                    target_fan = compute_main_fan_speed(eff_idx, layer_time, active_extruder);
+                    if (target_fan == 0)
+                        target_fan = pre_band_main_fan;
+                }
+                if (target_fan != current_main_fan) {
+                    out += GCodeWriter::set_fan(m_config.gcode_flavor, target_fan, part_cooling_fan_min_pwm);
+                    current_main_fan = target_fan;
+                    m_fan_speed = target_fan;
+                    m_current_fan_speed = target_fan;
+                }
+                in_first_layer_band = now_in_band;
+            }
+        }
+
+        out.append(p, next_line - p);
+        p = next_line;
+    }
+
+    return out;
+}
+
 } // namespace Slic3r
@@ -10,6 +10,7 @@ namespace Slic3r {

 class GCode;
 class Layer;
+class FirstLayerPlane;
 struct PerExtruderAdjustments;

 // A standalone G-code filter, to control cooling of the print.
@@ -18,7 +19,7 @@ struct PerExtruderAdjustments;
 //
 // The simple it sounds, the actual implementation is significantly more complex.
 // Namely, for a multi-extruder print, each material may require a different cooling logic.
-// For example, some materials may not like to print too slowly, while with some materials 
+// For example, some materials may not like to print too slowly, while with some materials
 // we may slow down significantly.
 //
 class CoolingBuffer {
@@ -36,6 +37,21 @@ private:
    // Returns the adjusted G-code.
    std::string apply_layer_cooldown(const std::string &gcode, size_t layer_id, float layer_time, std::vector<PerExtruderAdjustments> &per_extruder_adjustments);

+    // First-layer plane: per-line fan re-evaluation post-pass.  Walks the
+    // post-cooldown gcode, tracks XYZ position, and inserts M106 commands at
+    // band-crossing transitions in slicing-frame coordinates.  Only runs
+    // when m_first_layer_plane is active.
+    std::string apply_first_layer_plane_fan_eval(std::string &&gcode_in,
+                                                  size_t        layer_id,
+                                                  float         layer_time);
+
+    // Pure helper: compute the main fan speed for a given effective layer
+    // index (layer-id units, mapped through the plane evaluator) and the
+    // current extruder.  Mirrors the inline logic in the change_extruder_set_fan
+    // lambda but is callable from per-line code.
+    int compute_main_fan_speed(int effective_layer_id, float layer_time,
+                               unsigned int extruder_id) const;
+
    // G-code snippet cached for the support layers preceding an object layer.
    std::string                 m_gcode;
    // Internal data.
@@ -57,6 +73,9 @@ private:
    unsigned int                m_current_extruder;
    //BBS: current fan speed
    int                         m_current_fan_speed;
+    // First-layer plane evaluator, borrowed from GCode.  Null = inactive
+    // (legacy per-layer fan control).
+    const FirstLayerPlane      *m_first_layer_plane = nullptr;
 };

 }
@@ -3072,6 +3072,44 @@ void GCodeProcessor::process_tags(const std::string_view comment, bool producers
        return;
    }

+    // Belt printer: derive the physical tilt magnitude from the slicing-rotation
+    // angle header comment (used to enable the preview's belt view).
+    if (boost::starts_with(comment, " belt_slice_rotation_angle = ")) {
+        try {
+            m_result.belt_tilt_angle = std::abs(std::stof(std::string(comment.substr(29))));
+        } catch (...) {}
+        return;
+    }
+    // Belt printer: parse pre-slice axis remap from header comments.
+    {
+        auto trim = [](const std::string &s) -> std::string {
+            size_t start = s.find_first_not_of(" \t\r\n");
+            size_t end   = s.find_last_not_of(" \t\r\n");
+            return (start == std::string::npos) ? "" : s.substr(start, end - start + 1);
+        };
+        // Pre-slice axis remap
+        auto parse_remap_axis = [](const std::string &s) -> RemapAxis {
+            if (s == "pos_x") return RemapAxis::PosX;
+            if (s == "pos_y") return RemapAxis::PosY;
+            if (s == "pos_z") return RemapAxis::PosZ;
+            if (s == "neg_x") return RemapAxis::NegX;
+            if (s == "neg_y") return RemapAxis::NegY;
+            if (s == "neg_z") return RemapAxis::NegZ;
+            if (s == "rev_x") return RemapAxis::RevX;
+            if (s == "rev_y") return RemapAxis::RevY;
+            if (s == "rev_z") return RemapAxis::RevZ;
+            return RemapAxis::PosX;
+        };
+        if (boost::starts_with(comment, " preslice_remap_x = ")) {
+            m_result.preslice_remap_x = parse_remap_axis(trim(std::string(comment.substr(25)))); return;
+        }
+        if (boost::starts_with(comment, " preslice_remap_y = ")) {
+            m_result.preslice_remap_y = parse_remap_axis(trim(std::string(comment.substr(25)))); return;
+        }
+        if (boost::starts_with(comment, " preslice_remap_z = ")) {
+            m_result.preslice_remap_z = parse_remap_axis(trim(std::string(comment.substr(25)))); return;
+        }
+    }
    // wipe start tag
    if (boost::starts_with(comment, reserved_tag(ETags::Wipe_Start))) {
        m_wiping = true;
@@ -4895,6 +4933,13 @@ void GCodeProcessor::process_G92(const GCodeReader::GCodeLine& line)
    if (line.has_z()) {
        m_origin[Z] = m_end_position[Z] - line.z() * lengths_scale_factor;
        any_found = true;
+        // Belt only: the start G-code's purge-blob advance + G92 Z0 resets leave a constant
+        // machine-Z origin offset here; the designed-view back-transform subtracts it so
+        // toolpaths map to the model's belt coordinate (gcode Z). Gated on belt_tilt_angle
+        // (set from the belt header, parsed before the body) so non-belt G-code processing
+        // is byte-identical — no unconditional work on the shared path.
+        if (m_result.belt_tilt_angle != 0.f)
+            m_result.belt_z_origin = m_origin[Z];
    }

    if (line.has_e()) {
@@ -245,6 +245,17 @@ class Print;
        bool support_traditional_timelapse{true};
        float printable_height;
        float z_offset;
+        // Belt printer: physical tilt magnitude (deg) parsed from the slicing-rotation
+        // header comment; used to enable the preview's belt view.
+        float belt_tilt_angle{ 0.f };
+        // Belt printer: machine-Z origin offset (mm) left in m_origin[Z] by the start
+        // G-code (purge-blob belt advance + G92 Z0 resets). Move positions are stored
+        // as gcode_Z + this offset, so the designed-view back-transform must subtract it
+        // to recover the model's belt coordinate.
+        float belt_z_origin{ 0.f };
+        RemapAxis preslice_remap_x{ RemapAxis::PosX };
+        RemapAxis preslice_remap_y{ RemapAxis::PosY };
+        RemapAxis preslice_remap_z{ RemapAxis::PosZ };
        SettingsIds settings_ids;
        size_t filaments_count;
        bool backtrace_enabled;
@@ -310,6 +321,11 @@ class Print;
            optimal_assignment = other.optimal_assignment;
            filament_change_count_map = other.filament_change_count_map;
            initial_layer_time = other.initial_layer_time;
+            belt_tilt_angle = other.belt_tilt_angle;
+            belt_z_origin = other.belt_z_origin;
+            preslice_remap_x = other.preslice_remap_x;
+            preslice_remap_y = other.preslice_remap_y;
+            preslice_remap_z = other.preslice_remap_z;
 #if ENABLE_GCODE_VIEWER_STATISTICS
            time = other.time;
 #endif
@@ -0,0 +1,74 @@
+#include "MachineFrameTransform.hpp"
+#include "../Geometry.hpp"
+
+#include <cmath>
+
+namespace Slic3r {
+
+bool MachineFrameTransform::init_from_config(const PrintConfig &config)
+{
+    m_active    = false;
+    m_transform = Transform3d::Identity();
+
+    if (!config.belt_printer.value)
+        return false;
+
+    // The machine-frame transform is derived from the single belt tilt (axis +
+    // angle) that also drives the pre-slice mesh rotation.  Expert decouple lets
+    // the machine-frame angle differ from the slicing rotation; otherwise both
+    // use belt_slice_rotation_angle.
+    const BeltRotationAxis axis = config.belt_slice_rotation.value;
+    if (axis == BeltRotationAxis::None || axis == BeltRotationAxis::Z)
+        return false; // Z is an in-plane spin: no machine-frame tilt.
+
+    const double angle_deg = config.belt_frame_tilt_decouple.value
+        ? config.belt_frame_tilt_angle.value
+        : config.belt_slice_rotation_angle.value;
+    if (std::abs(angle_deg) <= EPSILON)
+        return false;
+
+    const double angle_rad = Geometry::deg2rad(angle_deg);
+    const double cos_a      = std::cos(angle_rad);
+    if (std::abs(cos_a) <= EPSILON)
+        return false;
+    const double tan_a   = std::sin(angle_rad) / cos_a;
+    const double inv_cos = 1.0 / cos_a;
+
+    // Couple the height axis (Z) to the belt-feed axis and stretch the belt-feed
+    // axis by 1/cos so a unit slicing move maps to the correct belt travel.  The
+    // shear sign matches the belt-floor slope derived from the same rotation in
+    // BeltTransformPipeline::compute_belt_height_and_floor:
+    //   tilt about X: feed axis Y, Z += +tan·Y, scale Y *= 1/cos
+    //   tilt about Y: feed axis X, Z += -tan·X, scale X *= 1/cos
+    Matrix3d shear = Matrix3d::Identity();
+    Matrix3d scale = Matrix3d::Identity();
+    if (axis == BeltRotationAxis::X) {
+        shear(2, 1) =  tan_a;   // Z from Y
+        scale(1, 1) =  inv_cos; // Y
+    } else { // BeltRotationAxis::Y
+        shear(2, 0) = -tan_a;   // Z from X
+        scale(0, 0) =  inv_cos; // X
+    }
+
+    // Apply shear first, then scale (the historical default ShearThenScale order:
+    // result = scale * shear * p).  For the canonical 45°/X belt this maps
+    // (x,y,z) -> (x, y/cos, y + z), matching the previous per-axis config.
+    Transform3d combined = Transform3d::Identity();
+    combined.linear() = scale * shear;
+
+    if (combined.isApprox(Transform3d::Identity()))
+        return false;
+
+    m_transform = combined;
+    m_active    = true;
+    return true;
+}
+
+Vec3d MachineFrameTransform::apply(const Vec3d &pos) const
+{
+    if (!m_active)
+        return pos;
+    return m_transform * pos;
+}
+
+} // namespace Slic3r
@@ -0,0 +1,48 @@
+#ifndef slic3r_MachineFrameTransform_hpp_
+#define slic3r_MachineFrameTransform_hpp_
+
+#include "../libslic3r.h"
+#include "../Point.hpp"
+#include "../PrintConfig.hpp"
+
+namespace Slic3r {
+
+// Post-stage machine-frame transform for belt printers.
+//
+// Applied in BeltGCodeWriter::to_machine_coords AFTER the back-transform and
+// the gcode_remap_* axis remap.  Maps Cartesian (axis-permuted) G-code
+// coordinates into the printer's physical machine frame.
+//
+// Derived entirely from the single belt tilt (belt_slice_rotation axis +
+// belt_slice_rotation_angle): a shear coupling the height axis to the belt-feed
+// axis (factor tan a) plus a 1/cos a scale on the belt-feed axis.  The expert
+// belt_frame_tilt_decouple flag lets the machine-frame angle differ from the
+// pre-slice rotation angle via belt_frame_tilt_angle.
+class MachineFrameTransform
+{
+public:
+    MachineFrameTransform() = default;
+
+    // Initialize from belt printer config.  Returns true if a non-identity
+    // transform was computed.  Inactive when belt_printer is disabled or
+    // both shear and scale are identity.
+    bool init_from_config(const PrintConfig &config);
+
+    // Apply the transform to a point.  Returns pos unchanged if not active.
+    Vec3d apply(const Vec3d &pos) const;
+
+    bool is_active() const { return m_active; }
+
+    // The composed shear*scale transform (identity when inactive). Exposed so the
+    // G-code viewer can build the machine->model back-transform for the upright
+    // ("designed") belt preview.
+    const Transform3d& transform() const { return m_transform; }
+
+private:
+    bool        m_active    = false;
+    Transform3d m_transform = Transform3d::Identity();
+};
+
+} // namespace Slic3r
+
+#endif // slic3r_MachineFrameTransform_hpp_
@@ -1,5 +1,6 @@
 #include "GCodeWriter.hpp"
 #include "CustomGCode.hpp"
+#include "Geometry.hpp"
 #include "I18N.hpp"
 #include "PrintConfig.hpp"
 #include <algorithm>
@@ -20,6 +21,36 @@ namespace Slic3r {

 bool GCodeWriter::full_gcode_comment = true;

+void GCodeWriter::set_axis_remap(int rx, int ry, int rz)
+{
+    m_remap_x = rx;
+    m_remap_y = ry;
+    m_remap_z = rz;
+}
+
+void GCodeWriter::set_build_volume_max(const Vec3d &max)
+{
+    m_build_vol_max = max;
+}
+
+bool GCodeWriter::has_axis_remap() const
+{
+    return m_remap_x != 0 || m_remap_y != 1 || m_remap_z != 2;
+}
+
+Vec3d GCodeWriter::apply_axis_remap(const Vec3d &pos) const
+{
+    if (!has_axis_remap())
+        return pos;
+    auto remap = [this, &pos](int r) -> double {
+        int axis = r % 3;
+        if (r < 3) return pos[axis];
+        if (r < 6) return -pos[axis];
+        return m_build_vol_max[axis] - pos[axis];
+    };
+    return { remap(m_remap_x), remap(m_remap_y), remap(m_remap_z) };
+}
+
 bool GCodeWriter::supports_separate_travel_acceleration(GCodeFlavor flavor)
 {
    return (flavor == gcfRepetier || flavor == gcfMarlinFirmware ||  flavor == gcfRepRapFirmware);
@@ -608,7 +639,13 @@ std::string GCodeWriter::travel_to_xy(const Vec2d &point, const std::string &com
    Vec2d point_on_plate = { point(0) - m_x_offset, point(1) - m_y_offset };

    GCodeG1Formatter w;
-    w.emit_xy(point_on_plate);
+    if (has_axis_remap()) {
+        // Axis remap may couple XY with Z; emit full XYZ in machine coordinates.
+        Vec3d machine = apply_axis_remap(Vec3d(point_on_plate.x(), point_on_plate.y(), m_pos.z()));
+        w.emit_xyz(machine);
+    } else {
+        w.emit_xy(point_on_plate);
+    }
    auto speed = m_is_first_layer
        ? this->config.get_abs_value("initial_layer_travel_speed") : this->config.travel_speed.value;
    w.emit_f(speed * 60.0);
@@ -648,8 +685,9 @@ std::string GCodeWriter::lazy_lift(LiftType lift_type, bool spiral_vase)
 }

 // BBS: immediately execute an undelayed lift move with a spiral lift pattern
-// designed specifically for subsequent gcode injection (e.g. timelapse) 
+// designed specifically for subsequent gcode injection (e.g. timelapse)
 std::string GCodeWriter::eager_lift(const LiftType type) {
+    const LiftType effective_type = type;
    std::string lift_move;
    double target_lift = 0;
    {
@@ -664,7 +702,7 @@ std::string GCodeWriter::eager_lift(const LiftType type) {

    // BBS: spiral lift only safe with known position
    // TODO: check the arc will move within bed area
-    if (type == LiftType::SpiralLift && this->is_current_position_clear()) {
+    if (effective_type == LiftType::SpiralLift && this->is_current_position_clear()) {
        double radius = target_lift / (2 * PI * atan(filament()->travel_slope()));
        // static spiral alignment when no move in x,y plane.
        // spiral centra is a radius distance to the right (y=0) 
@@ -839,7 +877,13 @@ std::string GCodeWriter::_travel_to_z(double z, const std::string &comment)
    }

    GCodeG1Formatter w;
-    w.emit_z(z);
+    if (has_axis_remap()) {
+        // Remap may couple Z with other axes; emit full XYZ.
+        Vec3d machine = apply_axis_remap(Vec3d(m_pos.x() - m_x_offset, m_pos.y() - m_y_offset, z));
+        w.emit_xyz(machine);
+    } else {
+        w.emit_z(z);
+    }
    w.emit_f(speed * 60.0);
    //BBS
    w.emit_comment(GCodeWriter::full_gcode_comment, comment);
@@ -944,7 +988,12 @@ std::string GCodeWriter::extrude_to_xy(const Vec2d &point, double dE, const std:
    Vec2d point_on_plate = { point(0) - m_x_offset, point(1) - m_y_offset };

    GCodeG1Formatter w;
-    w.emit_xy(point_on_plate);
+    if (has_axis_remap()) {
+        Vec3d machine = apply_axis_remap(Vec3d(point_on_plate.x(), point_on_plate.y(), m_pos.z()));
+        w.emit_xyz(machine);
+    } else {
+        w.emit_xy(point_on_plate);
+    }
    if (!force_no_extrusion)
        w.emit_e(filament()->E());
    //BBS
@@ -989,6 +1038,9 @@ std::string GCodeWriter::extrude_to_xyz(const Vec3d &point, double dE, const std
    //BBS: take plate offset into consider
    Vec3d point_on_plate = { point(0) - m_x_offset, point(1) - m_y_offset, point(2) };

+    if (has_axis_remap())
+        point_on_plate = apply_axis_remap(point_on_plate);
+
    GCodeG1Formatter w;
    if (z_changed)
        w.emit_xyz(point_on_plate);
@@ -8,11 +8,11 @@
 #include "Point.hpp"
 #include "PrintConfig.hpp"
 #include "GCode/CoolingBuffer.hpp"
-
 namespace Slic3r {

 class GCodeWriter {
 public:
+    virtual ~GCodeWriter() = default;
    GCodeConfig config;
    bool multiple_extruders;

@@ -73,21 +73,21 @@ public:
    std::string set_speed(double F, const std::string &comment = std::string(), const std::string &cooling_marker = std::string());
    // SoftFever NOTE: the returned speed is mm/minute
    double      get_current_speed() const { return m_current_speed;}
-    std::string travel_to_xy(const Vec2d &point, const std::string &comment = std::string());
-    std::string travel_to_xyz(const Vec3d &point, const std::string &comment = std::string(), bool force_z = false);
+    virtual std::string travel_to_xy(const Vec2d &point, const std::string &comment = std::string());
+    virtual std::string travel_to_xyz(const Vec3d &point, const std::string &comment = std::string(), bool force_z = false);
    std::string travel_to_z(double z, const std::string &comment = std::string(), bool force = false);
    bool        will_move_z(double z) const;
-    std::string extrude_to_xy(const Vec2d &point, double dE, const std::string &comment = std::string(), bool force_no_extrusion = false);
+    virtual std::string extrude_to_xy(const Vec2d &point, double dE, const std::string &comment = std::string(), bool force_no_extrusion = false);
    //BBS: generate G2 or G3 extrude which moves by arc
    std::string extrude_arc_to_xy(const Vec2d &point, const Vec2d &center_offset, double dE, const bool is_ccw, const std::string &comment = std::string(), bool force_no_extrusion = false);
-    std::string extrude_to_xyz(const Vec3d &point, double dE, const std::string &comment = std::string(), bool force_no_extrusion = false);
+    virtual std::string extrude_to_xyz(const Vec3d &point, double dE, const std::string &comment = std::string(), bool force_no_extrusion = false);
    std::string retract(bool before_wipe = false, double retract_length = 0);
    std::string retract_for_toolchange(bool before_wipe = false, double retract_length = 0);
    std::string unretract();
    // do lift instantly
-    std::string eager_lift(const LiftType type);
+    virtual std::string eager_lift(const LiftType type);
    // record a lift request, do realy lift in next travel
-    std::string lazy_lift(LiftType lift_type = LiftType::NormalLift, bool spiral_vase = false);
+    virtual std::string lazy_lift(LiftType lift_type = LiftType::NormalLift, bool spiral_vase = false);
    std::string unlift();
    const Vec3d& get_position() const { return m_pos; }
    Vec3d&       get_position() { return m_pos; }
@@ -127,9 +127,38 @@ public:
    void set_is_first_layer(bool bval) { m_is_first_layer = bval; }
    GCodeFlavor get_gcode_flavor() const { return config.gcode_flavor; }

+    // Axis remap: permute/negate/reverse axes in G-code output.
+    // Works standalone (without belt mode) for printers with non-standard axis conventions.
+    void set_axis_remap(int rx, int ry, int rz);
+    void set_build_volume_max(const Vec3d &max);
+    bool has_axis_remap() const;
+
    // Returns whether this flavor supports separate print and travel acceleration.
    static bool supports_separate_travel_acceleration(GCodeFlavor flavor);
-  private:
+protected:
+    // Position/lift/offset state — accessible to subclasses (e.g. BeltGCodeWriter)
+    Vec3d           m_pos = Vec3d::Zero();
+    double          m_x_offset{ 0 };
+    double          m_y_offset{ 0 };
+    double          m_lifted;
+    double          m_to_lift;
+    LiftType        m_to_lift_type;
+    bool            m_is_first_layer = true;
+    bool            m_is_current_pos_clear = false;
+    double          m_current_speed;
+
+    virtual std::string _travel_to_z(double z, const std::string &comment);
+
+    // Axis remap state — accessible to subclasses.
+    int             m_remap_x = 0;  // RemapAxis: 0=+X, 1=+Y, 2=+Z, 3=-X, etc.
+    int             m_remap_y = 1;
+    int             m_remap_z = 2;
+    Vec3d           m_build_vol_max = Vec3d::Zero();
+
+    // Apply axis remap to a point. Returns pos unchanged if remap is identity.
+    Vec3d apply_axis_remap(const Vec3d &pos) const;
+
+private:
 	// Extruders are sorted by their ID, so that binary search is possible.
    std::vector<Extruder> m_filament_extruders;
    bool            m_single_extruder_multi_material;
@@ -157,37 +186,21 @@ public:
    unsigned int    m_last_additional_fan_speed;
    int             m_last_bed_temperature;
    bool            m_last_bed_temperature_reached;
-    double          m_lifted;
-
-    // BBS
-    double          m_to_lift;
-    LiftType        m_to_lift_type;
-    Vec3d           m_pos = Vec3d::Zero();
-    //BBS: this flag is used to indicate whether the m_pos is real.
-    //A example that of the first move, the m_pos is zero, but the real position of extruder doesn't
-    //Pos must be clear after the first xyz travel move
-    bool            m_is_current_pos_clear = false;
-    //BBS: x, y offset for gcode generated
-    double          m_x_offset{ 0 };
-    double          m_y_offset{ 0 };

    // Orca: slicing resolution in mm
    double          m_resolution = 0.01;
-    
+
    std::string m_gcode_label_objects_start;
    std::string m_gcode_label_objects_end;

    //SoftFever
    bool            m_is_bbl_printers = false;
-    double          m_current_speed;
-    bool            m_is_first_layer = true;

    enum class Acceleration {
        Travel,
        Print
    };

-    std::string _travel_to_z(double z, const std::string &comment);
    std::string _spiral_travel_to_z(double z, const Vec2d &ij_offset, const std::string &comment);
    std::string _retract(double length, double restart_extra, const std::string &comment);
    std::string set_acceleration_internal(Acceleration type, unsigned int acceleration);
@@ -1326,7 +1326,15 @@ static std::vector<std::string> s_Preset_machine_limits_options {

 static std::vector<std::string> s_Preset_printer_options {
    "printer_technology",
-    "printable_area", "extruder_printable_area", "support_parallel_printheads", "parallel_printheads_count", "parallel_printheads_bed_exclude_areas", "bed_exclude_area","bed_custom_texture", "bed_custom_model", "gcode_flavor",
+    "printable_area", "extruder_printable_area", "support_parallel_printheads", "parallel_printheads_count", "parallel_printheads_bed_exclude_areas", "bed_exclude_area","bed_custom_texture", "bed_custom_model", "build_plate_tilt_x", "build_plate_tilt_y", "belt_printer", "belt_printer_infinite_y",
+    "belt_slice_rotation", "belt_slice_rotation_angle", "belt_slice_rotation_global",
+    "preslice_remap_x", "preslice_remap_y", "preslice_remap_z", "preslice_remap_global",
+    "gcode_remap_x", "gcode_remap_y", "gcode_remap_z", "gcode_back_transform",
+    "belt_frame_tilt_decouple", "belt_frame_tilt_angle",
+    "belt_preslice_global",
+    "first_layer_plane", "first_layer_plane_offset", "first_layer_plane_thickness",
+    "belt_support_floor_offset", "belt_support_floor_mode", "belt_support_z_offset_mode",
+    "gcode_flavor",
    "fan_kickstart", "part_cooling_fan_min_pwm", "fan_speedup_time", "fan_speedup_overhangs",
    "single_extruder_multi_material", "manual_filament_change", "file_start_gcode", "machine_start_gcode", "machine_end_gcode", "before_layer_change_gcode", "printing_by_object_gcode", "layer_change_gcode", "time_lapse_gcode", "wrapping_detection_gcode", "change_filament_gcode", "change_extrusion_role_gcode",
    "printer_model", "printer_variant", "printer_extruder_id", "printer_extruder_variant", "extruder_variant_list", "default_nozzle_volume_type",
@@ -12,6 +12,7 @@
 #include "Thread.hpp"
 #include "Time.hpp"
 #include "GCode.hpp"
+#include "BeltGCode.hpp"
 #include "GCode/WipeTower.hpp"
 #include "GCode/WipeTower2.hpp"
 #include "Utils.hpp"
@@ -101,6 +102,12 @@ bool Print::invalidate_state_by_config_options(const ConfigOptionResolver & /* n
    // Cache the plenty of parameters, which influence the G-code generator only,
    // or they are only notes not influencing the generated G-code.
    static std::unordered_set<std::string> steps_gcode = {
+        // Belt printer G-code axis remap (only affects G-code output, not slicing).
+        "gcode_remap_x",
+        "gcode_remap_y",
+        "gcode_remap_z",
+        // Machine-frame transform (derived from belt tilt; only affects G-code output).
+        "belt_frame_tilt_decouple", "belt_frame_tilt_angle",
        //BBS
        "additional_cooling_fan_speed",
        "reduce_crossing_wall",
@@ -281,8 +288,26 @@ bool Print::invalidate_state_by_config_options(const ConfigOptionResolver & /* n
            // Spiral Vase forces different kind of slicing than the normal model:
            // In Spiral Vase mode, holes are closed and only the largest area contour is kept at each layer.
            // Therefore toggling the Spiral Vase on / off requires complete reslicing.
-            || opt_key == "spiral_mode") {
+            || opt_key == "spiral_mode"
+            // Build plate tilt changes slicing plane orientation.
+            || opt_key == "build_plate_tilt_x"
+            || opt_key == "build_plate_tilt_y"
+            // Belt printer transform options change the mesh geometry before slicing.
+            || opt_key == "belt_printer"
+            || opt_key == "belt_slice_rotation"
+            || opt_key == "belt_slice_rotation_angle"
+            || opt_key == "belt_slice_rotation_global"
+            || opt_key == "belt_preslice_global"
+            || opt_key == "preslice_remap_global"
+            || opt_key == "preslice_remap_x"
+            || opt_key == "preslice_remap_y"
+            || opt_key == "preslice_remap_z") {
            osteps.emplace_back(posSlice);
+        } else if (
+               opt_key == "belt_support_floor_offset"
+            || opt_key == "belt_support_floor_mode"
+            || opt_key == "belt_support_z_offset_mode") {
+            osteps.emplace_back(posSupportMaterial);
        } else if (
               opt_key == "print_sequence"
            || opt_key == "filament_type"
@@ -574,6 +599,9 @@ std::vector<ObjectID> Print::print_object_ids() const

 bool Print::has_infinite_skirt() const
 {
+    // Belt printer: no skirt support.
+    if (m_config.belt_printer.value)
+        return false;
    // Orca: unclear why (m_config.ooze_prevention && this->extruders().size() > 1) logic is here, removed.
    // return (m_config.draft_shield == dsEnabled && m_config.skirt_loops > 0) || (m_config.ooze_prevention && this->extruders().size() > 1);

@@ -582,6 +610,9 @@ bool Print::has_infinite_skirt() const

 bool Print::has_skirt() const
 {
+    // Belt printer: no skirt support.
+    if (m_config.belt_printer.value)
+        return false;
    return (m_config.skirt_height > 0);
 }

@@ -1283,6 +1314,16 @@ StringObjectException Print::validate(std::vector<StringObjectException> *warnin
    if (extruders.empty())
        return { L("No extrusions under current settings.") };

+    // Belt printer validation: incompatible features.
+    if (m_config.belt_printer.value) {
+        for (const PrintObject *object : m_objects) {
+            if (object->config().raft_layers > 0)
+                return { L("Raft is not compatible with belt printer mode.") };
+        }
+        if (m_config.draft_shield != dsDisabled)
+            return { L("Draft shield is not compatible with belt printer mode.") };
+    }
+
    if (nozzles < 2 && extruders.size() > 1) {
        auto ret = check_multi_filament_valid(*this);
        if (!ret.string.empty())
@@ -1374,6 +1415,28 @@ StringObjectException Print::validate(std::vector<StringObjectException> *warnin
    // Checks that the print does not exceed the max print height
    for (size_t print_object_idx = 0; print_object_idx < m_objects.size(); ++ print_object_idx) {
        const PrintObject &print_object = *m_objects[print_object_idx];
+        // Belt printer: the sliced (virtual) Z is belt travel along the conveyor, not
+        // build height, so the loop below (which measures the sliced layer stack) is
+        // meaningless here. The real ceiling is the usable vertical clearance above the
+        // belt, which printable_height holds directly: the gantry travels up the tilted
+        // plane, so a part of height z needs gantry reach z / cos(tilt), and the machine's
+        // gantry-axis range is sized to accommodate that (e.g. IdeaFormer IR3 V2: ~354 mm
+        // of gantry travel = 250 mm vertical at 45°, and printable_height = 250). So compare
+        // the upright object height against printable_height directly.
+        if (m_config.belt_printer.value) {
+            const double max_h = m_config.printable_height.value;
+            double obj_top = 0.0;
+            const ModelObject *mo = print_object.model_object();
+            for (const ModelInstance *mi : mo->instances)
+                obj_top = std::max(obj_top, mo->instance_bounding_box(*mi).max.z());
+            if (obj_top > max_h + EPSILON)
+                return StringObjectException{
+                    Slic3r::format(_u8L("The object %1% exceeds the maximum printable height "
+                        "above the belt (%2% mm)."),
+                        print_object.model_object()->name, max_h),
+                    print_object.model_object(), "" };
+            continue;
+        }
        //FIXME It is quite expensive to generate object layers just to get the print height!
        if (auto layers = generate_object_layers(print_object.slicing_parameters(), layer_height_profile(print_object_idx), print_object.config().precise_z_height.value);
            !layers.empty()) {
@@ -2247,15 +2310,24 @@ void Print::process(long long *time_cost_with_cache, bool use_cache)
    int object_count = m_objects.size();
    std::set<PrintObject*> need_slicing_objects;
    std::set<PrintObject*> re_slicing_objects;
+    // Belt global modes couple each object's bed position into its layer Z values,
+    // so sharing layers between "identical" objects is wrong.
+    bool belt_no_share = m_config.belt_printer.value &&
+        ((m_config.belt_slice_rotation_global.value
+              && m_config.belt_slice_rotation.value != BeltRotationAxis::None)
+         || m_config.preslice_remap_global.value
+         || m_config.belt_preslice_global.value);
    if (!use_cache) {
        for (int index = 0; index < object_count; index++)
        {
            PrintObject *obj =  m_objects[index];
-            for (PrintObject *slicing_obj : need_slicing_objects)
-            {
-                if (is_print_object_the_same(obj, slicing_obj)) {
-                    obj->set_shared_object(slicing_obj);
-                    break;
+            if (!belt_no_share) {
+                for (PrintObject *slicing_obj : need_slicing_objects)
+                {
+                    if (is_print_object_the_same(obj, slicing_obj)) {
+                        obj->set_shared_object(slicing_obj);
+                        break;
+                    }
                }
            }
            if (!obj->get_shared_object())
@@ -2274,12 +2346,14 @@ void Print::process(long long *time_cost_with_cache, bool use_cache)
            PrintObject *obj =  m_objects[index];
            bool found_shared = false;
            if (need_slicing_objects.find(obj) == need_slicing_objects.end()) {
-                for (PrintObject *slicing_obj : need_slicing_objects)
-                {
-                    if (is_print_object_the_same(obj, slicing_obj)) {
-                        obj->set_shared_object(slicing_obj);
-                        found_shared = true;
-                        break;
+                if (!belt_no_share) {
+                    for (PrintObject *slicing_obj : need_slicing_objects)
+                    {
+                        if (is_print_object_the_same(obj, slicing_obj)) {
+                            obj->set_shared_object(slicing_obj);
+                            found_shared = true;
+                            break;
+                        }
                    }
                }
                if (!found_shared) {
@@ -2641,12 +2715,17 @@ std::string Print::export_gcode(const std::string& path_template, GCodeProcessor
    this->set_status(80, message);

    // The following line may die for multiple reasons.
-    GCode gcode;
+    // Factory: use BeltGCode for belt printers, plain GCode otherwise.
+    std::unique_ptr<GCode> gcode;
+    if (m_config.belt_printer.value)
+        gcode = std::make_unique<BeltGCode>();
+    else
+        gcode = std::make_unique<GCode>();
    //BBS: compute plate offset for gcode-generator
    const Vec3d origin = this->get_plate_origin();
-    gcode.set_gcode_offset(origin(0), origin(1));
-    gcode.do_export(this, path.c_str(), result, thumbnail_cb);
-    gcode.export_layer_filaments(result);
+    gcode->set_gcode_offset(origin(0), origin(1));
+    gcode->do_export(this, path.c_str(), result, thumbnail_cb);
+    gcode->export_layer_filaments(result);
    //BBS
    if (result != nullptr)
        result->conflict_result = m_conflict_result;
@@ -2655,6 +2734,10 @@ std::string Print::export_gcode(const std::string& path_template, GCodeProcessor

 void Print::_make_skirt()
 {
+    // Belt printer: skirt is not compatible.
+    if (m_config.belt_printer.value)
+        return;
+  
    const bool generate_skirt = this->has_skirt() || this->has_infinite_skirt();

    // First off we need to decide how tall the skirt must be.
@@ -17,6 +17,7 @@
 #include "GCode/ThumbnailData.hpp"
 #include "GCode/GCodeProcessor.hpp"
 #include "MultiMaterialSegmentation.hpp"
+#include "BeltTransform.hpp"
 #include "libslic3r.h"

 #include <Eigen/Geometry>
@@ -186,6 +187,13 @@ class ConstSupportLayerPtrsAdaptor : public ConstVectorOfPtrsAdaptor<SupportLaye
    ConstSupportLayerPtrsAdaptor(const SupportLayerPtrs *data) : ConstVectorOfPtrsAdaptor<SupportLayer>(data) {}
 };

+// Returns the model's raw bounding box with pre-slice axis remap applied.
+// When no remap is active, returns the unmodified raw_bounding_box().
+inline BoundingBoxf3 belt_remapped_bbox(const ModelObject &model_object, const PrintConfig &config)
+{
+    return BeltTransformPipeline::remap_bbox(model_object, config);
+}
+
 // Single instance of a PrintObject.
 // As multiple PrintObjects may be generated for a single ModelObject (their instances differ in rotation around Z),
 // ModelObject's instancess will be distributed among these multiple PrintObjects.
@@ -575,7 +583,27 @@ private:

    PrintObject*                            m_shared_object{ nullptr };

-    
+    // Belt printer: global Z offset applied to this object's layers for shear positioning.
+    double                                  m_belt_global_z_offset { 0.0 };
+    // Belt printer: min_z of mesh after belt shear (before Z-shift), for z_offset calc.
+    double                                  m_belt_min_z { 0.0 };
+    // Belt printer: XY correction from global pre-slice mode, applied to G-code origin.
+    Vec2d                                   m_belt_global_xy_correction { Vec2d::Zero() };
+    // Belt printer: exact belt_floor_z_shift computed during posSlice from a
+    // vertex-level scan of the post-transform mesh.  Cached separately from
+    // m_slicing_params so that rebuilding m_slicing_params on a non-belt-affecting
+    // invalidation (e.g. support config change) doesn't replace the exact value
+    // with the bbox approximation seeded by create_from_config().  Cleared when
+    // posSlice is invalidated.
+    double                                  m_belt_floor_z_shift_cached { 0.0 };
+    bool                                    m_belt_floor_z_shift_cache_valid { false };
+public:
+    double belt_global_z_offset() const { return m_belt_global_z_offset; }
+    double belt_min_z() const { return m_belt_min_z; }
+    Vec2d  belt_global_xy_correction() const { return m_belt_global_xy_correction; }
+private:
+
+
    // SoftFever
    // 
    // object id
@@ -1,6 +1,7 @@
 #include "ClipperUtils.hpp"
 #include "Model.hpp"
 #include "Print.hpp"
+#include "BeltTransform.hpp"

 #include <boost/log/trivial.hpp>
 #include <cfloat>
@@ -135,22 +136,29 @@ struct PrintObjectTrafoAndInstances

 // Generate a list of trafos and XY offsets for instances of a ModelObject
 // Orca: Updated to include XYZ filament shrinkage compensation
-static std::vector<PrintObjectTrafoAndInstances> print_objects_from_model_object(const ModelObject &model_object, const Vec3d &shrinkage_compensation)
+static std::vector<PrintObjectTrafoAndInstances> print_objects_from_model_object(const ModelObject &model_object, const Vec3d &shrinkage_compensation, bool force_separate_instances = false)
 {
    std::set<PrintObjectTrafoAndInstances> trafos;
    PrintObjectTrafoAndInstances           trafo;
    //BBS: add useful logs for debug
    int index = 0;
+    int unique_counter = 0;
    for (ModelInstance *model_instance : model_object.instances) {
        if (model_instance->is_printable()) {
            // Orca: Updated with XYZ filament shrinkage compensation
            Geometry::Transformation model_instance_transformation = model_instance->get_transformation();
            trafo.trafo = model_instance_transformation.get_matrix_with_applied_shrinkage_compensation(shrinkage_compensation);
-            
+
            auto shift = Point::new_scale(trafo.trafo.data()[12], trafo.trafo.data()[13]);
            // Reset the XY axes of the transformation.
            trafo.trafo.data()[12] = 0;
            trafo.trafo.data()[13] = 0;
+            // Belt printer global mode: prevent instance grouping so each
+            // copy gets its own PrintObject with independent layer Z values.
+            // Add a tiny unique perturbation to the existing Z (don't replace
+            // it — the Z translation from ensure_on_bed must be preserved).
+            if (force_separate_instances)
+                trafo.trafo.data()[14] += 1e-10 * (++unique_counter);
            // Search or insert a trafo.
            auto it = trafos.emplace(trafo).first;
            const_cast<PrintObjectTrafoAndInstances&>(*it).instances.emplace_back(PrintInstance{ nullptr, model_instance, shift });
@@ -1527,11 +1535,20 @@ Print::ApplyStatus Print::apply(const Model &model, DynamicPrintConfig new_full_
        PrintObjectPtrs print_objects_new;
        print_objects_new.reserve(std::max(m_objects.size(), m_model.objects.size()));
        bool new_objects = false;
+        bool belt_instances_shifted = false;
        // Walk over all new model objects and check, whether there are matching PrintObjects.
        for (ModelObject *model_object : m_model.objects) {
            ModelObjectStatus &model_object_status = const_cast<ModelObjectStatus&>(model_object_status_db.reuse(*model_object));
            // Orca: Updated for XYZ filament shrink compensation
-            model_object_status.print_instances = print_objects_from_model_object(*model_object, this->shrinkage_compensation());
+            // Belt global mode: force each instance into its own PrintObject
+            // so each gets independent layer Z values.
+            bool belt_force_separate = m_config.belt_printer.value && (
+                (m_config.belt_slice_rotation_global.value
+                    && m_config.belt_slice_rotation.value != BeltRotationAxis::None
+                    && std::abs(m_config.belt_slice_rotation_angle.value) > EPSILON)
+                || m_config.belt_preslice_global.value
+                || (m_config.preslice_remap_global.value && BeltTransformPipeline::has_preslice_remap(m_config)));
+            model_object_status.print_instances = print_objects_from_model_object(*model_object, this->shrinkage_compensation(), belt_force_separate);
            std::vector<const PrintObjectStatus*> old;
            old.reserve(print_object_status_db.count(*model_object));
            for (const PrintObjectStatus &print_object_status : print_object_status_db.get_range(*model_object))
@@ -1579,6 +1596,7 @@ Print::ApplyStatus Print::apply(const Model &model, DynamicPrintConfig new_full_
                    if (status != PrintBase::APPLY_STATUS_UNCHANGED) {
                        size_t extruder_num = new_full_config.option<ConfigOptionFloats>("nozzle_diameter")->size();
                        update_apply_status(status == PrintBase::APPLY_STATUS_INVALIDATED);
+                        belt_instances_shifted = true;
                    }
 					print_objects_new.emplace_back((*it_old)->print_object);
 					const_cast<PrintObjectStatus*>(*it_old)->status = PrintObjectStatus::Reused;
@@ -1614,6 +1632,20 @@ Print::ApplyStatus Print::apply(const Model &model, DynamicPrintConfig new_full_
                update_apply_status(object->invalidate_step(posSlice));
            }
        }
+
+        // Belt printer global mode: when any object's instances shifted,
+        // recompute m_belt_global_z_offset for ALL objects (it depends on
+        // min_shift across all objects, so one move affects everyone).
+        if (belt_instances_shifted
+            && m_config.belt_printer.value
+            && ((m_config.belt_slice_rotation_global.value
+                    && m_config.belt_slice_rotation.value != BeltRotationAxis::None
+                    && std::abs(m_config.belt_slice_rotation_angle.value) > EPSILON)
+                || m_config.belt_preslice_global.value
+                || (m_config.preslice_remap_global.value && BeltTransformPipeline::has_preslice_remap(m_config)))) {
+            for (PrintObject *object : m_objects)
+                update_apply_status(object->invalidate_step(posSlice));
+        }
    }

    //BBS: check the config again
@@ -1,7 +1,9 @@
 #include "PrintConfig.hpp"
 #include "PrintConfigConstants.hpp"
+#include "BeltTransform.hpp"
 #include "ClipperUtils.hpp"
 #include "Config.hpp"
+#include "Geometry.hpp"
 #include "MaterialType.hpp"
 #include "I18N.hpp"
 #include "format.hpp"
@@ -308,6 +310,54 @@ static t_config_enum_values s_keys_map_SlicingMode {
 };
 CONFIG_OPTION_ENUM_DEFINE_STATIC_MAPS(SlicingMode)

+static t_config_enum_values s_keys_map_BeltRotationAxis {
+    { "none", int(BeltRotationAxis::None) },
+    { "x",    int(BeltRotationAxis::X) },
+    { "y",    int(BeltRotationAxis::Y) },
+    { "z",    int(BeltRotationAxis::Z) },
+};
+CONFIG_OPTION_ENUM_DEFINE_STATIC_MAPS(BeltRotationAxis)
+
+static t_config_enum_values s_keys_map_RemapAxis {
+    { "pos_x", int(RemapAxis::PosX) },
+    { "pos_y", int(RemapAxis::PosY) },
+    { "pos_z", int(RemapAxis::PosZ) },
+    { "neg_x", int(RemapAxis::NegX) },
+    { "neg_y", int(RemapAxis::NegY) },
+    { "neg_z", int(RemapAxis::NegZ) },
+    { "rev_x", int(RemapAxis::RevX) },
+    { "rev_y", int(RemapAxis::RevY) },
+    { "rev_z", int(RemapAxis::RevZ) },
+};
+CONFIG_OPTION_ENUM_DEFINE_STATIC_MAPS(RemapAxis)
+
+static t_config_enum_values s_keys_map_BeltSupportFloorMode {
+    { "none",           int(BeltSupportFloorMode::None) },
+    { "generator_only", int(BeltSupportFloorMode::GeneratorOnly) },
+    { "clip_only",      int(BeltSupportFloorMode::ClipOnly) },
+    { "both",           int(BeltSupportFloorMode::Both) },
+};
+CONFIG_OPTION_ENUM_DEFINE_STATIC_MAPS(BeltSupportFloorMode)
+
+static t_config_enum_values s_keys_map_BeltSupportZOffsetMode {
+    { "none",           int(BeltSupportZOffsetMode::None) },
+    { "unconditional",  int(BeltSupportZOffsetMode::Unconditional) },
+    { "raft_only",      int(BeltSupportZOffsetMode::RaftOnly) },
+};
+CONFIG_OPTION_ENUM_DEFINE_STATIC_MAPS(BeltSupportZOffsetMode)
+
+static t_config_enum_values s_keys_map_FirstLayerPlaneMode {
+    { "auto",        int(FirstLayerPlaneMode::Auto) },
+    { "xy",          int(FirstLayerPlaneMode::XY) },
+    { "yz",          int(FirstLayerPlaneMode::YZ) },
+    { "xz",          int(FirstLayerPlaneMode::XZ) },
+    { "belt_affine", int(FirstLayerPlaneMode::BeltAffine) },
+    // Back-compat alias: pre-rotation builds serialised this mode as
+    // "belt_shear".  Accept it on parse so old 3MFs / presets keep loading.
+    { "belt_shear",  int(FirstLayerPlaneMode::BeltAffine) },
+};
+CONFIG_OPTION_ENUM_DEFINE_STATIC_MAPS(FirstLayerPlaneMode)
+
 static t_config_enum_values s_keys_map_SupportMaterialPattern {
    { "rectilinear",        smpRectilinear },
    { "rectilinear-grid",   smpRectilinearGrid },
@@ -6343,6 +6393,266 @@ void PrintConfigDef::init_fff_params()
    def->mode = comSimple;
    def->set_default_value(new ConfigOptionFloatOrPercent(50., true));

+    def = this->add("build_plate_tilt_x", coFloat);
+    def->label = L("Build plate tilt X");
+    def->category = L("Support");
+    def->tooltip = L("Tilt angle of the build plate along the X axis. "
+                     "A positive value tilts the plate so the +X side is higher, shifting gravity toward -X and increasing overhangs on the +X side. "
+                     "A negative value tilts the -X side higher. Set to 0 for no X-axis tilt. "
+                     "In belt printer mode, this is automatically synced to the belt angle.");
+    def->sidetext = u8"\u00B0";
+    def->min = -90;
+    def->max = 90;
+    def->mode = comExpert;
+    def->set_default_value(new ConfigOptionFloat(0.));
+
+    def = this->add("build_plate_tilt_y", coFloat);
+    def->label = L("Build plate tilt Y");
+    def->category = L("Support");
+    def->tooltip = L("Tilt angle of the build plate along the Y axis. "
+                     "A positive value tilts the plate so the +Y side is higher, shifting gravity toward -Y and increasing overhangs on the +Y side. "
+                     "A negative value tilts the -Y side higher. Set to 0 for no Y-axis tilt.");
+    def->sidetext = u8"\u00B0";
+    def->min = -90;
+    def->max = 90;
+    def->mode = comExpert;
+    def->set_default_value(new ConfigOptionFloat(0.));
+
+    def = this->add("belt_printer", coBool);
+    def->label = L("Enable belt printing");
+    def->category = L("Printable space");
+    def->tooltip = L("Enable belt printer mode. Belt printers use a conveyor belt as the build surface, "
+                     "tilted at an angle (typically 45 degrees). The slicer will rotate the slicing plane "
+                     "and transform G-code coordinates for the tilted build surface.");
+    def->mode = comAdvanced;
+    def->set_default_value(new ConfigOptionBool(false));
+
+    def = this->add("belt_printer_infinite_y", coBool);
+    def->label = L("Infinite Y axis");
+    def->category = L("Printable space");
+    def->tooltip = L("Enable infinite Y axis for belt printers. "
+                     "When enabled, the Y axis build volume limit is effectively removed, "
+                     "allowing objects of any length to be printed along the belt direction.");
+    def->mode = comAdvanced;
+    def->set_default_value(new ConfigOptionBool(true));
+
+    // Mesh rotation applied before slicing — the sole mesh-side belt transform AND
+    // the single source of truth for the physical belt tilt (bed rendering, support
+    // gravity tilt and bed-exclusion projection all derive their angle from this).
+    def = this->add("belt_slice_rotation", coEnum);
+    def->label = L("Belt tilt axis");
+    def->category = L("Printable space");
+    def->tooltip = L("Axis the mesh is rotated about before slicing. This is the belt "
+                     "printer's tilt: an isometric (no distortion) rotation that also "
+                     "drives bed rendering and support gravity tilt, and that the g-code "
+                     "back-transform inverts before the machine-frame shear/scale and remap. "
+                     "X is the typical gantry tilt (belt travels along Y).");
+    def->enum_keys_map = &ConfigOptionEnum<BeltRotationAxis>::get_enum_values();
+    def->enum_values  = {"none", "x", "y", "z"};
+    def->enum_labels  = {L("None"), L("X"), L("Y"), L("Z")};
+    def->mode = comAdvanced;
+    def->set_default_value(new ConfigOptionEnum<BeltRotationAxis>(BeltRotationAxis::X));
+
+    def = this->add("belt_slice_rotation_angle", coFloat);
+    def->label = L("Belt tilt angle");
+    def->category = L("Printable space");
+    def->tooltip = L("Tilt angle of the belt surface, in degrees. Most belt printers use "
+                     "45°. Positive values rotate counter-clockwise looking down the "
+                     "positive tilt axis; the magnitude is also the physical belt tilt "
+                     "used for bed rendering and support gravity.");
+    def->sidetext = L("°");
+    def->min = -180.;
+    def->max = 180.;
+    def->mode = comAdvanced;
+    def->set_default_value(new ConfigOptionFloat(45.));
+
+    def = this->add("belt_slice_rotation_global", coBool);
+    def->label = L("Global");
+    def->category = L("Printable space");
+    def->tooltip = L("Treat the slicing rotation as part of the global forward transform "
+                     "that BeltBackTransform inverts before the machine-frame remap. "
+                     "Required for rotation-mode belt printers. "
+                     "Defaults to on because virtually all rotation-mode printers need it.");
+    def->mode = comAdvanced;
+    def->set_default_value(new ConfigOptionBool(true));
+
+    def = this->add("belt_frame_tilt_decouple", coBool);
+    def->label = L("Decouple machine-frame tilt");
+    def->category = L("Printable space");
+    def->tooltip = L("Expert override: set the machine-frame (g-code shear/scale) tilt angle "
+                     "independently of the pre-slice rotation angle. When disabled, the "
+                     "machine-frame transform is derived from the belt tilt angle, so a single "
+                     "angle drives both stages. Enable only to compensate for a machine whose "
+                     "physical gantry tilt differs from the slicing rotation.");
+    def->mode = comExpert;
+    def->set_default_value(new ConfigOptionBool(false));
+
+    def = this->add("belt_frame_tilt_angle", coFloat);
+    def->label = L("Machine-frame tilt angle");
+    def->category = L("Printable space");
+    def->tooltip = L("Tilt angle (degrees) used to derive the machine-frame shear (tan) and "
+                     "scale (1/cos) applied to G-code. Only used when 'Decouple machine-frame "
+                     "tilt' is enabled; otherwise the belt tilt angle is used.");
+    def->sidetext = L("°");
+    def->min = -89.9;
+    def->max = 89.9;
+    def->mode = comExpert;
+    def->set_default_value(new ConfigOptionFloat(45.));
+
+    // G-code axis remap with sign
+    auto add_belt_remap = [this](const char *key, const char *label, const char *tooltip,
+                                  RemapAxis default_axis, ConfigOptionMode mode = comSimple) {
+        auto def = this->add(key, coEnum);
+        def->label = L(label);
+        def->category = L("Printable space");
+        def->tooltip = L(tooltip);
+        def->enum_keys_map = &ConfigOptionEnum<RemapAxis>::get_enum_values();
+        def->enum_values  = {"pos_x", "pos_y", "pos_z", "neg_x", "neg_y", "neg_z", "rev_x", "rev_y", "rev_z"};
+        def->enum_labels  = {L("+X"), L("+Y"), L("+Z"), L("-X"), L("-Y"), L("-Z"), L("Rev X"), L("Rev Y"), L("Rev Z")};
+        def->mode = mode;  // Visibility may also be gated by toggle_line in Tab.cpp
+        def->set_default_value(new ConfigOptionEnum<RemapAxis>(default_axis));
+    };
+
+    add_belt_remap("preslice_remap_x", "X",
+        "Before slicing, which model-space axis becomes the slicer's X axis. "
+        "Use this to re-orient the coordinate system so the slicer's XY plane matches "
+        "your belt printer's physical bed plane. For a printer whose bed is in the XZ plane, "
+        "set Y to +Z and Z to +Y (or -Y) to swap the vertical and belt-travel axes. "
+        "Default +X: no change.",
+        RemapAxis::PosX, comExpert);
+    add_belt_remap("preslice_remap_y", "Y",
+        "Before slicing, which model-space axis becomes the slicer's Y axis. "
+        "The slicer treats Y as one of the two horizontal bed axes. If your physical "
+        "belt surface runs along the Z axis, map Y to +Z here so the slicer slices "
+        "along the correct plane. Default +Y: no change.",
+        RemapAxis::PosY, comExpert);
+    add_belt_remap("preslice_remap_z", "Z",
+        "Before slicing, which model-space axis becomes the slicer's Z axis (layer stacking direction). "
+        "The slicer builds layers upward along this axis. If your printer's layer-stacking "
+        "direction is the physical Y axis, map Z to +Y (or -Y for inverted direction). "
+        "Rev mode mirrors relative to the build volume maximum. Default +Z: no change.",
+        RemapAxis::PosZ, comExpert);
+
+    def = this->add("preslice_remap_global", coBool);
+    def->label = L("Global");
+    def->category = L("Printable space");
+    def->tooltip = L("When enabled, the pre-slice axis remap accounts for each object's bed position. "
+                      "Without this, the remap is applied locally around each object's center, so "
+                      "objects at different positions don't get a position-dependent contribution. "
+                      "Mirrors the 'Global' option on the belt slicing rotation, but for the remap.");
+    def->mode = comExpert;
+    def->set_default_value(new ConfigOptionBool(false));
+
+    add_belt_remap("gcode_remap_x", "X", "Which slicing axis maps to machine X in G-code output. Applied AFTER slicing, during G-code generation.", RemapAxis::PosX, comExpert);
+    add_belt_remap("gcode_remap_y", "Y", "Which slicing axis maps to machine Y in G-code output. Applied AFTER slicing, during G-code generation.", RemapAxis::PosY, comExpert);
+    add_belt_remap("gcode_remap_z", "Z", "Which slicing axis maps to machine Z in G-code output. Applied AFTER slicing, during G-code generation.", RemapAxis::PosZ, comExpert);
+
+    // The machine-frame G-code transform (shear + scale) is no longer configured
+    // by per-axis keys: it is derived from the belt tilt (belt_slice_rotation axis
+    // + angle, or belt_frame_tilt_angle when decoupled) in MachineFrameTransform.
+
+    def = this->add("gcode_back_transform", coBool);
+    def->label = L("G-code back-transform");
+    def->category = L("Printable space");
+    def->tooltip = L("Reverse the shear/scale transform applied during slicing so G-code "
+                      "coordinates are in the machine's physical coordinate space. "
+                      "Requires at least one shear axis with global mode enabled.");
+    def->mode = comExpert;
+    def->set_default_value(new ConfigOptionBool(true));
+
+    def = this->add("belt_preslice_global", coBool);
+    def->label = L("Global mesh transforms");
+    def->category = L("Printable space");
+    def->tooltip = L("When enabled, pre-slice belt transforms (remap, shear, scale) account for "
+                      "each object's bed position, producing correct machine coordinates without "
+                      "relying on origin snap. Each instance gets its own PrintObject.");
+    def->mode = comExpert;
+    def->set_default_value(new ConfigOptionBool(true));
+
+    // First-layer plane: which surface defines "first layer" for fan / speed /
+    // accel decisions.  On belt printers the slicing-frame layer 0 is a tilted
+    // slab that no longer corresponds to the physical first printed layer.
+    // Auto picks BeltAffine when any belt-side affine transform is active
+    // (Z shear or slicing rotation), otherwise XY (legacy).
+    def = this->add("first_layer_plane", coEnum);
+    def->label = L("First layer plane");
+    def->category = L("Printable space");
+    def->tooltip = L("Selects the reference plane used to decide which extrusions get "
+                     "first-layer settings (no fan, slow speed, initial-layer accel/jerk, "
+                     "deferred temperature drop). On belt printers a single slicing layer "
+                     "contains paths at many machine-Z values, so layer-index based detection "
+                     "fails. Auto resolves to Belt affine plane when any belt-side affine "
+                     "transform (Z shear or slicing rotation) is active, otherwise XY (legacy). "
+                     "Pick XY explicitly to opt out and force the legacy slicing-layer-0 "
+                     "detection.");
+    def->enum_keys_map = &ConfigOptionEnum<FirstLayerPlaneMode>::get_enum_values();
+    def->enum_values   = {"auto", "xy", "yz", "xz", "belt_affine"};
+    def->enum_labels   = {L("Auto"), L("XY (machine bed)"), L("YZ"), L("XZ"), L("Belt affine plane")};
+    def->mode = comExpert;
+    def->set_default_value(new ConfigOptionEnum<FirstLayerPlaneMode>(FirstLayerPlaneMode::BeltAffine));
+
+    def = this->add("first_layer_plane_offset", coFloat);
+    def->label = L("Belt plane offset");
+    def->category = L("Printable space");
+    def->tooltip = L("Shifts the first-layer plane along its normal (mm). For axis-aligned "
+                     "planes this is just a coordinate shift. Positive values move the plane "
+                     "away from the belt surface (deeper into the model).");
+    def->sidetext = L("mm");
+    def->min = -1000;
+    def->max =  1000;
+    def->mode = comAdvanced;
+    def->set_default_value(new ConfigOptionFloat(0.0));
+
+    def = this->add("first_layer_plane_thickness", coFloat);
+    def->label = L("Plane band thickness");
+    def->category = L("Printable space");
+    def->tooltip = L("Thickness of one 'band' relative to the first-layer plane, in mm. "
+                     "Used as the unit by which 'No cooling for the first N layers' (and "
+                     "similar layer-count thresholds) is multiplied when the first-layer "
+                     "plane is active. -1 means use initial_layer_print_height.");
+    def->sidetext = L("mm");
+    def->min = -1;
+    def->max = 100;
+    def->mode = comAdvanced;
+    def->set_default_value(new ConfigOptionFloat(-1.0));
+
+    // Belt support floor debug controls
+    def = this->add("belt_support_floor_offset", coFloat);
+    def->label = L("Support Floor Z offset");
+    def->category = L("Printable space");
+    def->tooltip = L("Shifts the computed belt floor up or down (mm). Negative values lower the floor, allowing more supports to survive. Use this to diagnose belt floor formula issues.");
+    def->sidetext = L("mm");
+    def->min = -500;
+    def->max = 500;
+    def->mode = comAdvanced;
+    def->set_default_value(new ConfigOptionFloat(0));
+
+    {
+        auto def = this->add("belt_support_floor_mode", coEnum);
+        def->label = L("Floor mode");
+        def->category = L("Printable space");
+        def->tooltip = L("Controls belt floor awareness for supports. 'None' disables belt floor logic. "
+                         "'Generator only' stops support generation at the belt floor plane.");
+        def->enum_keys_map = &ConfigOptionEnum<BeltSupportFloorMode>::get_enum_values();
+        def->enum_values  = {"none", "generator_only"};
+        def->enum_labels  = {L("None"), L("Generator only")};
+        def->mode = comDevelop;
+        def->set_default_value(new ConfigOptionEnum<BeltSupportFloorMode>(BeltSupportFloorMode::GeneratorOnly));
+    }
+
+    {
+        auto def = this->add("belt_support_z_offset_mode", coEnum);
+        def->label = L("Z offset mode");
+        def->category = L("Printable space");
+        def->tooltip = L("How global Z offset is applied to support layers for belt printers with global shear. "
+                         "'None' = don't offset. 'Unconditional' = offset all layers. 'Raft only' = only offset raft layers.");
+        def->enum_keys_map = &ConfigOptionEnum<BeltSupportZOffsetMode>::get_enum_values();
+        def->enum_values  = {"none", "unconditional", "raft_only"};
+        def->enum_labels  = {L("None"), L("Unconditional"), L("Raft only")};
+        def->mode = comExpert;
+        def->set_default_value(new ConfigOptionEnum<BeltSupportZOffsetMode>(BeltSupportZOffsetMode::Unconditional));
+    }
+
    def = this->add("tree_support_branch_angle", coFloat);
    def->label = L("Tree support branch angle");
    def->category = L("Support");
@@ -11432,10 +11742,22 @@ Polygons get_bed_excluded_area(const PrintConfig& cfg)
 {
    const Pointfs exclude_area_points = cfg.bed_exclude_area.values;

+    // Belt printer: project exclusion zone points from the belt surface to machine-frame XY.
+    // On the belt surface Z=0, so the in-plane axis foreshortens by cos(tilt).  The tilt
+    // axis decides which bed axis foreshortens: tilt about X (belt along Y) scales Y,
+    // tilt about Y (belt along X) scales X.  Derived from belt_slice_rotation.
+    const bool is_belt = cfg.belt_printer.value;
+    const auto tilt    = BeltTransformPipeline::physical_tilt(
+        cfg.belt_slice_rotation.value, cfg.belt_slice_rotation_angle.value);
+    const double cos_x = is_belt ? std::cos(Geometry::deg2rad(tilt.tilt_x_deg)) : 1.0; // foreshortens Y
+    const double cos_y = is_belt ? std::cos(Geometry::deg2rad(tilt.tilt_y_deg)) : 1.0; // foreshortens X
+
    Polygon exclude_poly;
    for (int i = 0; i < exclude_area_points.size(); i++) {
        auto pt = exclude_area_points[i];
-        exclude_poly.points.emplace_back(scale_(pt.x()), scale_(pt.y()));
+        double x = is_belt ? pt.x() * cos_y : pt.x();
+        double y = is_belt ? pt.y() * cos_x : pt.y();
+        exclude_poly.points.emplace_back(scale_(x), scale_(y));
    }

    exclude_poly.make_counter_clockwise();
@@ -169,6 +169,61 @@ enum class SlicingMode
    CloseHoles,
 };

+// Axis around which the mesh is rotated before slicing, when
+// `belt_slice_rotation` is set.  None disables the rotation stage.  This is the
+// single "belt tilt" axis: it drives both the pre-slice mesh rotation and the
+// post-slice machine-frame transform (shear + scale derived from the tilt angle).
+enum class BeltRotationAxis
+{
+    None = 0,
+    X    = 1,
+    Y    = 2,
+    Z    = 3,
+};
+
+enum class RemapAxis
+{
+    PosX = 0, PosY = 1, PosZ = 2,
+    NegX = 3, NegY = 4, NegZ = 5,
+    RevX = 6, RevY = 7, RevZ = 8,  // Reversed: max - pos
+};
+
+enum class BeltSupportFloorMode
+{
+    None,           // No belt floor awareness
+    GeneratorOnly,  // Only in tree support drop_nodes/contact_points
+    ClipOnly,       // Only post-processing clipping
+    Both,           // Both generator and clipping
+};
+
+enum class BeltSupportZOffsetMode
+{
+    None,           // Don't apply global_z_offset to support layers
+    Unconditional,  // Apply to all support layers
+    RaftOnly,       // Only apply to raft layers
+};
+
+// Selects which plane the slicer treats as the "first layer plane" — the
+// reference surface used to decide which extrusions get first-layer settings
+// (no fan, slow speed, initial-layer accel/jerk, deferred temperature drop).
+//
+// Auto resolves to:
+//   - XY (inactive, legacy behavior) for non-belt printers and for belt
+//     printers with no active belt-side transform.
+//   - BeltAffine for belt printers with any active belt-side affine
+//     transform (Z shear, slicing rotation, or both).
+//
+// XY is also used as an explicit "opt out" mode that forces legacy
+// per-layer first-layer detection even on belt printers.
+enum class FirstLayerPlaneMode
+{
+    Auto = 0,
+    XY,
+    YZ,
+    XZ,
+    BeltAffine,   // formerly BeltShear; renamed to reflect rotation support
+};
+
 enum SupportMaterialPattern {
    smpDefault,
    smpRectilinear, smpRectilinearGrid, smpHoneycomb,
@@ -528,6 +583,11 @@ CONFIG_OPTION_ENUM_DECLARE_STATIC_MAPS(NoiseType)
 CONFIG_OPTION_ENUM_DECLARE_STATIC_MAPS(InfillPattern)
 CONFIG_OPTION_ENUM_DECLARE_STATIC_MAPS(IroningType)
 CONFIG_OPTION_ENUM_DECLARE_STATIC_MAPS(SlicingMode)
+CONFIG_OPTION_ENUM_DECLARE_STATIC_MAPS(BeltRotationAxis)
+CONFIG_OPTION_ENUM_DECLARE_STATIC_MAPS(RemapAxis)
+CONFIG_OPTION_ENUM_DECLARE_STATIC_MAPS(BeltSupportFloorMode)
+CONFIG_OPTION_ENUM_DECLARE_STATIC_MAPS(BeltSupportZOffsetMode)
+CONFIG_OPTION_ENUM_DECLARE_STATIC_MAPS(FirstLayerPlaneMode)
 CONFIG_OPTION_ENUM_DECLARE_STATIC_MAPS(SupportMaterialPattern)
 CONFIG_OPTION_ENUM_DECLARE_STATIC_MAPS(SupportMaterialStyle)
 CONFIG_OPTION_ENUM_DECLARE_STATIC_MAPS(SupportMaterialInterfacePattern)
@@ -1480,6 +1540,40 @@ PRINT_CONFIG_CLASS_DERIVED_DEFINE(
    PrintConfig,
    (MachineEnvelopeConfig, GCodeConfig),

+    // Build plate tilt for off-axis gravity support generation (printer-level setting).
+    ((ConfigOptionFloat,               build_plate_tilt_x))
+    ((ConfigOptionFloat,               build_plate_tilt_y))
+    // Belt printer settings (printer-level).
+    ((ConfigOptionBool,                belt_printer))
+    ((ConfigOptionBool,                belt_printer_infinite_y))
+    // Mesh rotation applied before slicing — the single source of truth for the
+    // physical belt tilt.  Its angle + axis drive bed rendering, support gravity
+    // tilt, the bed-exclusion projection, AND the post-slice machine-frame
+    // transform (shear + scale, derived from the tilt angle; see
+    // MachineFrameTransform).  Isometric (no distortion) on the mesh side; the
+    // g-code back-transform inverts the rotation before the machine-frame stage.
+    ((ConfigOptionEnum<BeltRotationAxis>, belt_slice_rotation))
+    ((ConfigOptionFloat,                  belt_slice_rotation_angle))
+    ((ConfigOptionBool,                   belt_slice_rotation_global))
+    // Expert override: decouple the machine-frame tilt angle from the pre-slice
+    // rotation angle.  When disabled, the machine frame uses belt_slice_rotation_angle.
+    ((ConfigOptionBool,                   belt_frame_tilt_decouple))
+    ((ConfigOptionFloat,                  belt_frame_tilt_angle))
+    ((ConfigOptionEnum<RemapAxis>,  preslice_remap_x))
+    ((ConfigOptionEnum<RemapAxis>,  preslice_remap_y))
+    ((ConfigOptionEnum<RemapAxis>,  preslice_remap_z))
+    ((ConfigOptionBool,             preslice_remap_global))
+    ((ConfigOptionEnum<RemapAxis>,  gcode_remap_x))
+    ((ConfigOptionEnum<RemapAxis>,  gcode_remap_y))
+    ((ConfigOptionEnum<RemapAxis>,  gcode_remap_z))
+    ((ConfigOptionBool,                 gcode_back_transform))
+    ((ConfigOptionBool,                 belt_preslice_global))
+    ((ConfigOptionEnum<FirstLayerPlaneMode>, first_layer_plane))
+    ((ConfigOptionFloat,                first_layer_plane_offset))
+    ((ConfigOptionFloat,                first_layer_plane_thickness))
+    ((ConfigOptionFloat,                          belt_support_floor_offset))
+    ((ConfigOptionEnum<BeltSupportFloorMode>,     belt_support_floor_mode))
+    ((ConfigOptionEnum<BeltSupportZOffsetMode>,   belt_support_z_offset_mode))
    //BBS
    ((ConfigOptionInts,               additional_cooling_fan_speed))
    ((ConfigOptionInts,               close_additional_fan_first_x_layers))
@@ -2,6 +2,9 @@
 #include "Model.hpp"
 #include "Point.hpp"
 #include "Print.hpp"
+#include "BeltTransform.hpp"
+
+#include <thread>
 #include "BoundingBox.hpp"
 #include "ClipperUtils.hpp"
 #include "ElephantFootCompensation.hpp"
@@ -12,6 +15,7 @@
 #include "PrintConfig.hpp"
 #include "SLA/IndexedMesh.hpp"
 #include "Support/SupportMaterial.hpp"
+#include "Support/SupportCommon.hpp"
 #include "Support/SupportSpotsGenerator.hpp"
 #include "Support/TreeSupport.hpp"
 #include "Surface.hpp"
@@ -452,11 +456,15 @@ std::vector<std::set<int>> PrintObject::detect_extruder_geometric_unprintables()
 // 3) Generates perimeters, gap fills and fill regions (fill regions of type stInternal).
 void PrintObject::make_perimeters()
 {
+    BOOST_LOG_TRIVIAL(trace) << "[BELTRACE] make_perimeters request tid=" << std::this_thread::get_id() << " obj=" << this;
    // prerequisites
    this->slice();

-    if (! this->set_started(posPerimeters))
+    if (! this->set_started(posPerimeters)) {
+        BOOST_LOG_TRIVIAL(trace) << "[BELTRACE] make_perimeters SKIP tid=" << std::this_thread::get_id() << " obj=" << this << " (already started/done)";
        return;
+    }
+    BOOST_LOG_TRIVIAL(trace) << "[BELTRACE] make_perimeters ENTER tid=" << std::this_thread::get_id() << " obj=" << this;

    m_print->set_status(15, L("Generating walls"));
    BOOST_LOG_TRIVIAL(info) << "Generating walls..." << log_memory_info();
@@ -554,6 +562,7 @@ void PrintObject::make_perimeters()
    m_print->throw_if_canceled();
    BOOST_LOG_TRIVIAL(debug) << "Generating perimeters in parallel - end";

+    BOOST_LOG_TRIVIAL(trace) << "[BELTRACE] make_perimeters EXIT tid=" << std::this_thread::get_id() << " obj=" << this;
    this->set_done(posPerimeters);
 }

@@ -849,7 +858,9 @@ void PrintObject::detect_overhangs_for_lift()

 void PrintObject::generate_support_material()
 {
+    BOOST_LOG_TRIVIAL(trace) << "[BELTRACE] generate_support_material request tid=" << std::this_thread::get_id() << " obj=" << this;
    if (this->set_started(posSupportMaterial)) {
+        BOOST_LOG_TRIVIAL(trace) << "[BELTRACE] generate_support_material ENTER tid=" << std::this_thread::get_id() << " obj=" << this;
        this->clear_support_layers();

        if(!has_support() && !m_print->get_no_check_flag()) {
@@ -890,7 +901,10 @@ void PrintObject::generate_support_material()
            this->_generate_support_material();
            m_print->throw_if_canceled();
        }
+        BOOST_LOG_TRIVIAL(trace) << "[BELTRACE] generate_support_material EXIT tid=" << std::this_thread::get_id() << " obj=" << this;
        this->set_done(posSupportMaterial);
+    } else {
+        BOOST_LOG_TRIVIAL(trace) << "[BELTRACE] generate_support_material SKIP tid=" << std::this_thread::get_id() << " obj=" << this << " (already started/done)";
    }
 }

@@ -1484,9 +1498,15 @@ bool PrintObject::invalidate_step(PrintObjectStep step)
 		invalidated |= this->invalidate_steps({ posPerimeters, posPrepareInfill, posInfill, posIroning, posContouring, posSupportMaterial, posSimplifyPath, posSimplifyInfill });
        invalidated |= m_print->invalidate_steps({ psSkirtBrim });
        m_slicing_params.valid = false;
+        // The exact belt_floor_z_shift is recomputed when slice() runs again.
+        m_belt_floor_z_shift_cache_valid = false;
    } else if (step == posSupportMaterial) {
        invalidated |= this->invalidate_steps({ posSimplifySupportPath });
        invalidated |= m_print->invalidate_steps({ psSkirtBrim });
+        // SlicingParameters depend on support config (enable_support /
+        // raft_layers / enforce_support_layers feed min/max layer height in
+        // Slicing.cpp), so invalidate them here.  The vertex-scan
+        // belt_floor_z_shift is preserved via m_belt_floor_z_shift_cached.
        m_slicing_params.valid = false;
    }

@@ -1505,6 +1525,7 @@ bool PrintObject::invalidate_all_steps()
    bool result = Inherited::invalidate_all_steps() | m_print->invalidate_all_steps();
 	// Then reset some of the depending values.
 	m_slicing_params.valid = false;
+	m_belt_floor_z_shift_cache_valid = false;
 	return result;
 }

@@ -3733,8 +3754,28 @@ void PrintObject::update_slicing_parameters()
 {
    // Orca: updated function call for XYZ shrinkage compensation
    if (!m_slicing_params.valid) {
-          m_slicing_params = SlicingParameters::create_from_config(this->print()->config(), m_config, this->model_object()->max_z(),
+          coordf_t object_height = this->model_object()->max_z();
+          BeltTransformPipeline::BeltFloorParams belt_floor;
+          const auto &pcfg = this->print()->config();
+          if (pcfg.belt_printer.value) {
+              BoundingBoxf3 bb = BeltTransformPipeline::remap_bbox(*this->model_object(), pcfg);
+              if (BeltTransformPipeline::has_preslice_remap(pcfg))
+                  object_height = bb.size().z();
+              auto hr = BeltTransformPipeline::compute_belt_height_and_floor(pcfg, bb, object_height);
+              object_height = hr.object_height;
+              belt_floor    = hr.floor_params;
+          }
+          m_slicing_params = SlicingParameters::create_from_config(pcfg, m_config, object_height,
                                                                   this->object_extruders(), this->print()->shrinkage_compensation());
+          // Populate belt floor parameters into slicing params for support clipping.
+          m_slicing_params.belt_floor_shear_factor = belt_floor.shear_factor;
+          m_slicing_params.belt_floor_from_axis    = belt_floor.from_axis;
+          m_slicing_params.belt_floor_z_shift     = belt_floor.z_shift;
+          // Prefer the vertex-scan z_shift over the bbox approximation when
+          // slice() has already produced one (e.g. this rebuild was triggered
+          // by a support-config change, which doesn't move the belt floor).
+          if (m_belt_floor_z_shift_cache_valid)
+              m_slicing_params.belt_floor_z_shift = m_belt_floor_z_shift_cached;
      }
 }

@@ -3775,9 +3816,24 @@ SlicingParameters PrintObject::slicing_parameters(const DynamicPrintConfig &full
    sort_remove_duplicates(object_extruders);
    //FIXME add painting extruders

-    if (object_max_z <= 0.f)
-        object_max_z = (float)model_object.raw_bounding_box().size().z();
-    return SlicingParameters::create_from_config(print_config, object_config, object_max_z, object_extruders, object_shrinkage_compensation);
+    BeltTransformPipeline::BeltFloorParams belt_floor;
+    if (object_max_z <= 0.f) {
+        BoundingBoxf3 bb = model_object.raw_bounding_box();
+        object_max_z = (float)bb.size().z();
+        if (print_config.belt_printer.value) {
+            bb = BeltTransformPipeline::remap_bbox(model_object, print_config);
+            if (BeltTransformPipeline::has_preslice_remap(print_config))
+                object_max_z = (float)bb.size().z();
+            auto hr = BeltTransformPipeline::compute_belt_height_and_floor(print_config, bb, object_max_z);
+            object_max_z = (float)hr.object_height;
+            belt_floor   = hr.floor_params;
+        }
+    }
+    SlicingParameters params = SlicingParameters::create_from_config(print_config, object_config, object_max_z, object_extruders, object_shrinkage_compensation);
+    params.belt_floor_shear_factor = belt_floor.shear_factor;
+    params.belt_floor_from_axis    = belt_floor.from_axis;
+    params.belt_floor_z_shift     = belt_floor.z_shift;
+    return params;
 }

 // returns 0-based indices of extruders used to print the object (without brim, support and other helper extrusions)
@@ -4286,6 +4342,67 @@ void PrintObject::combine_infill()
    }
 }

+// Belt printer: clip an ExtrusionEntityCollection to a region defined by clip_expoly.
+// Handles ExtrusionPath, ExtrusionMultiPath, ExtrusionLoop, and nested ExtrusionEntityCollection.
+static void clip_support_fills(ExtrusionEntityCollection &fills, const ExPolygons &clip_region)
+{
+    ExtrusionEntitiesPtr new_entities;
+    for (ExtrusionEntity *entity : fills.entities) {
+        if (auto *path = dynamic_cast<ExtrusionPath *>(entity)) {
+            ExtrusionEntityCollection clipped;
+            path->intersect_expolygons(clip_region, &clipped);
+            if (!clipped.empty()) {
+                for (ExtrusionEntity *e : clipped.entities)
+                    new_entities.push_back(e->clone());
+            }
+            delete entity;
+        } else if (auto *multipath = dynamic_cast<ExtrusionMultiPath *>(entity)) {
+            ExtrusionPaths new_paths;
+            for (const ExtrusionPath &p : multipath->paths) {
+                ExtrusionEntityCollection clipped;
+                p.intersect_expolygons(clip_region, &clipped);
+                for (ExtrusionEntity *e : clipped.entities)
+                    if (auto *cp = dynamic_cast<ExtrusionPath *>(e))
+                        new_paths.push_back(std::move(*cp));
+            }
+            if (!new_paths.empty()) {
+                multipath->paths = std::move(new_paths);
+                new_entities.push_back(multipath);
+            } else {
+                delete entity;
+            }
+        } else if (auto *loop = dynamic_cast<ExtrusionLoop *>(entity)) {
+            ExtrusionPaths new_paths;
+            for (const ExtrusionPath &p : loop->paths) {
+                ExtrusionEntityCollection clipped;
+                p.intersect_expolygons(clip_region, &clipped);
+                for (ExtrusionEntity *e : clipped.entities)
+                    if (auto *cp = dynamic_cast<ExtrusionPath *>(e))
+                        new_paths.push_back(std::move(*cp));
+            }
+            if (!new_paths.empty()) {
+                // Loop is no longer a closed loop after clipping; emit as individual paths.
+                for (auto &p : new_paths)
+                    new_entities.push_back(new ExtrusionPath(std::move(p)));
+                delete entity;
+            } else {
+                delete entity;
+            }
+        } else if (auto *coll = dynamic_cast<ExtrusionEntityCollection *>(entity)) {
+            clip_support_fills(*coll, clip_region);
+            if (!coll->empty()) {
+                new_entities.push_back(coll);
+            } else {
+                delete entity;
+            }
+        } else {
+            // Unknown entity type — keep as-is.
+            new_entities.push_back(entity);
+        }
+    }
+    fills.entities = std::move(new_entities);
+}
+
 void PrintObject::_generate_support_material()
 {
    if (is_tree(m_config.support_type.value)) {
@@ -4297,6 +4414,25 @@ void PrintObject::_generate_support_material()
        PrintObjectSupportMaterial support_material(this, m_slicing_params);
        support_material.generate(*this);
    }
+    // Global Z offset for support layers:
+    // - Normal support: layers already inherit global_z_offset from object layers.
+    // - Non-organic tree support (slim/strong/hybrid): plan_layer_heights() reads
+    //   from globally-offset object layers, so support layers already have it.
+    // - Organic tree support: generate_tree_support_3D() computes its own Z values
+    //   independently and does NOT inherit the offset — apply it here.
+    // Belt floor polygon clipping for non-organic tree support is done inside
+    // draw_circles() before area_groups and toolpaths are built.
+    if (is_tree(m_config.support_type.value) && std::abs(m_belt_global_z_offset) > EPSILON) {
+        // Resolve effective support style (same logic as SupportParameters).
+        auto style = m_config.support_style.value;
+        if (style == smsDefault)
+            style = smsTreeOrganic;
+        if (style == smsTreeOrganic) {
+            for (SupportLayer *sl : m_support_layers)
+                sl->print_z += m_belt_global_z_offset;
+        }
+    }
+
 }

 // BBS
@@ -1,4 +1,6 @@
 #include <boost/log/trivial.hpp>
+#include <limits>
+#include <thread>

 #include <tbb/parallel_for.h>

@@ -9,6 +11,9 @@
 #include "Layer.hpp"
 #include "MultiMaterialSegmentation.hpp"
 #include "Print.hpp"
+#include "BeltTransform.hpp"
+#include "BeltSliceStrategy.hpp"
+#include "Geometry.hpp"
 //BBS
 #include "ShortestPath.hpp"
 #include "libslic3r/Feature/Interlocking/InterlockingGenerator.hpp"
@@ -152,7 +157,8 @@ static std::vector<VolumeSlices> slice_volumes_inner(
    ModelVolumePtrs                                           model_volumes,
    const std::vector<PrintObjectRegions::LayerRangeRegions> &layer_ranges,
    const std::vector<float>                                 &zs,
-    const std::function<void()>                              &throw_on_cancel_callback)
+    const std::function<void()>                              &throw_on_cancel_callback,
+    double                                                   *out_belt_min_z = nullptr)
 {
    model_volumes_sort_by_id(model_volumes);

@@ -167,6 +173,10 @@ static std::vector<VolumeSlices> slice_volumes_inner(
    params_base.closing_radius = print_object_config.slice_closing_radius.value;
    params_base.extra_offset   = 0;
    params_base.trafo          = object_trafo;
+    // Pre-slice mesh transforms: axis remap (standalone — works without belt
+    // mode), belt rotation, and the per-object Z-shift.  Owned by BeltSliceStrategy
+    // so this belt/remap-specific logic stays out of the generic slicing pipeline.
+    BeltSliceStrategy::apply_preslice_transforms(params_base.trafo, print_config, model_volumes, out_belt_min_z);
    //BBS: 0.0025mm is safe enough to simplify the data to speed slicing up for high-resolution model.
    //Also has on influence on arc fitting which has default resolution 0.0125mm.
    params_base.resolution = print_config.resolution <= 0.001 ? 0.0f : 0.0025;
@@ -300,20 +310,47 @@ static std::vector<std::vector<ExPolygons>> slices_to_regions(
                }
            } else {
                zs_complex.reserve(zs.size());
+                // region.bbox is computed in pre-belt-transform slicer space (see PrintApply.cpp::trafo_for_bbox).
+                // When belt transforms are active, layer Z values are in post-rotation/shear/scale/remap space,
+                // so the Z components of region.bbox aren't comparable to z. Skipping the Z filter here
+                // pushes those layers into the parallel_for path below, which handles multi-volume
+                // clipping per layer without relying on the bbox Z range.
+                const bool bbox_z_in_layer_frame = !(print_config.belt_printer.value &&
+                    (BeltTransformPipeline::has_rotation(print_config)
+                        || BeltTransformPipeline::has_preslice_remap(print_config)));
+                // Belt-transform addendum: with bbox-Z untrusted, the simple path's
+                // "first model_part wins" logic drops subsequent volumes' slices unless
+                // they XY-overlap with the first.  Assemblies whose volumes are stacked
+                // or side-by-side in pre-transform Z (different bbox.z ranges) thus lose
+                // the volumes that originally sat outside the first volume's Z range —
+                // showing up as truncation at the top or bottom of the assembly.  Force
+                // every layer in a multi-volume range through the parallel_for path,
+                // which correctly merges all volumes per layer.
+                int num_model_parts = 0;
+                for (const PrintObjectRegions::VolumeRegion &vr : layer_range.volume_regions)
+                    if (vr.model_volume->is_model_part())
+                        ++num_model_parts;
+                const bool force_complex_for_belt = !bbox_z_in_layer_frame && num_model_parts > 1;
                for (; z_idx < zs.size() && zs[z_idx] < layer_range.layer_height_range.second; ++ z_idx) {
                    float z                          = zs[z_idx];
+                    if (force_complex_for_belt) {
+                        zs_complex.push_back({ z_idx, z });
+                        continue;
+                    }
                    int   idx_first_printable_region = -1;
                    bool  complex                    = false;
                    for (int idx_region = 0; idx_region < int(layer_range.volume_regions.size()); ++ idx_region) {
                        const PrintObjectRegions::VolumeRegion &region = layer_range.volume_regions[idx_region];
-                        if (region.bbox->min().z() <= z && region.bbox->max().z() >= z) {
+                        if (!bbox_z_in_layer_frame || (region.bbox->min().z() <= z && region.bbox->max().z() >= z)) {
                            if (idx_first_printable_region == -1 && region.model_volume->is_model_part())
                                idx_first_printable_region = idx_region;
                            else if (idx_first_printable_region != -1) {
                                // Test for overlap with some other region.
                                for (int idx_region2 = idx_first_printable_region; idx_region2 < idx_region; ++ idx_region2) {
                                    const PrintObjectRegions::VolumeRegion &region2 = layer_range.volume_regions[idx_region2];
-                                    if (region2.bbox->min().z() <= z && region2.bbox->max().z() >= z && overlap_in_xy(*region.bbox, *region2.bbox)) {
+                                    const bool region2_in_z = !bbox_z_in_layer_frame
+                                        || (region2.bbox->min().z() <= z && region2.bbox->max().z() >= z);
+                                    if (region2_in_z && overlap_in_xy(*region.bbox, *region2.bbox)) {
                                        complex = true;
                                        break;
                                    }
@@ -816,8 +853,12 @@ void groupingVolumesForBrim(PrintObject* object, LayerPtrs& layers, int firstLay
 // Resulting expolygons of layer regions are marked as Internal.
 void PrintObject::slice()
 {
-    if (! this->set_started(posSlice))
+    BOOST_LOG_TRIVIAL(trace) << "[BELTRACE] slice request tid=" << std::this_thread::get_id() << " obj=" << this;
+    if (! this->set_started(posSlice)) {
+        BOOST_LOG_TRIVIAL(trace) << "[BELTRACE] slice SKIP tid=" << std::this_thread::get_id() << " obj=" << this << " (already started/done)";
        return;
+    }
+    BOOST_LOG_TRIVIAL(trace) << "[BELTRACE] slice ENTER tid=" << std::this_thread::get_id() << " obj=" << this;
    //BBS: add flag to reload scene for shell rendering
    m_print->set_status(5, L("Slicing mesh"), PrintBase::SlicingStatus::RELOAD_SCENE);
    std::vector<coordf_t> layer_height_profile;
@@ -828,6 +869,34 @@ void PrintObject::slice()
    m_layers = new_layers(this, generate_object_layers(m_slicing_params, layer_height_profile, m_config.precise_z_height.value));
    this->slice_volumes();
    m_print->throw_if_canceled();
+
+    // Belt floor Z-shift: where is the belt surface in final slicer space?
+    //
+    // The belt surface is at model_Y=0 (XZ belt plane). After the full
+    // pipeline (trafo_centered → pre_remap → shear → z_shift), the belt
+    // surface equation in slicer space is:
+    //   Z_belt = sf * from_axis + belt_surface_z_centered + z_shift_val
+    //
+    // belt_surface_z_centered = remapped_bbox.min.z() (the Z position of
+    //   the belt surface in centered-pre-shear slicer space, which is 0
+    //   without pre-remap but nonzero when e.g. Y↔Z swap shifts the belt
+    //   surface away from Z=0 by the centering offset).
+    //
+    // z_shift_val = max(0, -m_belt_min_z) (lifts mesh above Z=0).
+    //
+    // So: belt_floor_z_shift = remapped_bb.min.z() + z_shift_val
+    if (std::abs(m_slicing_params.belt_floor_shear_factor) > EPSILON) {
+        double z_shift_val = (m_belt_min_z < 0.) ? -m_belt_min_z : 0.;
+        // With pre-remap, the belt surface (model_Y=0) may not be at Z=0 in
+        // centered slicer space — add the remapped bbox min Z to compensate.
+        // Without pre-remap, the belt surface IS at Z=0 and bb.min.z() is
+        // already folded into m_belt_min_z, so use 0.
+        const auto &pcfg = this->print()->config();
+        double belt_surface_z = BeltTransformPipeline::has_preslice_remap(pcfg)
+            ? BeltTransformPipeline::remap_bbox(*this->model_object(), pcfg).min.z() : 0.;
+        m_slicing_params.belt_floor_z_shift = belt_surface_z + z_shift_val;
+    }
+
    int firstLayerReplacedBy = 0;

 #if 0
@@ -866,7 +935,193 @@ void PrintObject::slice()
    if (m_layers.empty())
        throw Slic3r::SlicingError(L("No layers were detected. You might want to repair your STL file(s) or check their size or thickness and retry.\n"));

+    // Belt printer global mode: offset all layer Z values so objects at
+    // different bed positions print at different heights on the tilted belt.
+    // This is a post-slicing adjustment — the sliced geometry is identical
+    // regardless of global mode, only the output Z coordinates change.
+    {
+        const auto &pcfg = this->print()->config();
+        BOOST_LOG_TRIVIAL(trace) << "Belt global check: belt_printer=" << pcfg.belt_printer.value
+            << " belt_slice_rotation=" << int(pcfg.belt_slice_rotation.value)
+            << " belt_slice_rotation_global=" << pcfg.belt_slice_rotation_global.value
+            << " belt_preslice_global=" << pcfg.belt_preslice_global.value
+            << " object=" << this->model_object()->name;
+        if (pcfg.belt_printer.value) {
+
+            Point inst_shift = this->instances().empty() ? Point(0, 0)
+                : this->instances().front().shift - this->center_offset();
+            BOOST_LOG_TRIVIAL(trace) << "Belt global: object " << this->model_object()->name
+                << " instances=" << this->instances().size()
+                << " shift=(" << unscale<double>(inst_shift.x()) << ", " << unscale<double>(inst_shift.y()) << ")";
+
+            // Per-object Z-shift compensation, applied regardless of global mode.
+            //
+            // BeltSliceStrategy::apply_preslice_transforms lifts the mesh by max(0, -m_belt_min_z)
+            // so the slicer can slice with slicer_z >= 0.  BeltBackTransform inverts
+            // build_forward_transform() which DOES NOT include this per-object
+            // Z-shift (it's not known until vertex scan time).  Result: G-code
+            // coords emerge offset by the un-undone Z-shift — the inverse rotation
+            // couples slicer_z back into both machine_y and machine_z.  Compensating
+            // layer.print_z by belt_z_shift here makes the back-transform produce
+            // correct machine-frame coordinates whether or not a global mode is active.
+            double belt_surface_z = BeltTransformPipeline::has_preslice_remap(pcfg)
+                ? BeltTransformPipeline::remap_bbox(*this->model_object(), pcfg).min.z() : 0.;
+            // The compensation must mirror the Z-shift actually applied, which
+            // is max(0, -m_belt_min_z): when the transformed mesh starts ABOVE
+            // slicer Z=0 (m_belt_min_z > 0 — possible for counter-rotated or
+            // asymmetric geometry whose centered-frame minimum lands positive)
+            // no lift was applied, and an unclamped m_belt_min_z here would
+            // leak straight into the layer Z values, floating the whole object
+            // off the belt by exactly that amount.
+            double belt_z_shift = std::min(m_belt_min_z, 0.) - belt_surface_z;
+            double global_z_offset = belt_z_shift;
+
+            // Centering correction: trafo_centered pretranslates by
+            // -m_center_offset.{x,y}.  Under the belt forward transform, the
+            // Y component of that pretranslate couples into slicer-Z (shear:
+            // tan*c.y, rotation: sin*c.y).  BeltBackTransform inverts the
+            // rotation/shear but doesn't undo centering, so this Z component
+            // leaks into machine output as a position offset whenever
+            // m_center_offset != 0.  When a user moves a volume within an
+            // assembly such that the combined bbox center shifts, this shows
+            // up as a small Z translation in the print.  Compensate by adding
+            // the Z component of the centering through the forward transform.
+            {
+                Transform3d T_fwd = BeltTransformPipeline::build_forward_transform(pcfg);
+                Vec3d c_off(unscale<double>(m_center_offset.x()),
+                            unscale<double>(m_center_offset.y()),
+                            0.);
+                double centering_z_corr = (T_fwd.linear() * c_off).z();
+                global_z_offset += centering_z_corr;
+                BOOST_LOG_TRIVIAL(trace) << "[BELT-DEBUG] centering correction"
+                    << " obj=" << this->model_object()->name
+                    << " m_center_offset_mm=(" << c_off.x() << "," << c_off.y() << ")"
+                    << " centering_z_corr=" << centering_z_corr
+                    << " (added to global_z_offset)";
+            }
+
+            // [BELT-DEBUG] Per-object summary so Case A vs Case B can be compared
+            // side-by-side.  Lays out every value that feeds into the final layer
+            // print_z adjustment.
+            {
+                BoundingBoxf3 raw_bb = this->model_object()->raw_bounding_box();
+                BOOST_LOG_TRIVIAL(trace) << "[BELT-DEBUG] slice() per-object summary"
+                    << " obj=" << this->model_object()->name
+                    << " n_volumes=" << this->model_object()->volumes.size()
+                    << " raw_bbox.min=(" << raw_bb.min.x() << "," << raw_bb.min.y() << "," << raw_bb.min.z() << ")"
+                    << " raw_bbox.max=(" << raw_bb.max.x() << "," << raw_bb.max.y() << "," << raw_bb.max.z() << ")"
+                    << " raw_bbox.center=(" << raw_bb.center().x() << "," << raw_bb.center().y() << ")"
+                    << " m_center_offset=(" << unscale<double>(m_center_offset.x()) << "," << unscale<double>(m_center_offset.y()) << ")"
+                    << " inst_shift=(" << unscale<double>(inst_shift.x()) << "," << unscale<double>(inst_shift.y()) << ")"
+                    << " m_belt_min_z=" << m_belt_min_z
+                    << " belt_surface_z=" << belt_surface_z
+                    << " belt_z_shift=" << belt_z_shift;
+                // Per-volume bbox + get_matrix translation so order/composition is visible.
+                int vi = 0;
+                for (const ModelVolume *mv : this->model_object()->volumes) {
+                    if (!mv->is_model_part()) { ++vi; continue; }
+                    BoundingBoxf3 vol_bb = mv->mesh().transformed_bounding_box(mv->get_matrix());
+                    BOOST_LOG_TRIVIAL(trace) << "[BELT-DEBUG]   vol[" << vi
+                        << "] id=" << mv->id().id << " name='" << mv->name << "'"
+                        << " get_matrix.translation=(" << mv->get_matrix().translation().x() << "," << mv->get_matrix().translation().y() << "," << mv->get_matrix().translation().z() << ")"
+                        << " object_bbox.min=(" << vol_bb.min.x() << "," << vol_bb.min.y() << "," << vol_bb.min.z() << ")"
+                        << " object_bbox.max=(" << vol_bb.max.x() << "," << vol_bb.max.y() << "," << vol_bb.max.z() << ")";
+                    ++vi;
+                }
+            }
+
+            if (pcfg.belt_preslice_global.value) {
+                // Global pre-slice mode: compute full correction c = (T.linear() - I) * d
+                // where T is the belt forward transform and d is the bed position.
+                Transform3d T = BeltTransformPipeline::build_forward_transform(pcfg);
+                Vec3d d(unscale<double>(inst_shift.x()), unscale<double>(inst_shift.y()), 0.);
+                Vec3d c = T.linear() * d - d;
+                global_z_offset += c.z();
+                BOOST_LOG_TRIVIAL(trace) << "[BELTRACE] write m_belt_global_xy_correction tid=" << std::this_thread::get_id()
+                    << " obj=" << this << " old=(" << m_belt_global_xy_correction.x() << "," << m_belt_global_xy_correction.y()
+                    << ") new=(" << c.x() << "," << c.y() << ")";
+                m_belt_global_xy_correction = Vec2d(c.x(), c.y());
+
+                BOOST_LOG_TRIVIAL(trace) << "Belt preslice_global: correction=("
+                    << c.x() << ", " << c.y() << ", " << c.z() << ")"
+                    << " belt_z_shift=" << belt_z_shift << " (m_belt_min_z=" << m_belt_min_z << ")";
+            } else {
+                // Slicing rotation in global mode: bed-position-dependent Z offset.
+                // For R(α, X): c.z = sin(α)*d.y so objects at different bed-Y
+                // values print at different machine Z values along the inclined belt.
+                if (pcfg.belt_slice_rotation_global.value
+                    && pcfg.belt_slice_rotation.value != BeltRotationAxis::None
+                    && std::abs(pcfg.belt_slice_rotation_angle.value) > EPSILON) {
+                    Transform3d T = BeltTransformPipeline::build_forward_transform(pcfg);
+                    Vec3d d(unscale<double>(inst_shift.x()), unscale<double>(inst_shift.y()), 0.);
+                    Vec3d c = T.linear() * d - d;
+                    global_z_offset += c.z();
+                    m_belt_global_xy_correction = Vec2d(c.x(), c.y());
+                }
+
+                // Pre-slice remap global mode: when on, the remap accounts for the
+                // instance bed position. The Z component of the correction
+                // (R - I) * d shifts layer print_z so e.g. a Y↔Z swap with an
+                // object at Y=50 prints at Z=50.
+                if (pcfg.preslice_remap_global.value
+                    && BeltTransformPipeline::has_preslice_remap(pcfg)) {
+                    Transform3d R = BeltTransformPipeline::build_preslice_remap(pcfg);
+                    Vec3d d(unscale<double>(inst_shift.x()), unscale<double>(inst_shift.y()), 0.);
+                    Vec3d remap_correction = R.linear() * d - d;
+                    global_z_offset += remap_correction.z();
+                }
+            }
+
+            BOOST_LOG_TRIVIAL(trace) << "Belt global: z_offset=" << global_z_offset
+                << " (relative to min across " << this->print()->objects().size() << " objects)";
+            BOOST_LOG_TRIVIAL(trace) << "[BELTRACE] write m_belt_global_z_offset tid=" << std::this_thread::get_id()
+                << " obj=" << this << " old=" << m_belt_global_z_offset << " new=" << global_z_offset;
+            m_belt_global_z_offset = global_z_offset;
+            // [BELT-DEBUG] Final breakdown of all contributions to layer.print_z
+            // and where the first / last layer end up post-adjustment.
+            BOOST_LOG_TRIVIAL(trace) << "[BELT-DEBUG] global_z_offset breakdown"
+                << " obj=" << this->model_object()->name
+                << " belt_z_shift=" << belt_z_shift
+                << " total_global_z_offset=" << global_z_offset
+                << " xy_correction=(" << m_belt_global_xy_correction.x() << "," << m_belt_global_xy_correction.y() << ")"
+                << " belt_floor_z_shift_before=" << (m_slicing_params.belt_floor_z_shift)
+                << " n_layers=" << m_layers.size();
+            if (std::abs(global_z_offset) > EPSILON) {
+                for (Layer *layer : m_layers)
+                    layer->print_z += global_z_offset;
+                // Keep belt floor clipping in sync with the shifted print_z
+                // values — the support generator sees globally-offset object
+                // layer print_z, so belt_floor_z_shift must match.
+                m_slicing_params.belt_floor_z_shift += global_z_offset;
+            }
+            if (!m_layers.empty()) {
+                BOOST_LOG_TRIVIAL(trace) << "[BELT-DEBUG]   post-adjustment"
+                    << " first_layer.print_z=" << m_layers.front()->print_z
+                    << " last_layer.print_z=" << m_layers.back()->print_z
+                    << " belt_floor_z_shift_after=" << m_slicing_params.belt_floor_z_shift;
+            }
+            if (!m_layers.empty()) {
+                BOOST_LOG_TRIVIAL(trace) << "Belt global: first_layer_z=" << m_layers.front()->print_z
+                    << " last_layer_z=" << m_layers.back()->print_z
+                    << " num_layers=" << m_layers.size()
+                    << " center_offset=(" << unscale<double>(m_center_offset.x())
+                    << ", " << unscale<double>(m_center_offset.y()) << ")";
+            }
+
+            // Cache the final patched belt_floor_z_shift so a later support-only
+            // invalidation can rebuild m_slicing_params without losing this exact
+            // (vertex-scan-derived) value.  update_slicing_parameters() will
+            // restore it after create_from_config() seeds the bbox approximation.
+            m_belt_floor_z_shift_cached      = m_slicing_params.belt_floor_z_shift;
+            m_belt_floor_z_shift_cache_valid = true;
+        }
+    }
+
    // BBS
+    BOOST_LOG_TRIVIAL(trace) << "[BELTRACE] slice EXIT tid=" << std::this_thread::get_id() << " obj=" << this
+        << " layers=" << m_layers.size() << " belt_min_z=" << m_belt_min_z
+        << " belt_global_z_offset=" << m_belt_global_z_offset
+        << " belt_xy=(" << m_belt_global_xy_correction.x() << "," << m_belt_global_xy_correction.y() << ")";
    this->set_done(posSlice);
 }

@@ -1170,7 +1425,8 @@ void PrintObject::slice_volumes()
    if (!slice_zs.empty()) {
        objSliceByVolume = slice_volumes_inner(
            print->config(), this->config(), this->trafo_centered(),
-            this->model_object()->volumes, m_shared_regions->layer_ranges, slice_zs, throw_on_cancel_callback);
+            this->model_object()->volumes, m_shared_regions->layer_ranges, slice_zs, throw_on_cancel_callback,
+            &m_belt_min_z);
    }

    //BBS: "model_part" volumes are grouded according to their connections
@@ -111,6 +111,13 @@ struct SlicingParameters
     coordf_t     object_print_z_uncompensated_max { 0 };
     // Scaling factor for compensating shrinkage in Z-axis.
     coordf_t    object_shrinkage_compensation_z { 0 };
+
+    // Belt printer: floor plane parameters for support clipping.
+    // Belt contact surface in slicing coords: Z = bb_min_z + sf*Y + slicing_z_shift.
+    // cutoff = (print_z - belt_floor_z_shift - floor_offset) / shear_factor
+    double      belt_floor_shear_factor { 0.0 };  // shear factor (e.g. cot(45deg))
+    int         belt_floor_from_axis { 1 };        // which axis the shear is from (0=X, 1=Y)
+    double      belt_floor_z_shift { 0.0 };        // bb_min_z + max(0, -min_z_after_shear)
 };
 static_assert(IsTriviallyCopyable<SlicingParameters>::value, "SlicingParameters class is not POD (and it should be - see constructor).");

@@ -0,0 +1,124 @@
+#include "BeltFloorContext.hpp"
+
+#include <cmath>
+#include <limits>
+
+namespace Slic3r {
+
+bool BeltFloorContext::init(const SlicingParameters &sp, const PrintConfig &pcfg)
+{
+    m_active = false;
+    m_shear_factor = sp.belt_floor_shear_factor;
+    m_from_axis    = sp.belt_floor_from_axis;
+    m_z_shift      = sp.belt_floor_z_shift;
+    m_floor_offset = pcfg.belt_support_floor_offset.value;
+
+    if (std::abs(m_shear_factor) < EPSILON)
+        return false;
+
+    m_active = true;
+    return true;
+}
+
+bool BeltFloorContext::init_local(const SlicingParameters &sp, const PrintConfig &pcfg,
+                                  double global_z_offset)
+{
+    if (!init(sp, pcfg))
+        return false;
+    // Local Z: subtract the global Z offset so polygon computation
+    // works in the object's local coordinate space.
+    m_z_shift -= global_z_offset;
+    return true;
+}
+
+Polygons BeltFloorContext::surface_polygon(coordf_t print_z) const
+{
+    return half_plane(print_z, /*belt_surface=*/true);
+}
+
+Polygons BeltFloorContext::valid_region_polygon(coordf_t print_z) const
+{
+    return half_plane(print_z, /*belt_surface=*/false);
+}
+
+double BeltFloorContext::floor_print_z(const Point &pos_slicing) const
+{
+    if (!m_active)
+        return -std::numeric_limits<double>::infinity();
+    double pos = unscale<double>(m_from_axis == 0 ? pos_slicing.x() : pos_slicing.y());
+    return m_shear_factor * pos + m_floor_offset + m_z_shift;
+}
+
+std::vector<Polygons> BeltFloorContext::compute_per_layer_floors(
+    size_t num_layers,
+    const std::function<double(size_t)> &layer_print_z) const
+{
+    std::vector<Polygons> result(num_layers);
+    if (!m_active)
+        return result;
+    for (size_t i = 0; i < num_layers; ++i)
+        result[i] = surface_polygon(layer_print_z(i));
+    return result;
+}
+
+Polygons BeltFloorContext::half_plane(coordf_t print_z, bool belt_surface) const
+{
+    if (!m_active)
+        return {};
+
+    const double cutoff = (print_z - m_z_shift - m_floor_offset) / m_shear_factor;
+    const coord_t cutoff_scaled = scale_(cutoff);
+    const coord_t large_bound   = scale_(1e3);
+
+    // The belt surface is on one side of the cutoff line; the valid region
+    // is on the other side.  Which side depends on shear_factor sign.
+    //
+    // belt_surface=true  → the belt side (where support should NOT exist)
+    // belt_surface=false → the valid side (where support IS allowed)
+    //
+    // For shear_factor > 0: belt surface is from_axis >= cutoff
+    // For shear_factor < 0: belt surface is from_axis <= cutoff
+    bool high_side = (m_shear_factor > 0) == belt_surface;
+
+    Polygon poly;
+    if (m_from_axis == 0) {
+        if (high_side) {
+            // X >= cutoff
+            poly.points = {
+                Point(cutoff_scaled, -large_bound),
+                Point(large_bound,   -large_bound),
+                Point(large_bound,    large_bound),
+                Point(cutoff_scaled,  large_bound)
+            };
+        } else {
+            // X < cutoff
+            poly.points = {
+                Point(-large_bound,  -large_bound),
+                Point(cutoff_scaled, -large_bound),
+                Point(cutoff_scaled,  large_bound),
+                Point(-large_bound,   large_bound)
+            };
+        }
+    } else {
+        if (high_side) {
+            // Y >= cutoff
+            poly.points = {
+                Point(-large_bound, cutoff_scaled),
+                Point( large_bound, cutoff_scaled),
+                Point( large_bound, large_bound),
+                Point(-large_bound, large_bound)
+            };
+        } else {
+            // Y < cutoff
+            poly.points = {
+                Point(-large_bound, -large_bound),
+                Point( large_bound, -large_bound),
+                Point( large_bound, cutoff_scaled),
+                Point(-large_bound, cutoff_scaled)
+            };
+        }
+    }
+    return { poly };
+}
+
+} // namespace Slic3r
@@ -0,0 +1,74 @@
+#pragma once
+
+#include "../libslic3r.h"
+#include "../Point.hpp"
+#include "../Polygon.hpp"
+#include "../Slicing.hpp"
+#include "../PrintConfig.hpp"
+
+namespace Slic3r {
+
+class PrintObject;
+
+// Belt floor context: encapsulates the parameters and polygon computation
+// for belt printer floor clipping in support generation.
+//
+// All belt floor code across SupportMaterial, TreeSupport, TreeSupport3D,
+// and TreeModelVolumes uses the same 4 parameters and the same 4-case
+// polygon construction.  This class consolidates that logic.
+//
+// Construct once per PrintObject, then call surface_polygon() or
+// valid_region_polygon() per layer with the layer's print_z.
+class BeltFloorContext
+{
+public:
+    BeltFloorContext() = default;
+
+    // Initialize from slicing parameters and print config.
+    // Uses global Z coordinates (for SupportMaterial, non-organic TreeSupport).
+    bool init(const SlicingParameters &sp, const PrintConfig &pcfg);
+
+    // Initialize with a Z offset subtracted from z_shift.
+    // Uses local Z coordinates (for TreeSupport3D, TreeModelVolumes organic pipeline).
+    bool init_local(const SlicingParameters &sp, const PrintConfig &pcfg,
+                    double global_z_offset);
+
+    bool is_active() const { return m_active; }
+
+    // Compute the belt-side half-plane polygon at a given print_z.
+    // This is the region where the belt surface exists.
+    Polygons surface_polygon(coordf_t print_z) const;
+
+    // Compute the valid-region half-plane polygon at a given print_z.
+    // This is the complement: the region where support is allowed.
+    Polygons valid_region_polygon(coordf_t print_z) const;
+
+    // Compute the belt floor Z position at a given XY position (in slicing coords).
+    // Returns -infinity if not active.
+    double floor_print_z(const Point &pos_slicing) const;
+
+    // Pre-compute belt floor polygons for a range of layers.
+    // layer_print_z(i) returns the print_z for layer index i.
+    std::vector<Polygons> compute_per_layer_floors(
+        size_t num_layers,
+        const std::function<double(size_t)> &layer_print_z) const;
+
+    // Accessors
+    double shear_factor()  const { return m_shear_factor; }
+    int    from_axis()     const { return m_from_axis; }
+    double z_shift()       const { return m_z_shift; }
+    double floor_offset()  const { return m_floor_offset; }
+
+private:
+    bool   m_active       = false;
+    double m_shear_factor = 0.0;
+    int    m_from_axis    = 1;  // 0=X, 1=Y
+    double m_z_shift      = 0.0;
+    double m_floor_offset = 0.0;
+
+    // Internal: compute the raw half-plane polygon.
+    // If belt_surface=true, returns the belt side; otherwise the valid (complement) side.
+    Polygons half_plane(coordf_t print_z, bool belt_surface) const;
+};
+
+} // namespace Slic3r
@@ -144,6 +144,12 @@ int idx_lower_or_equal(const std::vector<T*> &vec, int idx, FN_LOWER_EQUAL fn_lo
    return idx_lower_or_equal(vec.begin(), vec.end(), idx, fn_lower_equal);
 }

+// Belt floor: compute the belt-side half-plane polygon at a given print_z.
+// Used to clip support polygons against the belt surface.
+Polygons belt_floor_surface_polygon(
+    const SlicingParameters &slicing_params, const PrintConfig &print_config,
+    const PrintObject &object, coordf_t print_z);
+
 } // namespace Slic3r

 #endif /* slic3r_SupportCommon_hpp_ */
@@ -5,6 +5,7 @@
 #include "Print.hpp"
 #include "SupportMaterial.hpp"
 #include "SupportCommon.hpp"
+#include "BeltFloorContext.hpp"
 #include "Geometry.hpp"
 #include "Point.hpp"
 #include "MutablePolygon.hpp"
@@ -367,10 +368,21 @@ inline void layers_append(SupportGeneratorLayersPtr &dst, const SupportGenerator
 }

 // Support layer that is covered by some form of dense interface.
-static constexpr const std::initializer_list<SupporLayerType> support_types_interface { 
+static constexpr const std::initializer_list<SupporLayerType> support_types_interface {
    SupporLayerType::RaftInterface, SupporLayerType::BottomContact, SupporLayerType::BottomInterface, SupporLayerType::TopContact, SupporLayerType::TopInterface
 };

+// Forward declarations for belt floor helpers (defined later in this file).
+// belt_floor_surface_polygon is declared in SupportCommon.hpp (non-static,
+// shared with TreeSupport.cpp).
+
+static Polygons belt_floor_valid_region_polygon(
+    const SlicingParameters &slicing_params, const PrintConfig &print_config,
+    const PrintObject &object, coordf_t print_z);
+static void trim_support_layers_by_belt_floor(
+    const SlicingParameters &slicing_params, const PrintConfig &print_config,
+    const PrintObject &object, SupportGeneratorLayersPtr &support_layers);
+
 void PrintObjectSupportMaterial::generate(PrintObject &object)
 {
    BOOST_LOG_TRIVIAL(info) << "Support generator - Start";
@@ -443,11 +455,12 @@ void PrintObjectSupportMaterial::generate(PrintObject &object)
        object, bottom_contacts, top_contacts, layer_storage);

    this->trim_support_layers_by_object(object, top_contacts, m_slicing_params.gap_support_object, m_slicing_params.gap_object_support, m_support_params.gap_xy);
+    trim_support_layers_by_belt_floor(m_slicing_params, *m_print_config, object, top_contacts);

 #ifdef SLIC3R_DEBUG
    for (const SupportGeneratorLayer *layer : top_contacts)
        Slic3r::SVG::export_expolygons(
-            debug_out_path("support-top-contacts-trimmed-by-object-%d-%lf.svg", iRun, layer->print_z), 
+            debug_out_path("support-top-contacts-trimmed-by-object-%d-%lf.svg", iRun, layer->print_z),
            union_ex(layer->polygons));
 #endif

@@ -603,6 +616,37 @@ Polygons collect_region_slices_by_type(const Layer &layer, SurfaceType surface_t
    return out;
 }

+// Belt printer: compute the belt-side half-plane polygon at a given print_z.
+// This represents the region where the belt surface exists (the "phantom top surface").
+// Support that overlaps with this polygon should terminate with a bottom contact.
+// Returns empty if belt floor is not active.
+Polygons belt_floor_surface_polygon(
+    const SlicingParameters &slicing_params,
+    const PrintConfig       &print_config,
+    const PrintObject       &object,
+    coordf_t                 print_z)
+{
+    BeltFloorContext ctx;
+    if (!ctx.init(slicing_params, print_config))
+        return {};
+    return ctx.surface_polygon(print_z);
+}
+
+// Belt printer: compute the valid-region half-plane polygon at a given print_z.
+// This is the region where support is allowed to exist (above the belt).
+// Used to clip the downward-propagating support projection.
+static Polygons belt_floor_valid_region_polygon(
+    const SlicingParameters &slicing_params,
+    const PrintConfig       &print_config,
+    const PrintObject       &object,
+    coordf_t                 print_z)
+{
+    BeltFloorContext ctx;
+    if (!ctx.init(slicing_params, print_config))
+        return {};
+    return ctx.valid_region_polygon(print_z);
+}
+
 // Collect outer contours of all slices of this layer.
 // This is useful for calculating the support base with holes filled.
 Polygons collect_slices_outer(const Layer &layer)
@@ -1394,6 +1438,10 @@ static inline ExPolygons detect_overhangs(
    const double threshold_rad = Geometry::deg2rad(thresh_angle);
    const bool bridge_no_support = object_config.bridge_no_support.value;
    const coordf_t xy_expansion = scale_(object_config.support_expansion.value);
+    // Build plate tilt: compute per-layer XY shift for tilted gravity direction
+    const double tilt_x_rad = Geometry::deg2rad(print_config.build_plate_tilt_x.value);
+    const double tilt_y_rad = Geometry::deg2rad(print_config.build_plate_tilt_y.value);
+    const bool   has_tilt   = std::abs(tilt_x_rad) > EPSILON || std::abs(tilt_y_rad) > EPSILON;
    float lower_layer_offset = 0;

    if (layer_id == 0)
@@ -1443,9 +1491,17 @@ static inline ExPolygons detect_overhangs(
            // Overhang polygons for this layer and region.
            Polygons diff_polygons;
            Polygons layerm_polygons = to_polygons(layerm->slices.surfaces);
+            // Apply build plate tilt: shift lower layer polygons to simulate tilted gravity
+            Polygons effective_lower = lower_layer_polygons;
+            if (has_tilt) {
+                const double lh = lower_layer.height;
+                Point tilt_shift(coord_t(scale_(lh * tan(tilt_y_rad))),
+                                 coord_t(scale_(lh * tan(tilt_x_rad))));
+                translate(effective_lower, tilt_shift);
+            }
            if (lower_layer_offset == 0.f) {
                // Support everything.
-                diff_polygons = diff(layerm_polygons, lower_layer_polygons);
+                diff_polygons = diff(layerm_polygons, effective_lower);
                if (buildplate_only) {
                    // Don't support overhangs above the top surfaces.
                    // This step is done before the contact surface is calculated by growing the overhang region.
@@ -1454,9 +1510,9 @@ static inline ExPolygons detect_overhangs(
            } else if (auto_normal_support) {
                // Get the regions needing a suport, collapse very tiny spots.
                //FIXME cache the lower layer offset if this layer has multiple regions.
-                diff_polygons = 
+                diff_polygons =
                    diff(layerm_polygons,
-                            expand(lower_layer_polygons, lower_layer_offset, SUPPORT_SURFACES_OFFSET_PARAMETERS));
+                            expand(effective_lower, lower_layer_offset, SUPPORT_SURFACES_OFFSET_PARAMETERS));
                if (buildplate_only && ! annotations.buildplate_covered[layer_id].empty()) {
                    // Don't support overhangs above the top surfaces.
                    // This step is done before the contact surface is calculated by growing the overhang region.
@@ -1464,9 +1520,9 @@ static inline ExPolygons detect_overhangs(
                }
                if (! diff_polygons.empty()) {
                    // Offset the support regions back to a full overhang, restrict them to the full overhang.
-                    // This is done to increase size of the supporting columns below, as they are calculated by 
+                    // This is done to increase size of the supporting columns below, as they are calculated by
                    // propagating these contact surfaces downwards.
-                    diff_polygons = diff(intersection(expand(diff_polygons, lower_layer_offset, SUPPORT_SURFACES_OFFSET_PARAMETERS), layerm_polygons), lower_layer_polygons);
+                    diff_polygons = diff(intersection(expand(diff_polygons, lower_layer_offset, SUPPORT_SURFACES_OFFSET_PARAMETERS), layerm_polygons), effective_lower);
                }
                //FIXME add user defined filtering here based on minimal area or minimum radius or whatever.

@@ -2506,6 +2562,82 @@ static inline SupportGeneratorLayer* detect_bottom_contacts(
    return &layer_new;
 }

+// Belt printer: detect bottom contacts where support meets the belt floor plane.
+// Modeled on detect_bottom_contacts() but uses the belt plane polygon instead of stTop surfaces.
+static inline SupportGeneratorLayer* detect_belt_floor_bottom_contacts(
+    const SlicingParameters                          &slicing_params,
+    const SupportParameters                          &support_params,
+    const PrintConfig                                &print_config,
+    const PrintObject                                &object,
+    const Layer                                      &layer,
+    // Existing top contact layers, for snapping.
+    const SupportGeneratorLayersPtr                  &top_contacts,
+    size_t                                            contact_idx,
+    SupportGeneratorLayerStorage                     &layer_storage,
+    std::vector<Polygons>                            &layer_support_areas,
+    const Polygons                                   &supports_projected)
+{
+    // Compute the belt surface polygon at this layer's Z.
+    Polygons belt_surface = belt_floor_surface_polygon(slicing_params, print_config, object, layer.print_z);
+    if (belt_surface.empty())
+        return nullptr;
+
+    // Find where projected support overlaps the belt surface.
+    Polygons touching = intersection(belt_surface, supports_projected);
+    if (touching.empty())
+        return nullptr;
+
+    assert(layer.id() >= slicing_params.raft_layers());
+    size_t layer_id = layer.id() - slicing_params.raft_layers();
+
+    // Allocate a new bottom contact layer resting on the belt plane.
+    SupportGeneratorLayer &layer_new = layer_storage.allocate_unguarded(SupporLayerType::BottomContact);
+
+    // No object layer to sync with -- compute heights directly from flow parameters.
+    layer_new.height  = support_params.support_material_bottom_interface_flow.height();
+    layer_new.print_z = layer.print_z + layer_new.height + slicing_params.gap_object_support;
+    layer_new.bottom_z = layer.print_z;
+    layer_new.idx_object_layer_below = layer_id;
+    layer_new.bridging = ! slicing_params.zero_gap_interface_bottom && object.config().thick_bridges;
+    layer_new.polygons = expand(touching, float(support_params.support_material_flow.scaled_width()), SUPPORT_SURFACES_OFFSET_PARAMETERS);
+
+    if (! slicing_params.zero_gap_interface_bottom) {
+        // Snap to nearby top contact layers to avoid very thin support layers.
+        for (size_t top_idx = size_t(std::max<int>(0, int(contact_idx)));
+            top_idx < top_contacts.size() && top_contacts[top_idx]->print_z < layer_new.print_z + support_params.support_layer_height_min + EPSILON;
+            ++ top_idx) {
+            if (top_contacts[top_idx]->print_z > layer_new.print_z - support_params.support_layer_height_min - EPSILON) {
+                coordf_t diff = layer_new.print_z - top_contacts[top_idx]->print_z;
+                assert(std::abs(diff) <= support_params.support_layer_height_min + EPSILON);
+                if (diff > 0.F) {
+                    if (layer_new.height - diff > support_params.support_layer_height_min) {
+                        layer_new.print_z = top_contacts[top_idx]->print_z;
+                        layer_new.height -= diff;
+                    } else {
+                        continue;
+                    }
+                } else {
+                    layer_new.print_z = top_contacts[top_idx]->print_z;
+                    layer_new.height -= diff;
+                }
+                break;
+            }
+        }
+    }
+
+    // Trim the already created base layers above this belt contact.
+    touching = expand(touching, float(SCALED_EPSILON));
+    for (int layer_id_above = int(layer_id) + 1; layer_id_above < int(object.total_layer_count()); ++ layer_id_above) {
+        const Layer &layer_above = *object.layers()[layer_id_above];
+        if (layer_above.print_z > layer_new.print_z - EPSILON)
+            break;
+        if (Polygons &above = layer_support_areas[layer_id_above]; ! above.empty())
+            above = diff(above, touching);
+    }
+
+    return &layer_new;
+}
+
 // Returns polygons to print + polygons to propagate downwards.
 // Called twice: First for normal supports, possibly trimmed by "on build plate only", second for support enforcers not trimmed by "on build plate only".
 static inline std::pair<Polygons, Polygons> project_support_to_grid(const Layer &layer, const SupportGridParams &grid_params, const Polygons &overhangs, Polygons *layer_buildplate_covered
@@ -2605,6 +2737,8 @@ SupportGeneratorLayersPtr PrintObjectSupportMaterial::bottom_contact_layers_and_
    //const auto   expansion_to_slice = m_support_material_flow.scaled_spacing() / 2 + 25;
    const SupportGridParams grid_params(*m_object_config, m_support_params.support_material_flow);
    const bool buildplate_only = ! buildplate_covered.empty();
+    const bool has_belt_floor  = std::abs(m_slicing_params.belt_floor_shear_factor) > EPSILON
+        && m_print_config->belt_support_floor_mode.value == BeltSupportFloorMode::GeneratorOnly;

    // Allocate empty surface areas, one per object layer.
    layer_support_areas.assign(object.total_layer_count(), Polygons());
@@ -2665,8 +2799,9 @@ SupportGeneratorLayersPtr PrintObjectSupportMaterial::bottom_contact_layers_and_
        tbb::task_group task_group;
        const Polygons &overhangs_for_bottom_contacts = buildplate_only ? enforcers_projection_raw : overhangs_projection_raw;
        if (! overhangs_for_bottom_contacts.empty())
-            // Find the bottom contact layers above the top surfaces of this layer.
-            task_group.run([this, &object, &layer, &top_contacts, contact_idx, &layer_storage, &layer_support_areas, &bottom_contacts, &overhangs_for_bottom_contacts
+            // Find the bottom contact layers above the top surfaces of this layer,
+            // and also detect belt floor contacts if belt mode is active.
+            task_group.run([this, &object, &layer, &top_contacts, contact_idx, &layer_storage, &layer_support_areas, &bottom_contacts, &overhangs_for_bottom_contacts, has_belt_floor
    #ifdef SLIC3R_DEBUG
                , iRun, &polygons_new
    #endif // SLIC3R_DEBUG
@@ -2680,6 +2815,15 @@ SupportGeneratorLayersPtr PrintObjectSupportMaterial::bottom_contact_layers_and_
                    );
                    if (layer_new)
                        bottom_contacts.push_back(layer_new);
+                    // Belt floor phantom surface: detect where support meets the belt plane.
+                    if (has_belt_floor) {
+                        SupportGeneratorLayer *belt_layer = detect_belt_floor_bottom_contacts(
+                            m_slicing_params, m_support_params, *m_print_config, object,
+                            layer, top_contacts, contact_idx, layer_storage,
+                            layer_support_areas, overhangs_for_bottom_contacts);
+                        if (belt_layer)
+                            bottom_contacts.push_back(belt_layer);
+                    }
                });

        Polygons &layer_support_area = layer_support_areas[layer_id];
@@ -2718,6 +2862,23 @@ SupportGeneratorLayersPtr PrintObjectSupportMaterial::bottom_contact_layers_and_

        task_group.wait();

+        // Belt floor: clip projections and support areas so support doesn't
+        // propagate below the belt plane.
+        if (has_belt_floor) {
+            Polygons valid_region = belt_floor_valid_region_polygon(
+                m_slicing_params, *m_print_config, object, layer.print_z);
+            if (! valid_region.empty()) {
+                if (! overhangs_projection.empty())
+                    overhangs_projection = intersection(overhangs_projection, valid_region);
+                if (! enforcers_projection.empty())
+                    enforcers_projection = intersection(enforcers_projection, valid_region);
+                if (! layer_support_area.empty())
+                    layer_support_area = intersection(layer_support_area, valid_region);
+                if (! layer_support_area_enforcers.empty())
+                    layer_support_area_enforcers = intersection(layer_support_area_enforcers, valid_region);
+            }
+        }
+
        if (! layer_support_area_enforcers.empty()) {
            if (layer_support_area.empty())
                layer_support_area = std::move(layer_support_area_enforcers);
@@ -2728,6 +2889,7 @@ SupportGeneratorLayersPtr PrintObjectSupportMaterial::bottom_contact_layers_and_

    std::reverse(bottom_contacts.begin(), bottom_contacts.end());
    trim_support_layers_by_object(object, bottom_contacts, m_slicing_params.gap_support_object, m_slicing_params.gap_object_support, m_support_params.gap_xy);
+    trim_support_layers_by_belt_floor(m_slicing_params, *m_print_config, object, bottom_contacts);
    return bottom_contacts;
 }

@@ -3101,6 +3263,33 @@ void PrintObjectSupportMaterial::generate_base_layers(
 #endif /* SLIC3R_DEBUG */

    this->trim_support_layers_by_object(object, intermediate_layers, m_slicing_params.gap_support_object, m_slicing_params.gap_object_support, m_support_params.gap_xy);
+    trim_support_layers_by_belt_floor(m_slicing_params, *m_print_config, object, intermediate_layers);
+}
+
+// Belt printer: trim support layer polygons by the belt floor plane.
+// For each support layer, computes the belt floor half-plane at that layer's print_z
+// and subtracts it from the support polygons. This follows the same diff() pattern
+// as trim_support_layers_by_object() so that interface layers derived from trimmed
+// intermediates automatically inherit the belt floor trimming.
+static void trim_support_layers_by_belt_floor(
+    const SlicingParameters          &slicing_params,
+    const PrintConfig                &print_config,
+    const PrintObject                &object,
+    SupportGeneratorLayersPtr        &support_layers)
+{
+    BeltFloorContext ctx;
+    if (!ctx.init(slicing_params, print_config))
+        return;
+    if (print_config.belt_support_floor_mode.value != BeltSupportFloorMode::GeneratorOnly)
+        return;
+
+    tbb::parallel_for(tbb::blocked_range<size_t>(0, support_layers.size()),
+        [&](const tbb::blocked_range<size_t> &range) {
+            for (size_t i = range.begin(); i < range.end(); ++i)
+                if (support_layers[i])
+                    support_layers[i]->polygons = diff(support_layers[i]->polygons,
+                                                       ctx.surface_polygon(support_layers[i]->print_z));
+        });
 }

 void PrintObjectSupportMaterial::trim_support_layers_by_object(
@@ -8,6 +8,7 @@

 #include "TreeModelVolumes.hpp"
 #include "TreeSupportCommon.hpp"
+#include "BeltFloorContext.hpp"

 #include "../BuildVolume.hpp"
 #include "../ClipperUtils.hpp"
@@ -94,6 +95,29 @@ TreeModelVolumes::TreeModelVolumes(
 #else
    {
        m_anti_overhang = print_object.slice_support_blockers();
+        // Belt floor: add belt surface polygons to anti_overhang so support
+        // is never generated inside the belt.  Only in global shear mode —
+        // in local mode the belt floor clipping handles everything and
+        // anti_overhang at the bottom layers would block all support.
+        {
+            const auto &sp   = print_object.slicing_parameters();
+            const auto &pcfg = print_object.print()->config();
+            BeltFloorContext ctx;
+            ctx.init_local(sp, pcfg, print_object.belt_global_z_offset());
+            if (ctx.is_active()
+                && std::abs(print_object.belt_global_z_offset()) > EPSILON
+                && pcfg.belt_support_floor_mode.value == BeltSupportFloorMode::GeneratorOnly) {
+                size_t num_layers_needed = print_object.layer_count();
+                // Ensure m_anti_overhang is large enough.
+                if (m_anti_overhang.size() < num_layers_needed)
+                    m_anti_overhang.resize(num_layers_needed, Polygons{});
+                for (size_t layer_idx = 0; layer_idx < num_layers_needed; ++layer_idx) {
+                    double print_z = print_object.get_layer(layer_idx)->print_z
+                                   - print_object.belt_global_z_offset();
+                    append(m_anti_overhang[layer_idx], ctx.surface_polygon(print_z));
+                }
+            }
+        }
        TreeSupportMeshGroupSettings mesh_settings(print_object);
        const TreeSupportSettings config{ mesh_settings, print_object.slicing_parameters() };
        m_current_min_xy_dist = config.xy_min_distance;
@@ -102,6 +126,27 @@ TreeModelVolumes::TreeModelVolumes(
        m_increase_until_radius = config.increase_radius_until_radius;
        m_radius_0 = config.getRadius(0);
        m_raft_layers = config.raft_layers;
+        // Belt printer: add virtual belt raft layers below the object, matching
+        // the extra layers added in generate_support_areas() so both use the
+        // same layer indexing.
+        {
+            const auto &sp2   = print_object.slicing_parameters();
+            const auto &pcfg2 = print_object.print()->config();
+            double belt_sf = sp2.belt_floor_shear_factor;
+            if (std::abs(belt_sf) > EPSILON && std::abs(print_object.belt_global_z_offset()) > EPSILON
+                && pcfg2.belt_support_floor_mode.value == BeltSupportFloorMode::GeneratorOnly) {
+                double bb_min_z    = std::abs(belt_remapped_bbox(*print_object.model_object(), pcfg2).min.z());
+                double extra_depth = bb_min_z + 10.;
+                int    num_extra   = std::max(0, (int)std::ceil(extra_depth / sp2.layer_height));
+                if (num_extra > 0) {
+                    std::vector<coordf_t> belt_layers;
+                    belt_layers.reserve(num_extra);
+                    for (int i = num_extra; i >= 1; --i)
+                        belt_layers.push_back(sp2.first_object_layer_height - i * sp2.layer_height);
+                    m_raft_layers.insert(m_raft_layers.begin(), belt_layers.begin(), belt_layers.end());
+                }
+            }
+        }
        m_current_outline_idx = 0;

        m_layer_outlines.emplace_back(mesh_settings, std::vector<Polygons>{});
@@ -114,6 +159,27 @@ TreeModelVolumes::TreeModelVolumes(
            for (size_t layer_idx = range.begin(); layer_idx < range.end(); ++ layer_idx)
                outlines[layer_idx] = polygons_simplify(to_polygons(print_object.get_layer(layer_idx - num_raft_layers)->lslices), mesh_settings.resolution, polygons_strictly_simple);
        });
+
+        // Belt floor: pre-compute belt surface polygon per-layer for clipping.
+        // Branches grow toward the belt and their slices are clipped at the belt
+        // surface in organic_draw_branches().  The organic pipeline works in LOCAL
+        // Z (no global_z_offset), so use local z_shift and local print_z.
+        {
+            const auto &slicing_params = print_object.slicing_parameters();
+            const auto &pcfg2 = print_object.print()->config();
+            BeltFloorContext ctx;
+            ctx.init_local(slicing_params, pcfg2, print_object.belt_global_z_offset());
+            if (ctx.is_active()
+                && pcfg2.belt_support_floor_mode.value == BeltSupportFloorMode::GeneratorOnly) {
+                m_belt_floor = ctx.compute_per_layer_floors(num_layers, [&](size_t layer_idx) -> double {
+                    // Use local print_z (subtract global offset from object layer).
+                    return (layer_idx >= num_raft_layers)
+                        ? print_object.get_layer(layer_idx - num_raft_layers)->print_z
+                          - print_object.belt_global_z_offset()
+                        : 0.;
+                });
+            }
+        }
    }
 #endif

@@ -469,9 +535,9 @@ void TreeModelVolumes::calculateCollision(const coord_t radius, const LayerIndex
            });

            // 2) Sum over top / bottom ranges.
-            const bool processing_last_mesh = outline_idx == layer_outline_indices.size();
+            const bool processing_last_mesh = outline_idx == layer_outline_indices.back();
            tbb::parallel_for(tbb::blocked_range<LayerIndex>(data.begin(), data.end()),
-                [&collision_areas_offsetted, &outlines, &machine_border = m_machine_border, &anti_overhang = m_anti_overhang, radius, 
+                [&collision_areas_offsetted, &outlines, &machine_border = m_machine_border, &anti_overhang = m_anti_overhang, radius,
                    xy_distance, z_distance_bottom_layers, z_distance_top_layers, min_resolution = m_min_resolution, &data, processing_last_mesh, &throw_on_cancel]
                (const tbb::blocked_range<LayerIndex>& range) {
                    for (LayerIndex layer_idx = range.begin(); layer_idx != range.end(); ++ layer_idx) {
@@ -517,9 +583,14 @@ void TreeModelVolumes::calculateCollision(const coord_t radius, const LayerIndex
                                    // not support an overhang<90 degree than to risk fusing to it.
                                append(collisions, offset(union_ex(collision_areas_original), radius + required_range_x, ClipperLib::jtMiter, 1.2));
                            }
-                        collisions = processing_last_mesh && layer_idx < int(anti_overhang.size()) ? 
-                                union_(collisions, offset(union_ex(anti_overhang[layer_idx]), radius, ClipperLib::jtMiter, 1.2)) : 
-                                union_(collisions);
+                        if (processing_last_mesh) {
+                            if (layer_idx < int(anti_overhang.size()))
+                                append(collisions, offset(union_ex(anti_overhang[layer_idx]), radius, ClipperLib::jtMiter, 1.2));
+                            // NOTE: m_belt_floor is NOT added to collision here — branches
+                            // should grow toward the belt and terminate at it, not avoid it.
+                            // Belt floor clipping is done post-generation in organic_draw_branches().
+                        }
+                        collisions = union_(collisions);
                        auto &dst = data[layer_idx];
                        if (processing_last_mesh) {
                            if (! dst.empty())
@@ -168,6 +168,9 @@ public:
    }

    Polygon m_bed_area;
+    // Belt floor polygons per layer — used for post-generation clipping
+    // in organic_draw_branches(). Public so the organic pipeline can access it.
+    std::vector<Polygons> m_belt_floor;

 private:
    // Caching polygons for a range of layers.
@@ -14,6 +14,7 @@
 #include "TreeSupportCommon.hpp"
 #include "TreeSupport.hpp"
 #include "TreeSupport3D.hpp"
+#include "BeltFloorContext.hpp"
 #include <libnest2d/backends/libslic3r/geometries.hpp>
 #include <libnest2d/placers/nfpplacer.hpp>

@@ -664,6 +665,14 @@ TreeSupport::TreeSupport(PrintObject& object, const SlicingParameters &slicing_p
 }


+double TreeSupport::belt_floor_print_z(const Point &pos_slicing) const
+{
+    BeltFloorContext ctx;
+    if (!ctx.init(m_slicing_params, *m_print_config))
+        return -std::numeric_limits<double>::infinity();
+    return ctx.floor_print_z(pos_slicing);
+}
+
 #define SUPPORT_SURFACES_OFFSET_PARAMETERS ClipperLib::jtSquare, 0.
 void TreeSupport::detect_overhangs(bool check_support_necessity/* = false*/)
 {
@@ -698,6 +707,11 @@ void TreeSupport::detect_overhangs(bool check_support_necessity/* = false*/)
    double thresh_angle = config.support_threshold_angle.value > EPSILON ? config.support_threshold_angle.value + 1 : 30;
    thresh_angle = std::min(thresh_angle, 89.); // should be smaller than 90
    const double threshold_rad = Geometry::deg2rad(thresh_angle);
+    // Build plate tilt: compute per-layer XY shift for tilted gravity direction
+    const PrintConfig& print_cfg = m_object->print()->config();
+    const double tilt_x_rad = Geometry::deg2rad(print_cfg.build_plate_tilt_x.value);
+    const double tilt_y_rad = Geometry::deg2rad(print_cfg.build_plate_tilt_y.value);
+    const bool   has_tilt   = std::abs(tilt_x_rad) > EPSILON || std::abs(tilt_y_rad) > EPSILON;
    // FIXME this is a fudge constant!
    double support_tree_tip_diameter = 0.8;
    auto   enforcer_overhang_offset  = scaled<double>(support_tree_tip_diameter);
@@ -840,8 +854,19 @@ void TreeSupport::detect_overhangs(bool check_support_necessity/* = false*/)
                ExPolygons& curr_polys = layer->lslices_extrudable;
                ExPolygons& lower_polys = lower_layer->lslices_extrudable;

+                // Apply build plate tilt: shift lower layer polygons to simulate tilted gravity
+                ExPolygons shifted_lower;
+                if (has_tilt) {
+                    shifted_lower = lower_polys; // copy
+                    const double lh = lower_layer->height;
+                    Point tilt_shift(coord_t(scale_(lh * tan(tilt_y_rad))),
+                                     coord_t(scale_(lh * tan(tilt_x_rad))));
+                    translate(shifted_lower, tilt_shift);
+                }
+                const ExPolygons &effective_lower = has_tilt ? shifted_lower : lower_polys;
+
                // normal overhang
-                ExPolygons lower_layer_offseted = offset_ex(lower_polys, support_offset_scaled, SUPPORT_SURFACES_OFFSET_PARAMETERS);
+                ExPolygons lower_layer_offseted = offset_ex(effective_lower, support_offset_scaled, SUPPORT_SURFACES_OFFSET_PARAMETERS);
                overhangs_all_layers[layer_nr] = std::move(diff_ex(curr_polys, lower_layer_offseted));

                double duration{ std::chrono::duration_cast<second_>(clock_::now() - t0).count() };
@@ -1769,6 +1794,136 @@ void TreeSupport::generate()



+    // Belt floor: extend support below the object's first layer by creating
+    // additional support layers with geometry copied from the lowest content
+    // layer and clipped at the belt surface.  These layers bypass the tree
+    // algorithm entirely — they're pure geometry added after draw_circles().
+    {
+        BeltFloorContext ctx;
+        if (ctx.init(m_slicing_params, *m_print_config)
+            && m_print_config->belt_support_floor_mode.value == BeltSupportFloorMode::GeneratorOnly) {
+            const auto &sp = m_slicing_params;
+            // Find the lowest non-empty, non-brim support layer.
+            ExPolygons source_areas;
+            double source_z = 0;
+            int layers_with_content = 0;
+            for (size_t i = 0; i < m_object->support_layer_count(); ++i) {
+                SupportLayer *sl = m_object->get_support_layer(i);
+                if (sl && !sl->base_areas.empty()) {
+                    layers_with_content++;
+                    if (layers_with_content >= 2) {
+                        source_areas = sl->base_areas;
+                        source_z = sl->print_z;
+                        break;
+                    }
+                }
+            }
+            // Fallback to first content layer.
+            if (source_areas.empty()) {
+                for (size_t i = 0; i < m_object->support_layer_count(); ++i) {
+                    SupportLayer *sl = m_object->get_support_layer(i);
+                    if (sl && !sl->base_areas.empty()) {
+                        source_areas = sl->base_areas;
+                        source_z = sl->print_z;
+                        break;
+                    }
+                }
+            }
+            // ORCA-Belt calibration: a counter-rotated calibration object
+            // stands on a support wedge that lies entirely below the object's
+            // first layer, where the tree pipeline has no layers at all — so
+            // no support content can exist yet. Seed the extension directly
+            // from the floating portion of the first layer (anything more
+            // than one layer height above the belt floor). For objects whose
+            // first layer rests on the belt the floating region is empty and
+            // behavior is unchanged.
+            double first_z = m_object->support_layer_count() > 0 ? m_object->get_support_layer(0)->print_z : 0.;
+            bool   seeded  = false;
+            if (source_areas.empty() && m_object_config->enable_support.value && !m_object->layers().empty()) {
+                // The layer grid may start with an empty ghost layer just below
+                // the object (grid rounding against the belt global Z offset) —
+                // anchor the seed to the first layer that has geometry. Object
+                // layer print_z and the floor plane are both in the globally
+                // offset frame here (belt_floor_z_shift was adjusted alongside
+                // the layer Z values in PrintObject::slice()).
+                const Layer *first_layer = nullptr;
+                for (const Layer *l : m_object->layers())
+                    if (!l->lslices_extrudable.empty()) { first_layer = l; break; }
+                if (first_layer != nullptr) {
+                    ExPolygons floating = diff_ex(first_layer->lslices_extrudable,
+                                                  ctx.surface_polygon(first_layer->bottom_z() - first_layer->height));
+                    BOOST_LOG_TRIVIAL(debug) << "[BELT-CALIB] wedge seed: obj=" << m_object->model_object()->name
+                        << " bottom_z=" << first_layer->bottom_z() << " floating=" << floating.size();
+                    if (!floating.empty()) {
+                        source_areas = std::move(floating);
+                        first_z      = first_layer->bottom_z();
+                        seeded       = true;
+                    }
+                }
+            }
+            if (!source_areas.empty()) {
+                BoundingBoxf3 bb = belt_remapped_bbox(*m_object->model_object(), m_object->print()->config());
+                double from_extent = std::abs(bb.min(ctx.from_axis()));
+                double bb_min_z    = std::abs(bb.min.z());
+                // Depth = from-axis extent + pre-shear bbox Z offset (ensure_on_bed
+                // distance) + 10mm safety margin.  The 10mm is a bodge to avoid
+                // small cutoff artifacts — ideally computed exactly from belt geometry.
+                double extra_depth = std::min(from_extent + bb_min_z + 10., std::max(0., first_z));
+                if (seeded) {
+                    // Seeded wedge: the depth is known exactly — down to the lowest
+                    // belt-floor point under the floating footprint. The bbox
+                    // heuristic above under-estimates it for meshes centered
+                    // around their origin (every object loaded through the GUI).
+                    double min_floor = first_z;
+                    for (const ExPolygon &ep : source_areas)
+                        for (const Point &pt : ep.contour.points)
+                            min_floor = std::min(min_floor, ctx.floor_print_z(pt));
+                    extra_depth = std::min(std::max(0., first_z), first_z - min_floor + 2.);
+                }
+                int num_extra = std::max(0, (int)std::ceil(extra_depth / sp.layer_height));
+                // Seeded wedge: top layers become a dense support interface so the
+                // object's floating first layer bridges a roof, not sparse infill.
+                const int interface_layers = seeded ? std::max(0, m_object_config->support_interface_top_layers.value) : 0;
+                ExPolygons prev_areas = source_areas;
+                // Build belt extension layers (lowest Z first).
+                SupportLayerPtrs belt_ext_layers;
+                for (int i = num_extra; i >= 1 && !prev_areas.empty(); --i) {
+                    double print_z = first_z - i * sp.layer_height;
+                    if (print_z < -sp.layer_height) continue;
+                    Polygons belt_surface = ctx.surface_polygon(print_z);
+                    ExPolygons clipped = diff_ex(source_areas, belt_surface);
+                    if (clipped.empty()) continue;
+                    SupportLayer *sl = new SupportLayer(0, 0, m_object, sp.layer_height, print_z, -1);
+                    sl->base_areas = clipped;
+                    // Populate area_groups — generate_toolpaths() iterates these,
+                    // not base_areas directly.
+                    // Note: base areas only get infill when support_base_pattern
+                    // is explicitly set (with the default pattern tree bases are
+                    // walls-only) — the calibration flow sets rectilinear.
+                    const bool roof = i <= interface_layers;
+                    for (auto &expoly : sl->base_areas) {
+                        sl->area_groups.emplace_back(&expoly, roof ? SupportLayer::RoofType : SupportLayer::BaseType, 0);
+                        if (roof)
+                            sl->area_groups.back().interface_id = i & 1;
+                    }
+                    sl->lslices = clipped;
+                    sl->lslices_bboxes.reserve(clipped.size());
+                    for (const ExPolygon &ep : clipped)
+                        sl->lslices_bboxes.emplace_back(get_extents(ep));
+                    belt_ext_layers.push_back(sl);
+                }
+                // Insert at the front of support_layers (they're already in Z order).
+                if (!belt_ext_layers.empty()) {
+                    auto &sl_vec = m_object->support_layers();
+                    sl_vec.insert(sl_vec.begin(), belt_ext_layers.begin(), belt_ext_layers.end());
+                    BOOST_LOG_TRIVIAL(debug) << "[BELT-CALIB] wedge ext layers=" << belt_ext_layers.size()
+                        << " z=" << belt_ext_layers.front()->print_z << ".." << belt_ext_layers.back()->print_z
+                        << " seeded=" << seeded;
+                }
+            }
+        }
+    }
+
    profiler.stage_start(STAGE_GENERATE_TOOLPATHS);
    m_object->print()->set_status(70, _u8L("Generating support"));
    generate_toolpaths();
@@ -2196,6 +2351,23 @@ void TreeSupport::draw_circles()
                base_areas = diff_ex(base_areas, ClipperUtils::clip_clipper_polygons_with_subject_bbox(roofs, get_extents(base_areas)));
                base_areas = intersection_ex(base_areas, m_machine_border);

+                // Belt floor: clip tree support polygons by the belt surface plane.
+                // ts_layer->print_z is at LOCAL Z (global offset applied later in
+                // _generate_support_material), so use init_local to subtract
+                // belt_global_z_offset from z_shift.
+                {
+                    BeltFloorContext ctx;
+                    if (ctx.init_local(m_slicing_params, *m_print_config, m_object->belt_global_z_offset())
+                        && m_print_config->belt_support_floor_mode.value == BeltSupportFloorMode::GeneratorOnly) {
+                        Polygons belt_surface = ctx.surface_polygon(ts_layer->print_z);
+                        base_areas     = diff_ex(base_areas,     belt_surface);
+                        roof_areas     = diff_ex(roof_areas,     belt_surface);
+                        roof_1st_layer = diff_ex(roof_1st_layer, belt_surface);
+                        floor_areas    = diff_ex(floor_areas,    belt_surface);
+                        roof_gap_areas = diff_ex(roof_gap_areas, belt_surface);
+                    }
+                }
+
                if (SQUARE_SUPPORT) {
                    // simplify support contours
                    ExPolygons base_areas_simplified;
@@ -2662,6 +2834,10 @@ void TreeSupport::drop_nodes()
    const size_t tip_layers = base_radius / layer_height; //The number of layers to be shrinking the circle to create a tip. This produces a 45 degree angle.
    const coordf_t radius_sample_resolution = m_ts_data->m_radius_sample_resolution;
    const bool support_on_buildplate_only = config.support_on_build_plate_only.value;
+    const size_t top_interface_layers = config.support_interface_top_layers.value;
+    const auto belt_floor_mode = m_print_config->belt_support_floor_mode.value;
+    const bool has_belt_floor = std::abs(m_slicing_params.belt_floor_shear_factor) > EPSILON
+        && belt_floor_mode == BeltSupportFloorMode::GeneratorOnly;
    const size_t bottom_interface_layers = number_of_support_interface_bottom_layers(config);
    SupportNode::diameter_angle_scale_factor = diameter_angle_scale_factor;
    float        DO_NOT_MOVER_UNDER_MM       = is_slim ? 0 : 5;                     // do not move contact points under 5mm
@@ -2895,16 +3071,23 @@ void TreeSupport::drop_nodes()
                        node_parent = p_node->parent ? p_node : neighbour;
                    // Make sure the next pass doesn't drop down either of these (since that already happened).
                    node_parent->merged_neighbours.push_front(node_parent == p_node ? neighbour : p_node);
-                    const bool to_buildplate = !is_inside_ex(get_collision(0, obj_layer_nr_next), next_position);
-                    SupportNode* next_node = m_ts_data->create_node(next_position, node_parent->distance_to_top + 1, obj_layer_nr_next,
-                        node_parent->support_roof_layers_below - (node_parent->distance_to_top > 0 ? 1 : 0),
-                        to_buildplate, node_parent, print_z_next, height_next);
-                    get_max_move_dist(next_node);
-                    m_ts_data->m_mutex.lock();
-                    contact_nodes[layer_nr_next].push_back(next_node);
+                    // Belt floor: don't drop merged node below belt surface.
+                    // Treat as object-surface termination (not buildplate) so
+                    // the node gets floor/interface areas instead of base pads.
+                    if (has_belt_floor && print_z_next <= belt_floor_print_z(next_position)) {
+                        node_parent->to_buildplate = false;
+                    } else {
+                        const bool to_buildplate = !is_inside_ex(get_collision(0, obj_layer_nr_next), next_position);
+                        SupportNode* next_node = m_ts_data->create_node(next_position, node_parent->distance_to_top + 1, obj_layer_nr_next,
+                            node_parent->support_roof_layers_below - (node_parent->distance_to_top > 0 ? 1 : 0),
+                            to_buildplate, node_parent, print_z_next, height_next);
+                        get_max_move_dist(next_node);
+                        m_ts_data->m_mutex.lock();
+                        contact_nodes[layer_nr_next].push_back(next_node);
+                        m_ts_data->m_mutex.unlock();
+                    }
                    neighbour->valid = false;
                    p_node->valid = false;
-                    m_ts_data->m_mutex.unlock();
                }
                else if (neighbours.size() > 1) //Don't merge leaf nodes because we would then incur movement greater than the maximum move distance.
                {
@@ -2948,6 +3131,12 @@ void TreeSupport::drop_nodes()
                    ExPolygons overhangs_next = diff_clipped({ node.overhang }, get_collision(0, obj_layer_nr_next));
                    for(auto& overhang:overhangs_next) {
                        Point        next_pt     = overhang.contour.centroid();
+                        // Belt floor: don't drop polygon node below belt surface.
+                        // Treat as object-surface termination (not buildplate).
+                        if (has_belt_floor && print_z_next <= belt_floor_print_z(next_pt)) {
+                            p_node->to_buildplate = false;
+                            continue;
+                        }
                        SupportNode *next_node   = m_ts_data->create_node(next_pt, p_node->distance_to_top + 1, obj_layer_nr_next,
                                                                          p_node->support_roof_layers_below - (p_node->distance_to_top > 0 ? 1 : 0),
                                                                          to_buildplate, p_node, print_z_next, height_next);
@@ -3093,6 +3282,12 @@ void TreeSupport::drop_nodes()
                        if (is_outside) { next_layer_vertex = candidate_vertex; }
                    }
                }
+                // Belt floor: don't drop regular node below belt surface.
+                // Treat as object-surface termination (not buildplate).
+                if (has_belt_floor && print_z_next <= belt_floor_print_z(next_layer_vertex)) {
+                    p_node->to_buildplate = false;
+                    return; // from parallel_for_each lambda
+                }
                auto              next_collision = get_collision(0, obj_layer_nr_next);
                const bool   to_buildplate  = !is_inside_ex(m_ts_data->m_layer_outlines[obj_layer_nr_next], next_layer_vertex);
                SupportNode *     next_node     = m_ts_data->create_node(next_layer_vertex, node.distance_to_top + 1, obj_layer_nr_next,
@@ -3406,6 +3601,10 @@ void TreeSupport::generate_contact_points()
    const coordf_t max_bridge_length = scale_(config.max_bridge_length.value);
    coord_t    radius_scaled         = scale_(base_radius);
    bool       on_buildplate_only    = m_object_config->support_on_build_plate_only.value;
+    const auto belt_floor_mode = m_print_config->belt_support_floor_mode.value;
+    const bool has_belt_floor = std::abs(m_slicing_params.belt_floor_shear_factor) > EPSILON
+        && belt_floor_mode == BeltSupportFloorMode::GeneratorOnly;
+
    //First generate grid points to cover the entire area of the print.
    BoundingBox bounding_box = m_object->bounding_box();
    const Point bounding_box_size = bounding_box.max - bounding_box.min;
@@ -3493,6 +3692,10 @@ void TreeSupport::generate_contact_points()


            auto insert_point = [&](Point pt, const ExPolygon& overhang, double radius, bool force_add = false, bool add_interface=true) {
+                // Belt floor: skip contact points whose bottom_z is at or below
+                // the belt floor at this XY position (overhang rests on the belt).
+                if (has_belt_floor && bottom_z <= belt_floor_print_z(pt))
+                    return (SupportNode*) nullptr;
                Point        hash_pos = pt / ((radius_scaled + 1) / 1);
                SupportNode* contact_node = nullptr;
                if (force_add || !already_inserted.count(hash_pos)) {
@@ -3528,8 +3731,10 @@ void TreeSupport::generate_contact_points()
                            double       radius          = unscale_(overhang_bounds.radius());
                            Point        candidate       = overhang_bounds.center();
                            SupportNode *contact_node    = insert_point(candidate, overhang, radius, true, true);
-                            contact_node->type           = ePolygon;
-                            curr_nodes.emplace_back(contact_node);
+                            if (contact_node) {
+                                contact_node->type           = ePolygon;
+                                curr_nodes.emplace_back(contact_node);
+                            }
                        }
                    }else{
                        // otherwise, all nodes should be circle nodes
@@ -3663,6 +3868,20 @@ TreeSupportData::TreeSupportData(const PrintObject &object, coordf_t xy_distance
            poly.simplify(scale_(m_radius_sample_resolution), &outline);
        }

+        // Belt floor: add belt surface polygon to layer outlines so the
+        // collision system treats the belt as a physical surface.
+        {
+            BeltFloorContext ctx;
+            double local_print_z = layer->print_z - object.belt_global_z_offset();
+            if (ctx.init_local(object.slicing_parameters(), object.print()->config(),
+                               object.belt_global_z_offset())
+                && object.print()->config().belt_support_floor_mode.value == BeltSupportFloorMode::GeneratorOnly) {
+                Polygons belt_surface = ctx.surface_polygon(local_print_z);
+                for (auto &p : belt_surface)
+                    outline.emplace_back(ExPolygon(p));
+            }
+        }
+
        if (layer_nr == 0)
            m_layer_outlines_below.push_back(outline);
        else
@@ -446,6 +446,10 @@ private:
    bool  is_slim                            = false;
    bool  with_infill                        = false;

+    // Belt printer: compute the belt floor print_z at a given XY position (in slicing coords).
+    // Returns -infinity if belt floor is not active.
+    double belt_floor_print_z(const Point &pos_slicing) const;
+


    /*!
@@ -19,6 +19,7 @@
 #include "Polygon.hpp"
 #include "Polyline.hpp"
 #include "MutablePolygon.hpp"
+#include "BeltFloorContext.hpp"
 #include "SupportCommon.hpp"
 #include "TriangleMeshSlicer.hpp"
 #include "TreeSupport.hpp"
@@ -209,6 +210,10 @@ static std::vector<std::pair<TreeSupportSettings, std::vector<size_t>>> group_me
    const bool               support_threshold_auto = support_threshold == 0;
    // +1 makes the threshold inclusive
    double                   tan_threshold          = support_threshold_auto ? 0. : tan(M_PI * double(support_threshold + 1) / 180.);
+    // Build plate tilt: compute per-layer XY shift for tilted gravity direction
+    const double             tilt_x_rad             = Geometry::deg2rad(print_config.build_plate_tilt_x.value);
+    const double             tilt_y_rad             = Geometry::deg2rad(print_config.build_plate_tilt_y.value);
+    const bool               has_tilt               = std::abs(tilt_x_rad) > EPSILON || std::abs(tilt_y_rad) > EPSILON;
    //FIXME this is a fudge constant!
    auto                     enforcer_overhang_offset = scaled<double>(config.tree_support_tip_diameter.value);
    const coordf_t radius_sample_resolution = g_config_tree_support_collision_resolution;
@@ -230,7 +235,7 @@ static std::vector<std::pair<TreeSupportSettings, std::vector<size_t>>> group_me
    size_t num_overhang_layers = support_auto ? num_object_layers : std::min(num_object_layers, std::max(size_t(support_enforce_layers), enforcers_layers.size()));
    tbb::parallel_for(tbb::blocked_range<LayerIndex>(1, num_overhang_layers),
        [&print_object, &config, &print_config, &enforcers_layers, &blockers_layers,
-         support_auto, support_enforce_layers, support_threshold_auto, tan_threshold, enforcer_overhang_offset, num_raft_layers, radius_sample_resolution, &throw_on_cancel, &out]
+         support_auto, support_enforce_layers, support_threshold_auto, tan_threshold, enforcer_overhang_offset, num_raft_layers, radius_sample_resolution, has_tilt, tilt_x_rad, tilt_y_rad, &throw_on_cancel, &out]
        (const tbb::blocked_range<LayerIndex> &range) {
        for (LayerIndex layer_id = range.begin(); layer_id < range.end(); ++ layer_id) {
            const Layer   &current_layer  = *print_object.get_layer(layer_id);
@@ -254,7 +259,15 @@ static std::vector<std::pair<TreeSupportSettings, std::vector<size_t>>> group_me
                    lower_layer_offset = external_perimeter_width - float(scale_(config.support_threshold_overlap.get_abs_value(unscale_(external_perimeter_width))));
                } else
                    lower_layer_offset = scaled<float>(lower_layer.height / tan_threshold);
-                Polygons lower_layer_offseted = offset(lower_layer.lslices_extrudable, lower_layer_offset);
+                // Apply build plate tilt: shift lower layer polygons to simulate tilted gravity
+                Polygons lower_src = to_polygons(lower_layer.lslices_extrudable);
+                if (has_tilt) {
+                    const double lh = lower_layer.height;
+                    Point tilt_shift(coord_t(scale_(lh * tan(tilt_y_rad))),
+                                     coord_t(scale_(lh * tan(tilt_x_rad))));
+                    translate(lower_src, tilt_shift);
+                }
+                Polygons lower_layer_offseted = offset(lower_src, lower_layer_offset);
                overhangs = diff(current_layer.lslices_extrudable, lower_layer_offseted);
                if (lower_layer_offset == 0) {
                    raw_overhangs = overhangs;
@@ -3418,6 +3431,37 @@ static void generate_support_areas(Print &print, TreeSupport* tree_support, cons
        // this struct is used to easy retrieve setting. No other function except those in TreeModelVolumes and generate_initial_areas() have knowledge of the existence of multiple meshes being processed.
        //FIXME this is a copy
        // Contains config settings to avoid loading them in every function. This was done to improve readability of the code.
+        // Belt printer: add virtual "belt raft" layers below the object so
+        // organic branches can extend below the model's first layer and
+        // terminate at the belt surface instead of creating a flat base at Z=0.
+        {
+            PrintObject &po = *print.get_object(processing.second.front());
+            const auto &sp  = po.slicing_parameters();
+            const auto &pcfg = po.print()->config();
+            BeltFloorContext ctx;
+            ctx.init_local(sp, pcfg, po.belt_global_z_offset());
+            if (ctx.is_active() && std::abs(po.belt_global_z_offset()) > EPSILON
+                && pcfg.belt_support_floor_mode.value == BeltSupportFloorMode::GeneratorOnly) {
+                // z_shift_local is the belt surface height at Y=0 in local coords.
+                // Extend below the belt so the base expansion and build-plate
+                // termination happen inside the belt region and get clipped.
+                // Use the distance from the pre-shear bbox min Z to the part's
+                // post-shear min Z, plus 10mm for base expansion headroom.
+                double bb_min_z    = std::abs(belt_remapped_bbox(*po.model_object(), pcfg).min.z());
+                double extra_depth = bb_min_z + 10.;
+                int    num_extra     = std::max(0, (int)std::ceil(extra_depth / sp.layer_height));
+                if (num_extra > 0) {
+                    // Insert belt raft layers at the front, from lowest Z to highest.
+                    std::vector<coordf_t> belt_layers;
+                    belt_layers.reserve(num_extra);
+                    for (int i = num_extra; i >= 1; --i)
+                        belt_layers.push_back(sp.first_object_layer_height - i * sp.layer_height);
+                    // Prepend to existing raft_layers (if any).
+                    auto &rl = processing.first.raft_layers;
+                    rl.insert(rl.begin(), belt_layers.begin(), belt_layers.end());
+                }
+            }
+        }
        const TreeSupportSettings &config = processing.first;
        BOOST_LOG_TRIVIAL(info) << "Processing support tree mesh group " << counter + 1 << " of " << grouped_meshes.size() << " containing " << grouped_meshes[counter].second.size() << " meshes.";
        auto t_start = std::chrono::high_resolution_clock::now();
@@ -3601,6 +3645,27 @@ static void generate_support_areas(Print &print, TreeSupport* tree_support, cons
            if (layer) layer->polygons = intersection(layer->polygons, volumes.m_bed_area);
        });

+        // Belt floor: clip ALL organic support layers (including intermediate/base
+        // fill) against the belt surface.  The branch slices were already clipped
+        // in organic_draw_branches(), but intermediate layers generated between
+        // branches and the build plate need clipping too.
+        // Compute the belt floor polygon directly from each layer's print_z
+        // rather than mapping to a layer index (avoids index mismatch issues).
+        {
+            const auto &sp   = print_object.slicing_parameters();
+            const auto &pcfg = print_object.print()->config();
+            BeltFloorContext ctx;
+            ctx.init_local(sp, pcfg, print_object.belt_global_z_offset());
+            if (ctx.is_active()
+                && pcfg.belt_support_floor_mode.value == BeltSupportFloorMode::GeneratorOnly) {
+                tbb::parallel_for_each(layers_sorted.begin(), layers_sorted.end(), [&](SupportGeneratorLayer *layer) {
+                    if (!layer || layer->polygons.empty())
+                        return;
+                    layer->polygons = diff(layer->polygons, ctx.surface_polygon(layer->print_z));
+                });
+            }
+        }
+
        print.set_status(69, _L("Generating support"));
        generate_support_toolpaths(print_object.support_layers(), print_object.config(), support_params, print_object.slicing_parameters(),
            raft_layers, bottom_contacts, top_contacts, intermediate_layers, interface_layers, base_interface_layers);
@@ -3891,6 +3956,10 @@ void organic_draw_branches(
                        // ORCA: safety offset when trimming collision/bed to improve robustness.
                        slices[i] = diff_clipped(slices[i], volumes.getCollision(0, layer_begin + i, true), ApplySafetyOffset::Yes); // FIXME parent_uses_min || draw_area.element->state.use_min_xy_dist);
                        slices[i] = intersection(slices[i], volumes.m_bed_area, ApplySafetyOffset::Yes);
+                        // Belt floor: clip branch slices against the belt surface plane.
+                        LayerIndex belt_idx = layer_begin + i;
+                        if (belt_idx < LayerIndex(volumes.m_belt_floor.size()) && !volumes.m_belt_floor[belt_idx].empty())
+                            slices[i] = diff(slices[i], volumes.m_belt_floor[belt_idx]);
                        remove_small(slices[i], tiny_area);
                    }

@@ -3935,7 +4004,10 @@ void organic_draw_branches(
                                if (!contacts.empty())
                                    bottom_contacts.emplace_back(std::move(contacts));
                            }
-                        } else if (layer_begin > 0) {
+                        } else if (layer_begin > 0 && (volumes.m_belt_floor.empty() || num_empty == 0)) {
+                            // Belt-floor clipping makes initial slices empty often; without this
+                            // gate, "verylost" branches propagate rest_support down to layer 0 and
+                            // OOM on tall belt prints.
                            // Drop down areas that do rest non - gracefully on the model to ensure the branch actually rests on something.
                            struct BottomExtraSlice {
                                Polygons polygons;
@@ -3960,6 +4032,9 @@ void organic_draw_branches(
                                LayerIndex collision_layer = (layer_idx == layer_begin - 1) ? layer_begin : layer_idx;
                                Polygons collision = volumes.getCollision(0, collision_layer, false);
                                rest_support = diff_clipped(rest_support.empty() ? slice_front_contact : rest_support, collision, ApplySafetyOffset::Yes);
+                                // Belt floor: clip propagated support at belt surface.
+                                if (layer_idx < LayerIndex(volumes.m_belt_floor.size()) && !volumes.m_belt_floor[layer_idx].empty())
+                                    rest_support = diff(rest_support, volumes.m_belt_floor[layer_idx]);
                                remove_small(rest_support, tiny_area);
                                double rest_support_area = area(rest_support);
                                if (rest_support_area < support_area_stop)
@@ -280,7 +280,7 @@ int TriangleSelector::select_unsplit_triangle(const Vec3f &hit, int facet_idx) c
    return this->select_unsplit_triangle(hit, facet_idx, neighbors);
 }

-void TriangleSelector::select_patch(int facet_start, std::unique_ptr<Cursor> &&cursor, EnforcerBlockerType new_state, const Transform3d& trafo_no_translate, bool triangle_splitting, float highlight_by_angle_deg, const bool select_partially)
+void TriangleSelector::select_patch(int facet_start, std::unique_ptr<Cursor> &&cursor, EnforcerBlockerType new_state, const Transform3d& trafo_no_translate, bool triangle_splitting, float highlight_by_angle_deg, const Vec3f &up_direction, const bool select_partially)
 {
    assert(facet_start < m_orig_size_indices);

@@ -341,8 +341,8 @@ void TriangleSelector::select_patch(int facet_start, std::unique_ptr<Cursor> &&c
            int          facet = facets_to_check[facet_idx];
            const Vec3f& facet_normal = m_face_normals[m_triangles[facet].source_triangle];
            Matrix3f     normal_matrix = static_cast<Matrix3f>(trafo_no_translate.matrix().block(0, 0, 3, 3).inverse().transpose().cast<float>());
-            float        world_normal_z = (normal_matrix* facet_normal).normalized().z();
-            if (!visited[facet] && (highlight_by_angle_deg == 0.f || world_normal_z < highlight_angle_limit)) {
+            float        world_normal_dot = (normal_matrix * facet_normal).normalized().dot(up_direction);
+            if (!visited[facet] && (highlight_by_angle_deg == 0.f || world_normal_dot < highlight_angle_limit)) {
                if (select_triangle(facet, new_state, triangle_splitting, select_partially)) {
                    // add neighboring facets to list to be processed later
                    for (int neighbor_idx : m_neighbors[facet])
@@ -367,7 +367,7 @@ bool TriangleSelector::is_facet_clipped(int facet_idx, const ClippingPlane &clp)

 void TriangleSelector::seed_fill_select_triangles(const Vec3f &hit, int facet_start, const Transform3d& trafo_no_translate,
                                                  const ClippingPlane &clp, float seed_fill_angle, float highlight_by_angle_deg,
-                                                  bool force_reselection)
+                                                  bool force_reselection, const Vec3f &up_direction)
 {
    assert(facet_start < m_orig_size_indices);

@@ -391,8 +391,8 @@ void TriangleSelector::seed_fill_select_triangles(const Vec3f &hit, int facet_st

        const Vec3f &facet_normal = m_face_normals[m_triangles[current_facet].source_triangle];
        Matrix3f     normal_matrix  = static_cast<Matrix3f>(trafo_no_translate.matrix().block(0, 0, 3, 3).inverse().transpose().cast<float>());
-        float        world_normal_z = (normal_matrix * facet_normal).normalized().z();
-        if (!visited[current_facet] && (highlight_by_angle_deg == 0.f || world_normal_z < highlight_angle_limit)) {
+        float        world_normal_dot = (normal_matrix * facet_normal).normalized().dot(up_direction);
+        if (!visited[current_facet] && (highlight_by_angle_deg == 0.f || world_normal_dot < highlight_angle_limit)) {
            if (m_triangles[current_facet].is_split()) {
                for (int split_triangle_idx = 0; split_triangle_idx <= m_triangles[current_facet].number_of_split_sides(); ++split_triangle_idx) {
                    assert(split_triangle_idx < int(m_triangles[current_facet].children.size()));
@@ -2515,7 +2515,7 @@ TriangleSelector::TriangleSplittingData TriangleSelector::remap_painting(
            if (TriangleCursor::check_normal(norm_b, -norm_a) && check_overlap(pv0, pv1, pv2, ta, tb, tc)) {
                // Paint this face
                target_selector.select_patch(face_idx, TriangleCursor::build_cursor(source_selector, tri), tri.get_state(),
-                                             Transform3d::Identity(), true, 0.f, true);
+                                             Transform3d::Identity(), true, 0.f, Vec3f::UnitZ(), true);
            }
            return true; // continue traversal
        });
@@ -309,6 +309,7 @@ public:
                      const Transform3d        &trafo_no_translate,            // matrix to get from mesh to world without translation
                      bool                      triangle_splitting,            // If triangles will be split base on the cursor or not
                      float                     highlight_by_angle_deg = 0.f,  // The maximal angle of overhang. If it is set to a non-zero value, it is possible to paint only the triangles of overhang defined by this angle in degrees.
+                      const Vec3f              &up_direction = Vec3f::UnitZ(), // Up direction for overhang detection (accounts for build plate tilt)
                      bool                      select_partially = false);     // Select a triangle if it's partially in the cursor but too small to be subdivided

    void seed_fill_select_triangles(const Vec3f        &hit,                          // point where to start
@@ -317,7 +318,8 @@ public:
                                    const ClippingPlane &clp,                         // Clipping plane to limit painting to not clipped facets only
                                    float               seed_fill_angle,              // the maximal angle between two facets to be painted by the same color
                                    float               highlight_by_angle_deg = 0.f, // The maximal angle of overhang. If it is set to a non-zero value, it is possible to paint only the triangles of overhang defined by this angle in degrees.
-                                    bool                force_reselection = false);   // force reselection of the triangle mesh even in cases that mouse is pointing on the selected triangle
+                                    bool                force_reselection = false,    // force reselection of the triangle mesh even in cases that mouse is pointing on the selected triangle
+                                    const Vec3f        &up_direction = Vec3f::UnitZ()); // Up direction for overhang detection (accounts for build plate tilt)

    void bucket_fill_select_triangles(const Vec3f         &hit,                        // point where to start
                                      int                  facet_start,                // facet of the original mesh (unsplit) that the hit point belongs to
@@ -1,4 +1,5 @@
 #include "calib.hpp"
+#include "BeltGCodeWriter.hpp"
 #include "BoundingBox.hpp"
 #include "Config.hpp"
 #include "Model.hpp"
@@ -587,21 +588,21 @@ CustomGCode::Info CalibPressureAdvancePattern::generate_custom_gcodes(const Dyna

        refresh_setup(config, is_bbl_machine, object, origin);

-    gcode << move_to(Vec2d(m_starting_point.x(), m_starting_point.y()), m_writer, "Move to start XY position");
-    gcode << m_writer.travel_to_z(height_first_layer() + height_z_offset(), "Move to start Z position");
-    gcode << m_writer.set_pressure_advance(m_params.start);
+    gcode << move_to(Vec2d(m_starting_point.x(), m_starting_point.y()), *m_writer, "Move to start XY position");
+    gcode << m_writer->travel_to_z(height_first_layer() + height_z_offset(), "Move to start Z position");
+    gcode << m_writer->set_pressure_advance(m_params.start);

    const DrawBoxOptArgs default_box_opt_args(wall_count(), height_first_layer(), line_width_first_layer(),
                                              speed_adjust(speed_first_layer()));

    // create anchoring frame
-    gcode << draw_box(m_writer, m_starting_point.x(), m_starting_point.y(), print_size_x(), frame_size_y(), default_box_opt_args);
+    gcode << draw_box(*m_writer, m_starting_point.x(), m_starting_point.y(), print_size_x(), frame_size_y(), default_box_opt_args);

    // create tab for numbers
    DrawBoxOptArgs draw_box_opt_args = default_box_opt_args;
    draw_box_opt_args.is_filled      = true;
    draw_box_opt_args.num_perimeters = wall_count();
-    gcode << draw_box(m_writer, m_starting_point.x(), m_starting_point.y() + frame_size_y() + line_spacing_first_layer(),
+    gcode << draw_box(*m_writer, m_starting_point.x(), m_starting_point.y() + frame_size_y() + line_spacing_first_layer(),
                      print_size_x(),
                      max_numbering_height() + line_spacing_first_layer() + m_glyph_padding_vertical * 2, draw_box_opt_args);

@@ -627,15 +628,15 @@ CustomGCode::Info CalibPressureAdvancePattern::generate_custom_gcodes(const Dyna
            gcode = std::stringstream(); // reset for next layer contents
            gcode << "; start pressure advance pattern for layer\n";

-            gcode << m_writer.travel_to_z(layer_height, "Move to layer height");
-            gcode << m_writer.reset_e();
+            gcode << m_writer->travel_to_z(layer_height, "Move to layer height");
+            gcode << m_writer->reset_e();
        }

        // line numbering
        if (i == 1) {
            m_number_len = max_numbering_length();

-            gcode << m_writer.set_pressure_advance(m_params.start);
+            gcode << m_writer->set_pressure_advance(m_params.start);

            double number_e_per_mm = e_per_mm(line_width(), height_layer(),
                                              m_config.option<ConfigOptionFloats>("nozzle_diameter")->get_at(0),
@@ -646,20 +647,20 @@ CustomGCode::Info CalibPressureAdvancePattern::generate_custom_gcodes(const Dyna
            for (int j = 0; j < num_patterns; j += 2) {
                gcode << draw_number(glyph_start_x(j), m_starting_point.y() + frame_size_y() + m_glyph_padding_vertical + line_width(),
                                     m_params.start + (j * m_params.step), m_draw_digit_mode, line_width(), number_e_per_mm,
-                                     speed_first_layer(), m_writer);
+                                     speed_first_layer(), *m_writer);
            }

            // flow value
            int line_num = num_patterns + 2;
            gcode << draw_number(glyph_start_x(line_num), m_starting_point.y() + frame_size_y() + m_glyph_padding_vertical + line_width(),
                                 flow_val(), m_draw_digit_mode, line_width(), number_e_per_mm,
-                                 speed_first_layer(), m_writer);
+                                 speed_first_layer(), *m_writer);

            // acceleration
            line_num = num_patterns + 4;
            gcode << draw_number(glyph_start_x(line_num), m_starting_point.y() + frame_size_y() + m_glyph_padding_vertical + line_width(),
                                 accel, m_draw_digit_mode, line_width(), number_e_per_mm,
-                                 speed_first_layer(), m_writer);
+                                 speed_first_layer(), *m_writer);
        }


@@ -678,20 +679,20 @@ CustomGCode::Info CalibPressureAdvancePattern::generate_custom_gcodes(const Dyna
            /* Draw a line at slightly slower accel and speed in order to trick gcode writer to force update acceleration and speed.
             * We do this since several tests may be generated by their own gcode writers which are
             * not aware about their neighbours updating acceleration/speed */
-            gcode << m_writer.set_print_acceleration(std::max<int>(1, accel - 1));
-            gcode << move_to(Vec2d(m_starting_point.x(), m_starting_point.y()), m_writer, "Move to starting point", zhop_height, layer_height);
-            gcode << draw_line(m_writer, Vec2d(m_starting_point.x(), m_starting_point.y() + frame_size_y()), line_width(), height_layer(), speed_adjust(std::max<int>(1, speed_perimeter() - 1)), "Accel/flow trick line");
-            gcode << m_writer.set_print_acceleration(accel);
+            gcode << m_writer->set_print_acceleration(std::max<int>(1, accel - 1));
+            gcode << move_to(Vec2d(m_starting_point.x(), m_starting_point.y()), *m_writer, "Move to starting point", zhop_height, layer_height);
+            gcode << draw_line(*m_writer, Vec2d(m_starting_point.x(), m_starting_point.y() + frame_size_y()), line_width(), height_layer(), speed_adjust(std::max<int>(1, speed_perimeter() - 1)), "Accel/flow trick line");
+            gcode << m_writer->set_print_acceleration(accel);
        }

        double initial_x = to_x;
        double initial_y = to_y;

-        gcode << move_to(Vec2d(to_x, to_y), m_writer, "Move to pattern start",zhop_height,layer_height);
+        gcode << move_to(Vec2d(to_x, to_y), *m_writer, "Move to pattern start",zhop_height,layer_height);

        for (int j = 0; j < num_patterns; ++j) {
            // increment pressure advance
-            gcode << m_writer.set_pressure_advance(m_params.start + (j * m_params.step));
+            gcode << m_writer->set_pressure_advance(m_params.start + (j * m_params.step));

            for (int k = 0; k < wall_count(); ++k) {
                to_x += std::cos(to_radians(m_corner_angle) / 2) * side_length;
@@ -701,27 +702,27 @@ CustomGCode::Info CalibPressureAdvancePattern::generate_custom_gcodes(const Dyna
                auto draw_line_arg_line_width = line_width(); // don't use line_width_first_layer so results are consistent across all layers
                auto draw_line_arg_speed   = i == 0 ? speed_adjust(speed_first_layer()) : speed_adjust(speed_perimeter());
                auto draw_line_arg_comment = "Print pattern wall";
-                gcode << draw_line(m_writer, Vec2d(to_x, to_y), draw_line_arg_line_width, draw_line_arg_height, draw_line_arg_speed, draw_line_arg_comment);
+                gcode << draw_line(*m_writer, Vec2d(to_x, to_y), draw_line_arg_line_width, draw_line_arg_height, draw_line_arg_speed, draw_line_arg_comment);

                to_x -= std::cos(to_radians(m_corner_angle) / 2) * side_length;
                to_y += std::sin(to_radians(m_corner_angle) / 2) * side_length;

-                gcode << draw_line(m_writer, Vec2d(to_x, to_y), draw_line_arg_line_width, draw_line_arg_height, draw_line_arg_speed, draw_line_arg_comment);
+                gcode << draw_line(*m_writer, Vec2d(to_x, to_y), draw_line_arg_line_width, draw_line_arg_height, draw_line_arg_speed, draw_line_arg_comment);

                to_y = initial_y;
                if (k != wall_count() - 1) {
                    // perimeters not done yet. move to next perimeter
                    to_x += line_spacing_angle();
-                    gcode << move_to(Vec2d(to_x, to_y), m_writer, "Move to start next pattern wall", zhop_height, layer_height); // Call move to command with XY as well as z hop and layer height to invoke and undo z lift
+                    gcode << move_to(Vec2d(to_x, to_y), *m_writer, "Move to start next pattern wall", zhop_height, layer_height); // Call move to command with XY as well as z hop and layer height to invoke and undo z lift
                } else if (j != num_patterns - 1) {
                    // patterns not done yet. move to next pattern
                    to_x += m_pattern_spacing + line_width();
-                    gcode << move_to(Vec2d(to_x, to_y), m_writer, "Move to next pattern", zhop_height, layer_height); // Call move to command with XY as well as z hop and layer height to invoke and undo z lift
+                    gcode << move_to(Vec2d(to_x, to_y), *m_writer, "Move to next pattern", zhop_height, layer_height); // Call move to command with XY as well as z hop and layer height to invoke and undo z lift
                } else if (i != m_num_layers - 1) {
                    // layers not done yet. move back to start
                    to_x = initial_x;
-                    gcode << move_to(Vec2d(to_x, to_y), m_writer, "Move back to start position", zhop_height, layer_height); // Call move to command with XY as well as z hop and layer height to invoke and undo z lift
-                    gcode << m_writer.reset_e(); // reset extruder before printing placeholder cube to avoid over extrusion
+                    gcode << move_to(Vec2d(to_x, to_y), *m_writer, "Move back to start position", zhop_height, layer_height); // Call move to command with XY as well as z hop and layer height to invoke and undo z lift
+                    gcode << m_writer->reset_e(); // reset extruder before printing placeholder cube to avoid over extrusion
                } else {
                    // everything done
                }
@@ -729,7 +730,7 @@ CustomGCode::Info CalibPressureAdvancePattern::generate_custom_gcodes(const Dyna
        }
    }

-    gcode << m_writer.set_pressure_advance(m_params.start);
+    gcode << m_writer->set_pressure_advance(m_params.start);
    gcode << "; end pressure advance pattern for layer\n";

    CustomGCode::Item item;
@@ -796,13 +797,36 @@ void CalibPressureAdvancePattern::_refresh_writer(bool is_bbl_machine, const Mod
    PrintConfig print_config;
    print_config.apply(m_config, true);

-    m_writer.apply_print_config(print_config);
-    m_writer.set_xy_offset(origin(0), origin(1));
-    m_writer.set_is_bbl_machine(is_bbl_machine);
+    // ORCA-Belt: the pattern is drawn in logical bed coordinates directly on
+    // the build surface — on a belt printer that means the belt plane, which
+    // needs the machine kinematics (axis remap + frame shear/scale) with the
+    // coordinates interpreted as world points (see set_world_coordinates).
+    if (print_config.belt_printer.value) {
+        auto belt_writer = std::make_shared<BeltGCodeWriter>();
+        belt_writer->set_belt_back_transform(print_config);
+        belt_writer->set_machine_frame_transform(print_config);
+        belt_writer->set_world_coordinates(true);
+        const int rx = int(print_config.gcode_remap_x.value);
+        const int ry = int(print_config.gcode_remap_y.value);
+        const int rz = int(print_config.gcode_remap_z.value);
+        if (rx != 0 || ry != 1 || rz != 2) {
+            belt_writer->set_axis_remap(rx, ry, rz);
+            BoundingBoxf bbox_bed(print_config.printable_area.values);
+            belt_writer->set_build_volume_max(Vec3d(bbox_bed.max.x(), bbox_bed.max.y(),
+                                                    print_config.printable_height.value));
+        }
+        m_writer = std::move(belt_writer);
+    } else if (dynamic_cast<BeltGCodeWriter*>(m_writer.get()) != nullptr) {
+        m_writer = std::make_shared<GCodeWriter>();
+    }
+
+    m_writer->apply_print_config(print_config);
+    m_writer->set_xy_offset(origin(0), origin(1));
+    m_writer->set_is_bbl_machine(is_bbl_machine);

    const unsigned int extruder_id = object.volumes.front()->extruder_id();
-    m_writer.set_extruders({extruder_id});
-    m_writer.set_extruder(extruder_id);
+    m_writer->set_extruders({extruder_id});
+    m_writer->set_extruder(extruder_id);
 }

 double CalibPressureAdvancePattern::object_size_x() const
@@ -358,7 +358,10 @@ private:

    const Calib_Params &m_params;

-    GCodeWriter        m_writer;
+    // Polymorphic so belt printers get a BeltGCodeWriter in world-coordinates
+    // mode (_refresh_writer); shared_ptr keeps the class copyable — the writer
+    // is rebuilt by refresh_setup() before every use anyway.
+    std::shared_ptr<GCodeWriter> m_writer{std::make_shared<GCodeWriter>()};
    Vec3d              m_starting_point;
    bool               m_is_start_point_fixed = false;

@@ -387,6 +387,9 @@ void Bed3D::render_internal(GLCanvas3D& canvas, const Transform3d& view_matrix,

    m_model.set_color(m_is_dark ? DEFAULT_MODEL_COLOR_DARK : DEFAULT_MODEL_COLOR);

+    // Belt printer: bed rotation is applied inside render_model() and render_default()
+    // using m_is_belt_printer and m_belt_angle members.
+
    switch (m_type)
    {
    case Type::System: { render_system(canvas, view_matrix, projection_matrix, bottom); break; }
@@ -394,6 +397,10 @@ void Bed3D::render_internal(GLCanvas3D& canvas, const Transform3d& view_matrix,
    case Type::Custom: { render_custom(canvas, view_matrix, projection_matrix, bottom); break; }
    }

+    render_gravity_arrow(view_matrix, projection_matrix);
+    render_slicing_arrow(view_matrix, projection_matrix);
+    render_slicing_plane(view_matrix, projection_matrix);
+
    glsafe(::glDisable(GL_DEPTH_TEST));
 }

@@ -692,7 +699,13 @@ void Bed3D::render_model(const Transform3d& view_matrix, const Transform3d& proj
        if (shader != nullptr) {
            shader->start_using();
            shader->set_uniform("emission_factor", 0.0f);
-            const Transform3d model_matrix = Geometry::assemble_transform(m_model_offset);
+            Transform3d model_matrix = Geometry::assemble_transform(m_model_offset);
+            // Belt printer: rotate the bed model about the tilt axis so the belt tilt
+            // is visible.  Negative angle: belt surface tilts downward away from the nozzle.
+            if (m_is_belt_printer && m_belt_angle > 0.f) {
+                double angle_rad = Geometry::deg2rad(static_cast<double>(m_belt_angle));
+                model_matrix = Eigen::AngleAxisd(-angle_rad, belt_tilt_unit_axis()) * model_matrix;
+            }
            shader->set_uniform("volume_world_matrix",  model_matrix);
            shader->set_uniform("view_model_matrix", view_matrix * model_matrix);
            shader->set_uniform("projection_matrix", projection_matrix);
@@ -731,6 +744,173 @@ void Bed3D::render_custom(GLCanvas3D& canvas, const Transform3d& view_matrix, co
        render_texture(bottom, canvas);*/
 }

+void Bed3D::render_gravity_arrow(const Transform3d& view_matrix, const Transform3d& projection_matrix)
+{
+    const DynamicPrintConfig& cfg = wxGetApp().preset_bundle->printers.get_edited_preset().config;
+    // build_plate_tilt_{x,y} are kept in sync with the belt tilt (see TabPrinter), so
+    // reading them here covers both belt and non-belt tilted printers.
+    double tilt_x_deg = cfg.opt_float("build_plate_tilt_x");
+    double tilt_y_deg = cfg.opt_float("build_plate_tilt_y");
+    if (tilt_x_deg == 0. && tilt_y_deg == 0.) {
+        m_gravity_arrow.reset();
+        return;
+    }
+
+    // Gravity direction (matching the slicer's tilt convention)
+    double tilt_x_rad = Geometry::deg2rad(tilt_x_deg);
+    double tilt_y_rad = Geometry::deg2rad(tilt_y_deg);
+    Vec3d gravity_dir = Vec3d(-tan(tilt_y_rad), -tan(tilt_x_rad), -1.0).normalized();
+
+    // Build the arrow model (same dimensions as the axis arrows)
+    if (!m_gravity_arrow.is_initialized()) {
+        const float stem_length = Axes::DefaultStemLength;
+        const float tip_radius  = Axes::DefaultTipRadius;
+        const float tip_length  = Axes::DefaultTipLength;
+        const float stem_radius = stem_length / 75.f; // same ratio as axis cylinders
+        m_gravity_arrow.init_from(stilized_arrow(16, tip_radius, tip_length, stem_radius, stem_length));
+    }
+
+    // The arrow model points along +Z by default. Compute rotation to align with gravity_dir.
+    // Rotation axis = cross(+Z, gravity_dir), angle = acos(dot(+Z, gravity_dir))
+    Vec3d from = Vec3d::UnitZ();
+    Vec3d to   = gravity_dir;
+    double dot  = from.dot(to);
+    Transform3d rot = Transform3d::Identity();
+    if (dot < -0.9999) {
+        // Nearly opposite — rotate 180° around X
+        rot = Eigen::AngleAxisd(M_PI, Vec3d::UnitX()) * rot;
+    } else if (dot < 0.9999) {
+        Vec3d axis  = from.cross(to).normalized();
+        double angle = std::acos(std::clamp(dot, -1.0, 1.0));
+        rot = Eigen::AngleAxisd(angle, axis) * rot;
+    }
+
+    GLShaderProgram* shader = wxGetApp().get_shader("flat");
+    if (shader == nullptr)
+        return;
+
+    glsafe(::glEnable(GL_DEPTH_TEST));
+    shader->start_using();
+
+    const Camera& camera = wxGetApp().plater()->get_camera();
+    Transform3d model_matrix = rot;
+    shader->set_uniform("view_model_matrix", camera.get_view_matrix() * model_matrix);
+    shader->set_uniform("projection_matrix", camera.get_projection_matrix());
+
+    m_gravity_arrow.set_color({ 1.0f, 0.85f, 0.0f, 1.0f }); // yellow
+    m_gravity_arrow.render();
+
+    shader->stop_using();
+}
+
+void Bed3D::render_slicing_arrow(const Transform3d& view_matrix, const Transform3d& projection_matrix)
+{
+    if (!m_is_belt_printer || m_belt_angle <= 0.f)
+        return;
+
+    // Build the arrow model: shorter and wider than the gravity arrow.
+    if (!m_slicing_arrow.is_initialized()) {
+        const float stem_length = 15.0f;   // shorter than gravity arrow (25)
+        const float stem_radius = 1.0f;    // wider than gravity arrow (~0.33)
+        const float tip_radius  = 3.0f;    // wider tip
+        const float tip_length  = 5.0f;
+        m_slicing_arrow.init_from(stilized_arrow(16, tip_radius, tip_length, stem_radius, stem_length));
+    }
+
+    // The slicing direction: layers stack along the gantry normal, i.e. the image of
+    // +Z under the mesh rotation about the tilt axis.  Use the same AngleAxis as the
+    // slicing pipeline so the arrow matches whichever tilt axis is configured.
+    double angle_rad = Geometry::deg2rad(static_cast<double>(m_belt_angle));
+    Vec3d slice_dir = (Eigen::AngleAxisd(angle_rad, belt_tilt_unit_axis()).toRotationMatrix()
+                       * Vec3d::UnitZ()).normalized();
+
+    // Compute rotation to align +Z (arrow default) with slice_dir.
+    Vec3d from = Vec3d::UnitZ();
+    double dot = from.dot(slice_dir);
+    Transform3d rot = Transform3d::Identity();
+    if (dot < -0.9999) {
+        rot = Eigen::AngleAxisd(M_PI, Vec3d::UnitX()) * rot;
+    } else if (dot < 0.9999) {
+        Vec3d axis  = from.cross(slice_dir).normalized();
+        double angle = std::acos(std::clamp(dot, -1.0, 1.0));
+        rot = Eigen::AngleAxisd(angle, axis) * rot;
+    }
+
+    GLShaderProgram* shader = wxGetApp().get_shader("flat");
+    if (shader == nullptr)
+        return;
+
+    // Disable depth test so the arrow is always visible (not occluded by the tilted bed).
+    glsafe(::glDisable(GL_DEPTH_TEST));
+    shader->start_using();
+
+    const Camera& camera = wxGetApp().plater()->get_camera();
+    Transform3d model_matrix = rot;
+    shader->set_uniform("view_model_matrix", camera.get_view_matrix() * model_matrix);
+    shader->set_uniform("projection_matrix", camera.get_projection_matrix());
+
+    m_slicing_arrow.set_color({ 1.0f, 0.2f, 0.6f, 1.0f }); // pink
+    m_slicing_arrow.render();
+
+    shader->stop_using();
+    glsafe(::glEnable(GL_DEPTH_TEST));
+}
+
+void Bed3D::render_slicing_plane(const Transform3d& view_matrix, const Transform3d& projection_matrix)
+{
+    if (!m_is_belt_printer || m_belt_angle <= 0.f)
+        return;
+
+    // Build a quad in the XZ plane (world frame) representing the belt slicing plane.
+    // The plane is tilted at belt_angle from horizontal, with normal (0, -sin(a), cos(a)).
+    // We render it as a semi-transparent quad centered on the build plate.
+    if (!m_slicing_plane.is_initialized()) {
+        const float half_size = 120.f;  // mm, large enough to be visible
+        GLModel::Geometry init_data;
+        init_data.format = { GLModel::Geometry::EPrimitiveType::Triangles, GLModel::Geometry::EVertexLayout::P3N3 };
+        init_data.reserve_vertices(4);
+        init_data.reserve_indices(2);  // 2 triangles
+
+        // Quad corners in local frame (XY plane, will be rotated to match slicing plane)
+        Vec3f n = Vec3f::UnitZ();
+        init_data.add_vertex(Vec3f(-half_size, -half_size, 0.f), n);
+        init_data.add_vertex(Vec3f( half_size, -half_size, 0.f), n);
+        init_data.add_vertex(Vec3f( half_size,  half_size, 0.f), n);
+        init_data.add_vertex(Vec3f(-half_size,  half_size, 0.f), n);
+        init_data.add_triangle(0, 1, 2);
+        init_data.add_triangle(0, 2, 3);
+
+        m_slicing_plane.init_from(std::move(init_data));
+    }
+
+    GLShaderProgram* shader = wxGetApp().get_shader("flat");
+    if (shader == nullptr)
+        return;
+
+    glsafe(::glEnable(GL_DEPTH_TEST));
+    glsafe(::glEnable(GL_BLEND));
+    glsafe(::glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA));
+
+    shader->start_using();
+
+    // Show a tilted plane representing the slicing direction.
+    // The slicing plane is rotated by belt_angle about the tilt axis from horizontal.
+    // Raise it slightly so it's visible above the bed surface.
+    double angle_rad = Geometry::deg2rad(static_cast<double>(m_belt_angle));
+    Transform3d model_matrix = Transform3d::Identity();
+    model_matrix.translate(Vec3d(0., 0., 30.));
+    model_matrix.rotate(Eigen::AngleAxisd(angle_rad, belt_tilt_unit_axis()));
+
+    shader->set_uniform("view_model_matrix", view_matrix * model_matrix);
+    shader->set_uniform("projection_matrix", projection_matrix);
+
+    m_slicing_plane.set_color({ 0.2f, 0.6f, 1.0f, 0.3f });  // semi-transparent blue
+    m_slicing_plane.render();
+
+    glsafe(::glDisable(GL_BLEND));
+    shader->stop_using();
+}
+
 void Bed3D::render_default(bool bottom, const Transform3d& view_matrix, const Transform3d& projection_matrix)
 {
    // m_texture.reset();
@@ -741,7 +921,15 @@ void Bed3D::render_default(bool bottom, const Transform3d& view_matrix, const Tr
    if (shader != nullptr) {
        shader->start_using();

-        shader->set_uniform("view_model_matrix", view_matrix);
+        // Belt printer: rotate the default bed about X so the belt tilt is visible.
+        Transform3d view_model_matrix = view_matrix;
+        if (m_is_belt_printer && m_belt_angle > 0.f) {
+            double angle_rad = Geometry::deg2rad(static_cast<double>(m_belt_angle));
+            Transform3d belt_rotation = Transform3d::Identity();
+            belt_rotation.rotate(Eigen::AngleAxisd(-angle_rad, Vec3d::UnitX()));
+            view_model_matrix = view_matrix * belt_rotation;
+        }
+        shader->set_uniform("view_model_matrix", view_model_matrix);
        shader->set_uniform("projection_matrix", projection_matrix);

        glsafe(::glEnable(GL_DEPTH_TEST));
@@ -110,6 +110,9 @@ private:
    //GLTexture m_temp_texture;
    GLModel m_model;
    Vec3d m_model_offset{ Vec3d::Zero() };
+    GLModel m_gravity_arrow;
+    GLModel m_slicing_arrow;  // Pink arrow showing the effective slicing direction
+    GLModel m_slicing_plane;  // Debug: shows the intended slicing plane direction
    Axes m_axes;

    float m_scale_factor{ 1.0f };
@@ -119,6 +122,11 @@ private:
    std::vector<std::vector<Vec2d>> m_extruder_shapes;
    std::vector<double> m_extruder_heights;
    bool m_is_dark = false;
+    // Belt printer state for rendering.
+    bool  m_is_belt_printer = false;
+    float m_belt_angle = 0.f;
+    // Tilt axis: 0 = X (belt travels along Y, the common case), 1 = Y.
+    int   m_belt_tilt_axis = 0;

 public:
    Bed3D() = default;
@@ -138,6 +146,16 @@ public:

    // Build volume geometry for various collision detection tasks.
    const BuildVolume& build_volume() const { return m_build_volume; }
+    BuildVolume& build_volume() { return m_build_volume; }
+
+    // Belt printer bed settings.  tilt_axis: 0 = X (belt along Y), 1 = Y.
+    void set_belt_printer(bool enabled, float angle_deg, int tilt_axis = 0) {
+        m_is_belt_printer = enabled; m_belt_angle = angle_deg; m_belt_tilt_axis = tilt_axis;
+    }
+    bool is_belt_printer() const { return m_is_belt_printer; }
+    float belt_angle() const { return m_belt_angle; }
+    // Unit vector of the tilt axis in bed space.
+    Vec3d belt_tilt_unit_axis() const { return m_belt_tilt_axis == 1 ? Vec3d::UnitY() : Vec3d::UnitX(); }

    // Was the model provided, or was it generated procedurally?
    Type get_type() const { return m_type; }
@@ -177,7 +195,10 @@ private:
    void render_model(const Transform3d& view_matrix, const Transform3d& projection_matrix);
    void render_custom(GLCanvas3D& canvas, const Transform3d& view_matrix, const Transform3d& projection_matrix, bool bottom);
    void render_default(bool bottom, const Transform3d& view_matrix, const Transform3d& projection_matrix);
-    
+    void render_gravity_arrow(const Transform3d& view_matrix, const Transform3d& projection_matrix);
+    void render_slicing_arrow(const Transform3d& view_matrix, const Transform3d& projection_matrix);
+    void render_slicing_plane(const Transform3d& view_matrix, const Transform3d& projection_matrix);
+
    // BBS: remove the bed picking logic
    // void register_raycasters_for_picking(const GLModel::Geometry& geometry, const Transform3d& trafo);
 };
@@ -1108,11 +1108,27 @@ void GLVolumeCollection::render(GLVolumeCollection::ERenderType       type,
            //use -1 ad a invalid type
            shader->set_uniform("print_volume.type", -1);
        }
-  
+        
+        const float normal_z = get_selection_support_normal_z();
+
+        // Compute up direction accounting for build plate tilt
+        Vec3f up_direction = Vec3f::UnitZ();
+        {
+            const DynamicPrintConfig& prt_cfg = GUI::wxGetApp().preset_bundle->printers.get_edited_preset().config;
+            double tilt_x_deg = prt_cfg.opt_float("build_plate_tilt_x");
+            double tilt_y_deg = prt_cfg.opt_float("build_plate_tilt_y");
+            if (tilt_x_deg != 0. || tilt_y_deg != 0.) {
+                double tilt_x_rad = Geometry::deg2rad(tilt_x_deg);
+                double tilt_y_rad = Geometry::deg2rad(tilt_y_deg);
+                up_direction = Vec3f(float(tan(tilt_y_rad)), float(tan(tilt_x_rad)), 1.f).normalized();
+            }
+        }
+
        shader->set_uniform("volume_world_matrix", volume.first->world_matrix());
        shader->set_uniform("slope.actived", m_slope.isGlobalActive && !volume.first->is_modifier && !volume.first->is_wipe_tower);
        shader->set_uniform("slope.volume_world_normal_matrix", static_cast<Matrix3f>(volume.first->world_matrix().matrix().block(0, 0, 3, 3).inverse().transpose().cast<float>()));
-        shader->set_uniform("slope.normal_z", support_normal_z);
+        shader->set_uniform("slope.normal_z", normal_z);
+        shader->set_uniform("slope.up_direction", up_direction);

 #if ENABLE_ENVIRONMENT_MAP
        unsigned int environment_texture_id = GUI::wxGetApp().plater()->get_environment_texture_id();
@@ -605,9 +605,17 @@ void ConfigManipulation::toggle_print_fff_options(DynamicPrintConfig *config, co
    const bool gcf_is_marlin_firmware = gcflavor == GCodeFlavor::gcfMarlinFirmware;
    const bool gcf_is_klipper = gcflavor == GCodeFlavor::gcfKlipper;

+    // Belt printer: detect early since it affects multiple toggle decisions below.
+    bool is_belt_printer = false;
+    {
+        const auto *belt_opt = preset_bundle->printers.get_edited_preset().config.option<ConfigOptionBool>("belt_printer");
+        if (belt_opt)
+            is_belt_printer = belt_opt->value;
+    }
+
    bool have_volumetric_extrusion_rate_slope = config->option<ConfigOptionFloat>("max_volumetric_extrusion_rate_slope")->value > 0;
    float have_volumetric_extrusion_rate_slope_segment_length = config->option<ConfigOptionFloat>("max_volumetric_extrusion_rate_slope_segment_length")->value;
-    toggle_field("enable_arc_fitting", !have_volumetric_extrusion_rate_slope);
+    toggle_field("enable_arc_fitting", !have_volumetric_extrusion_rate_slope && !is_belt_printer);
    toggle_line("max_volumetric_extrusion_rate_slope_segment_length", have_volumetric_extrusion_rate_slope);
    toggle_line("extrusion_rate_smoothing_external_perimeter_only", have_volumetric_extrusion_rate_slope);
    if(have_volumetric_extrusion_rate_slope) config->set_key_value("enable_arc_fitting", new ConfigOptionBool(false));
@@ -734,13 +742,20 @@ void ConfigManipulation::toggle_print_fff_options(DynamicPrintConfig *config, co
        }
    }

-    bool have_skirt = config->opt_int("skirt_loops") > 0;
+    // Belt printer: disable skirt, brim, raft, and draft shield controls.
+    bool have_skirt = config->opt_int("skirt_loops") > 0 && !is_belt_printer;
    toggle_field("skirt_height", have_skirt && config->opt_enum<DraftShield>("draft_shield") != dsEnabled);
    toggle_line("single_loop_draft_shield", have_skirt); // ORCA: Display one wall if skirt enabled
    for (auto el : {"skirt_type", "min_skirt_length", "skirt_distance", "skirt_start_angle", "skirt_speed", "draft_shield"})
        toggle_field(el, have_skirt);
+    if (is_belt_printer) {
+        toggle_field("skirt_loops", false);
+        toggle_field("skirt_height", false);
+    }

-    bool have_brim = (config->opt_enum<BrimType>("brim_type") != btNoBrim);
+    bool have_brim = (config->opt_enum<BrimType>("brim_type") != btNoBrim) && !is_belt_printer;
+    if (is_belt_printer)
+        toggle_field("brim_type", false);
    toggle_field("brim_object_gap", have_brim);
    toggle_field("brim_use_efc_outline", have_brim);
    toggle_field("combine_brims", have_brim);
@@ -764,7 +779,9 @@ void ConfigManipulation::toggle_print_fff_options(DynamicPrintConfig *config, co
    // Hide Elephant foot compensation layers if elefant_foot_compensation is not enabled
    toggle_line("elefant_foot_compensation_layers", config->opt_float("elefant_foot_compensation") > 0 || config->option<ConfigOptionPercent>("elefant_foot_layers_density")->get_abs_value(1.0f) < 1.0f);

-    bool have_raft = config->opt_int("raft_layers") > 0;
+    bool have_raft = config->opt_int("raft_layers") > 0 && !is_belt_printer;
+    if (is_belt_printer)
+        toggle_field("raft_layers", false);
    bool have_support_material = config->opt_bool("enable_support") || have_raft;

    SupportType support_type = config->opt_enum<SupportType>("support_type");
@@ -24,6 +24,8 @@
 #include "GLToolbar.hpp"
 #include "GUI_Preview.hpp"
 #include "libslic3r/Print.hpp"
+#include "libslic3r/BeltTransform.hpp"
+#include "libslic3r/GCode/MachineFrameTransform.hpp"
 #include "libslic3r/Layer.hpp"
 #include "Widgets/ProgressDialog.hpp"
 #include "MsgDialog.hpp"
@@ -1118,6 +1120,59 @@ std::vector<int> GCodeViewer::get_plater_extruder()
    return m_plater_extruder;
 }

+// Belt printers: compute the full machine->model back-transform from the print
+// config, so the "designed" (upright) G-code preview maps each toolpath vertex
+// back to Cartesian space. The G-code forward pipeline is (BeltGCodeWriter::
+// to_machine_coords):  gcode = MachineFrame( AxisRemap( X ) ), with X = model if
+// gcode_back_transform (write already un-rotated to Cartesian) else BeltForward(
+// model). So the inverse is:
+//   model = [BeltForward^-1 if !gcode_back_transform] . AxisRemap^-1 . MachineFrame^-1
+// All parts are config-driven affines -> handles any rotation/shear/scale/axis-
+// remap combination. (origin-snap is a per-instance translation that only shifts
+// position, not orientation, so it is intentionally omitted.)
+static Transform3d compute_belt_back_transform(const PrintConfig& cfg)
+{
+    if (!cfg.belt_printer.value)
+        return Transform3d::Identity();
+
+    MachineFrameTransform mft;
+    mft.init_from_config(cfg);
+    const Transform3d mf_inv = mft.is_active() ? Transform3d(mft.transform().inverse())
+                                               : Transform3d::Identity();
+
+    // Forward G-code axis remap as an affine matrix (out_i = sign * in[r_i % 3], plus a
+    // build-volume offset for Rev axes). This is the matrix form of the per-point
+    // GCodeWriter::apply_axis_remap (row convention: each OUTPUT axis selects an input
+    // axis + sign) and MUST stay in sync with it. The build-volume max matches what the
+    // writer is fed in GCode.cpp (printable_area max + printable_height). NB: this is the
+    // transpose of the column convention used by BeltTransformPipeline::build_preslice_remap
+    // — the two remaps are not interchangeable. (Follow-up: precompute this matrix once in
+    // GCodeWriter and share it with apply_axis_remap to remove the parallel encoding.)
+    Transform3d ar = Transform3d::Identity();
+    const int rr[3] = { int(cfg.gcode_remap_x.value), int(cfg.gcode_remap_y.value), int(cfg.gcode_remap_z.value) };
+    if (rr[0] != 0 || rr[1] != 1 || rr[2] != 2) {
+        BoundingBoxf bbox_bed(cfg.printable_area.values);
+        const Vec3d vmax(bbox_bed.max.x(), bbox_bed.max.y(), cfg.printable_height.value);
+        Matrix3d M = Matrix3d::Zero();
+        Vec3d    t = Vec3d::Zero();
+        for (int i = 0; i < 3; ++i) {
+            const int axis = rr[i] % 3;
+            if (rr[i] < 3)      M(i, axis) =  1.0;
+            else if (rr[i] < 6) M(i, axis) = -1.0;
+            else              { M(i, axis) = -1.0; t[i] = vmax[axis]; }
+        }
+        ar.linear()      = M;
+        ar.translation() = t;
+    }
+    const Transform3d ar_inv = ar.inverse();
+
+    Transform3d bf_inv = Transform3d::Identity();
+    if (!cfg.gcode_back_transform.value)
+        bf_inv = BeltTransformPipeline::build_forward_transform(cfg).inverse();
+
+    return bf_inv * ar_inv * mf_inv;
+}
+
 //BBS: always load shell at preview
 void GCodeViewer::load_as_gcode(const GCodeProcessorResult& gcode_result, const Print& print, const std::vector<std::string>& str_tool_colors,
                const std::vector<std::string>& str_color_print_colors, const BuildVolume& build_volume,
@@ -1125,13 +1180,25 @@ void GCodeViewer::load_as_gcode(const GCodeProcessorResult& gcode_result, const
 {
    m_loaded_as_preview = false;

+    // Belt printers: drive the designed/raw view UI (legend checkbox, hotkey B, canvas-toolbar
+    // menu item) from the loaded print here. Plater::set_bed_shape also calls set_belt_printer(),
+    // but only on bed-shape changes — not reliably on every slice/preview load — so the UI was
+    // staying hidden even though the (config-driven) designed view rendered. The tilt magnitude
+    // comes from the G-code header (gcode_result.belt_tilt_angle, abs of the slicing rotation).
+    m_belt_view_enabled = print.config().belt_printer.value;
+    m_belt_angle_deg    = gcode_result.belt_tilt_angle;
+
    const bool current_top_layer_only = m_viewer.is_top_layer_only_view_range();
    const bool required_top_layer_only = get_app_config()->get_bool("seq_top_layer_only");
    if (current_top_layer_only != required_top_layer_only)
        m_viewer.toggle_top_layer_only_view_range();

-    // avoid processing if called with the same gcode_result
-    if (m_last_result_id == gcode_result.id && wxGetApp().is_editor()) {
+    // avoid processing if called with the same gcode_result.
+    // Belt printers are exempt: the toolpath geometry fed to libvgcode depends on
+    // the current designed/raw view state (back-transform applied in convert), so
+    // re-running the conversion is required for the upright view and for toggling
+    // it (hotkey B) to take effect even when the G-code itself is unchanged.
+    if (m_last_result_id == gcode_result.id && wxGetApp().is_editor() && !print.config().belt_printer.value) {
        //BBS: add logs
        BOOST_LOG_TRIVIAL(info) << __FUNCTION__ << boost::format(": the same id %1%, return directly, result %2% ") % m_last_result_id % (&gcode_result);

@@ -1172,8 +1239,89 @@ void GCodeViewer::load_as_gcode(const GCodeProcessorResult& gcode_result, const
        return;
    }

-    // convert data from PrusaSlicer format to libvgcode format
-    libvgcode::GCodeInputData data = libvgcode::convert(gcode_result, str_tool_colors, str_color_print_colors, m_viewer);
+    // convert data from PrusaSlicer format to libvgcode format.
+    // Belt printers: when the "designed (upright) view" is active, back-transform
+    // the toolpath geometry into model/Cartesian space using the general belt
+    // inverse (handles any mesh rotation + shear + axis remap). When off, the raw
+    // machine-frame G-code is shown (useful for debugging the transform itself).
+    const bool is_belt = print.config().belt_printer.value;
+    Transform3d belt_inv = (is_belt && m_belt_show_designed)
+        ? compute_belt_back_transform(print.config()) : Transform3d::Identity();
+    // Belt: move positions are stored as gcode_Z + belt_z_origin (the start G-code's
+    // purge-blob advance baked into the machine-Z origin by its G92 Z0 resets). Subtract
+    // that constant before the linear back-transform so every toolpath maps to the model's
+    // belt coordinate. Without it the back-transform mixes the offset with the gantry-Y
+    // term, leaving a per-move designed-Y error that min-corner anchoring cannot remove
+    // when a bridge/keel move happens to cancel it at the bbox minimum.
+    if (is_belt && m_belt_show_designed && gcode_result.belt_z_origin != 0.0f)
+        belt_inv = belt_inv * Transform3d(Eigen::Translation3d(Vec3d(0.0, 0.0, -double(gcode_result.belt_z_origin))));
+    const bool apply_belt = is_belt && m_belt_show_designed
+        && !belt_inv.matrix().isApprox(Transform3d::Identity().matrix());
+    if (apply_belt) {
+        // The linear belt back-transform recovers the print's shape and orientation but not
+        // the per-object placement/lift translation: the object's position on the belt, the
+        // BeltSliceStrategy min-Z lift, and the centering pre-translate are applied OUTSIDE
+        // build_forward_transform() (see PrintObjectSlice.cpp), so its linear inverse leaves
+        // them un-undone. Uncorrected, the upright toolpaths float a fixed offset from the
+        // model shell. Recover the translation generally — independent of the offset's exact
+        // source or the axis remap — by anchoring the back-transformed object body onto the
+        // upright model bounding box (the same space the shells render in).
+        BoundingBoxf3 model_bb;
+        for (const PrintObject* po : print.objects())
+            for (const ModelInstance* mi : po->model_object()->instances)
+                model_bb.merge(po->model_object()->instance_bounding_box(*mi));
+        // Build the anchor bbox from surface toolpaths only. After the belt_z_origin
+        // correction the surface back-transforms onto the model, but a few elevated
+        // features (bridges/overhangs over the chevron gap) are mis-mapped by the linear
+        // inverse to well outside the model body; if one becomes the bbox minimum it
+        // drags the min-corner anchor by ~20mm. Drop moves that land clearly outside the
+        // (correct) model bbox — a geometric filter, not a role guess.
+        // Tolerance around the model bbox for outlier rejection, and the minimum fraction
+        // of MOVES (by count) the clip must retain before we trust it over the full bbox.
+        // Count, not bbox extent: a single far-flung outlier move (e.g. a belt-entry purge
+        // that maps to y~0) inflates the full bbox so much that a size-fraction test would
+        // wrongly reject the clip and re-include the outlier, dragging the min-corner anchor
+        // by ~the offset. By count the clip keeps ~100% of moves here and ~0% only when the
+        // object is genuinely offset from the belt entry (the real fall-back-to-full case).
+        constexpr double ANCHOR_CLIP_MARGIN_MM   = 10.0;
+        constexpr double ANCHOR_CLIP_MIN_KEEP    = 0.5;
+        BoundingBoxf3 tp_bb_clip, tp_bb_full;
+        size_t n_filtered = 0, n_clip = 0;
+        const double y_lo = model_bb.defined ? model_bb.min.y() - ANCHOR_CLIP_MARGIN_MM : -1e30;
+        const double y_hi = model_bb.defined ? model_bb.max.y() + ANCHOR_CLIP_MARGIN_MM :  1e30;
+        for (const GCodeProcessorResult::MoveVertex& mv : gcode_result.moves)
+            if (mv.type == EMoveType::Extrude && mv.layer_id >= 1) { // skip layer-0 prime/skirt
+                ++n_filtered;
+                const Vec3d p = belt_inv * mv.position.cast<double>();
+                tp_bb_full.merge(p);
+                if (p.y() >= y_lo && p.y() <= y_hi) {
+                    tp_bb_clip.merge(p);
+                    ++n_clip;
+                }
+            }
+        // Use the clipped bbox when it still holds the bulk of the moves (outliers removed).
+        // If the object sits far from the belt entry the toolpaths are grossly offset and the
+        // clip drops most of them — fall back to the full bbox so the min-corner anchor still
+        // recovers that gross translation rather than breaking.
+        const BoundingBoxf3& tp_bb =
+            (tp_bb_clip.defined && n_filtered > 0 &&
+             double(n_clip) >= ANCHOR_CLIP_MIN_KEEP * double(n_filtered)) ? tp_bb_clip : tp_bb_full;
+        if (model_bb.defined && tp_bb.defined) {
+            // Anchor the back-transformed toolpath body onto the upright model bbox by
+            // its MIN corner. (Center anchoring was tried and regressed when the toolpath
+            // and model bounding boxes differ in extent.) With the belt_z_origin
+            // correction above and the outlier-robust bbox below, the surface overlaps the
+            // shell to well under a millimetre when the object is at the belt entry; an
+            // object placed elsewhere in global-rotation mode still carries the placement
+            // translation, which this min-corner step recovers.
+            const Vec3d d = model_bb.min - tp_bb.min;
+            belt_inv = Transform3d(Eigen::Translation3d(d)) * belt_inv;
+            BOOST_LOG_TRIVIAL(debug) << "[BELT-PREVIEW] anchor d=[" << d.x() << "," << d.y() << "," << d.z()
+                << "] (clip kept " << n_clip << "/" << n_filtered << " moves)";
+        }
+    }
+    libvgcode::GCodeInputData data = libvgcode::convert(gcode_result, str_tool_colors, str_color_print_colors, m_viewer,
+        apply_belt ? &belt_inv : nullptr);

 //#define ENABLE_DATA_EXPORT 1
 //#if ENABLE_DATA_EXPORT
@@ -1342,6 +1490,7 @@ void GCodeViewer::load_as_gcode(const GCodeProcessorResult& gcode_result, const
    m_max_print_height = gcode_result.printable_height;
    m_z_offset = gcode_result.z_offset;

+
    // load_toolpaths(gcode_result, build_volume, exclude_bounding_box);
    
    // ORCA: Apply smart default view type when extruder count changes.
@@ -2301,7 +2450,14 @@ void GCodeViewer::load_shells(const Print& print, bool initialized, bool force_p
 void GCodeViewer::render_toolpaths()
 {
    const Camera& camera = wxGetApp().plater()->get_camera();
-    const libvgcode::Mat4x4 converted_view_matrix = libvgcode::convert(static_cast<Matrix4f>(camera.get_view_matrix().matrix().cast<float>()));
+    Matrix4f view = camera.get_view_matrix().matrix().cast<float>();
+    // Belt "designed" (upright) view is produced by back-transforming the toolpath
+    // GEOMETRY into model space at load time (see load_as_gcode ->
+    // compute_belt_back_transform -> libvgcode::convert). The camera is left untouched
+    // here; transforming the view as well would double-apply the inverse. Baking the
+    // transform into the geometry (not the camera) also keeps the bed and toolpaths in
+    // the same frame so they stay aligned.
+    const libvgcode::Mat4x4 converted_view_matrix = libvgcode::convert(view);
    const libvgcode::Mat4x4 converted_projetion_matrix = libvgcode::convert(static_cast<Matrix4f>(camera.get_projection_matrix().matrix().cast<float>()));
 #if VGCODE_ENABLE_COG_AND_TOOL_MARKERS
    m_viewer.set_cog_marker_scale_factor(m_cog_marker_fixed_screen_size ? 10.0f * m_cog_marker_size * camera.get_inv_zoom() : m_cog_marker_size);
@@ -4683,6 +4839,32 @@ void GCodeViewer::render_legend(float &legend_height, int canvas_width, int canv
    if (m_nozzle_nums > 1 && (m_viewer.get_view_type() == libvgcode::EViewType::Summary || m_viewer.get_view_type() == libvgcode::EViewType::ColorPrint)) // ORCA show only on summary and filament tab
        render_legend_color_arr_recommen(window_padding);

+    // Belt printer: toggle for viewing designed (upright) vs. machine-frame G-code.
+    // Rendered with a separator and hint text so users can find it easily.
+    if (m_belt_view_enabled) {
+        ImGui::Spacing();
+        ImGui::Separator();
+        ImGui::Spacing();
+        ImGui::Dummy({ window_padding, 0 });
+        ImGui::SameLine();
+        ImGui::TextColored(ImVec4(0.f, 0.59f, 0.53f, 1.f), "%s", _u8L("Belt Printer").c_str());
+        ImGui::Dummy({ window_padding, 0 });
+        ImGui::SameLine();
+        // Checked = show the raw machine-frame G-code (designed/upright view off). Worded to
+        // match the canvas-toolbar menu item "Show raw G-code (belt only)". m_belt_show_designed
+        // is the inverse of this checkbox, so bind a temporary and flip it on change.
+        bool show_raw = !m_belt_show_designed;
+        if (ImGui::Checkbox(_u8L("Show raw G-code (belt only) [B]").c_str(), &show_raw)) {
+            m_belt_show_designed = !show_raw;
+            // The designed-view back-transform is baked into the toolpath geometry at load
+            // time, so the toggle only takes effect once the preview is re-converted. Defer
+            // the refresh to the next event-loop tick (CallAfter) to avoid re-entering the
+            // preview load from inside legend rendering.
+            if (Plater* plater = wxGetApp().plater())
+                plater->CallAfter([plater]() { plater->refresh_belt_view(); });
+        }
+    }
+
    legend_height = ImGui::GetCurrentWindow()->Size.y;
    imgui.end();
    ImGui::PopStyleColor(7);
@@ -243,6 +243,11 @@ private:
 mutable bool m_no_render_path { false };
    bool m_is_dark = false;

+    bool  m_belt_view_enabled = false;
+    float m_belt_angle_deg = 0.f;
+    bool  m_belt_show_designed = true;   // Toggle: designed (upright, back-transformed) view by default;
+                                         // turn off (hotkey B) to inspect the raw machine-frame G-code.
+
    libvgcode::Viewer m_viewer;
    bool m_loaded_as_preview{ false };

@@ -342,6 +347,11 @@ public:

    void export_toolpaths_to_obj(const char* filename) const;

+    void set_belt_printer(bool enabled, float angle_deg) { m_belt_view_enabled = enabled; m_belt_angle_deg = angle_deg; }
+    bool is_belt_view() const { return m_belt_view_enabled && m_belt_angle_deg > 0.f; }
+    void toggle_belt_show_designed() { if (m_belt_view_enabled) m_belt_show_designed = !m_belt_show_designed; }
+    bool is_belt_show_designed() const { return m_belt_show_designed; }
+
    size_t get_extruders_count() { return m_extruders_count; }
    void push_combo_style();
    void pop_combo_style();
@@ -3506,8 +3506,20 @@ void GLCanvas3D::on_char(wxKeyEvent& evt)
                    post_event(SimpleEvent(EVT_GLCANVAS_ARRANGE));
                break;
            }
-        //case 'B':
-        //case 'b': { zoom_to_bed(); break; }
+        case 'B':
+        case 'b': {
+            // Toggle belt printer "show designed" view when in G-code preview with belt mode active.
+            if (dynamic_cast<Preview*>(m_canvas->GetParent()) != nullptr &&
+                m_gcode_viewer.is_belt_view()) {
+                m_gcode_viewer.toggle_belt_show_designed();
+                // The designed-view back-transform is baked into the toolpath geometry at load
+                // time, so the toggle only takes visual effect once the preview is re-converted.
+                if (Plater* plater = wxGetApp().plater())
+                    plater->refresh_belt_view();
+                m_dirty = true;
+            }
+            break;
+        }
        case 'C':
        case 'c': { wxGetApp().toggle_show_gcode_window(); m_dirty = true; request_extra_frame(); break; }
        //case 'G':
@@ -9182,6 +9194,21 @@ void GLCanvas3D::_render_canvas_toolbar()
            ImGui::TextColored(enable ? ImVec4(1,1,1,1) : ImGui::GetStyleColorVec4(ImGuiCol_TextDisabled), "%s", into_u8(condition ? ImGui::VisibleIcon : ImGui::HiddenIcon).c_str());
        };

+        // Belt printers, G-code preview only: toggle the designed (upright) view vs the raw
+        // machine-frame G-code. Same state as hotkey B and the legend checkbox; the reload is
+        // deferred (CallAfter) so the preview is not rebuilt mid-render.
+        if (m_canvas_type == ECanvasType::CanvasPreview && m_gcode_viewer.is_belt_view()) {
+            create_menu_item( _utf8(L("Show raw G-code (belt only)")),
+                true,
+                !m_gcode_viewer.is_belt_show_designed(), // eye lit = raw machine-frame G-code (designed view off)
+                [this, p]{
+                    m_gcode_viewer.toggle_belt_show_designed();
+                    p->CallAfter([p]{ p->refresh_belt_view(); });
+                }
+            );
+            ImGui::Separator();
+        }
+
        create_menu_item( _utf8(L("3D Navigator")),
            m_canvas_type != ECanvasType::CanvasAssembleView, // not work on assembly
            wxGetApp().show_3d_navigator(),
@@ -63,6 +63,7 @@ static SettingsFactory::Bundle FREQ_SETTINGS_BUNDLE_FFF =
    { L("Support")     , { "enable_support", "support_type", "support_threshold_angle", "support_threshold_overlap",
                                    "support_base_pattern", "support_on_build_plate_only","support_critical_regions_only",
                                    "support_remove_small_overhang",
+                                    "build_plate_tilt_x", "build_plate_tilt_y",
                                    "support_base_pattern_spacing", "support_expansion"}},
    //BBS
    { L("Flush options")         , { "flush_into_infill", "flush_into_objects", "flush_into_support"} }
@@ -92,7 +93,8 @@ std::map<std::string, std::vector<SimpleSettingData>>  SettingsFactory::OBJECT_C
                    {"support_bottom_z_distance", "",20},{"support_top_z_distance", "",21},{"support_base_pattern", "",22},{"support_base_pattern_spacing", "",23},
                    {"support_interface_top_layers", "",24},{"support_interface_bottom_layers", "",25},{"support_interface_spacing", "",26},{"support_bottom_interface_spacing", "",27},
                    {"support_object_xy_distance", "",28}, {"bridge_no_support", "",29},{"max_bridge_length", "",30},{"support_critical_regions_only", "",31},{"support_remove_small_overhang","",32},
-                    {"support_object_first_layer_gap","",33}
+                    {"build_plate_tilt_x","",33},{"build_plate_tilt_y","",34},
+                    {"support_object_first_layer_gap","",35}
                    }},
    { L("Speed"), {{"support_speed", "",12}, {"support_interface_speed", "",13}
                  }}
@@ -2593,7 +2593,7 @@ void ObjectList::load_mesh_object(const TriangleMesh &mesh, const wxString &name
    Slic3r::save_object_mesh(*new_object);

    // BBS: find an empty cell to put the copied object
-    auto start_point = wxGetApp().plater()->build_volume().bounding_volume2d().center();
+    auto start_point = wxGetApp().plater()->build_volume().bed_center();
    auto empty_cell  = wxGetApp().plater()->canvas3D()->get_nearest_empty_cell({start_point(0), start_point(1)});

    new_object->instances[0]->set_offset(center ? to_3d(Vec2d(empty_cell(0), empty_cell(1)), -new_object->origin_translation.z()) : bb.center());
@@ -351,6 +351,17 @@ void Preview::reload_print(bool only_gcode)
    m_only_gcode = only_gcode;
 }

+void Preview::refresh_belt_view()
+{
+    // Re-run the G-code preview conversion so the belt "designed view" toggle takes effect
+    // (the back-transform is baked into the toolpath geometry in GCodeViewer::load_as_gcode,
+    // and belt printers are exempt from the same-result-id load cache so the re-convert runs).
+    // Reset m_loaded_print to bypass the "already loaded" guard the way reload_print does, but
+    // keep the current layer (Z) range and only-gcode mode so the view doesn't jump on toggle.
+    m_loaded_print = nullptr;
+    load_print(true /*keep_z_range*/, m_only_gcode);
+}
+
 //BBS: always load shell at preview
 void Preview::load_shells(const Print& print, bool force_previewing)
 {
@@ -141,6 +141,8 @@ public:
    //BBS: add only gcode mode
    void load_print(bool keep_z_range = false, bool only_gcode = false);
    void reload_print(bool only_gcode = false);
+    // Belt printers: re-convert the G-code preview so the "designed view" toggle takes effect.
+    void refresh_belt_view();
    //BBS: always load shell at preview
    void load_shells(const Print& print, bool force_previewing = false);
    void reset_shells();
@@ -526,6 +526,14 @@ int GLGizmoFdmSupports::get_selection_support_threshold_angle()
    return auto_support ? support_threshold_angle : 0;
 }

+std::pair<double, double> GLGizmoFdmSupports::get_build_plate_tilt()
+{
+    const DynamicPrintConfig& cfg = wxGetApp().preset_bundle->printers.get_edited_preset().config;
+    double tilt_x = cfg.opt_float("build_plate_tilt_x");
+    double tilt_y = cfg.opt_float("build_plate_tilt_y");
+    return {tilt_x, tilt_y};
+}
+
 void GLGizmoFdmSupports::select_facets_by_angle(float threshold_deg, bool block)
 {
    float threshold = (float(M_PI)/180.f)*threshold_deg;
@@ -533,6 +541,12 @@ void GLGizmoFdmSupports::select_facets_by_angle(float threshold_deg, bool block)
    const ModelObject* mo = m_c->selection_info()->model_object();
    const ModelInstance* mi = mo->instances[selection.get_instance_idx()];

+    // Compute gravity direction accounting for build plate tilt
+    auto [tilt_x_deg, tilt_y_deg] = get_build_plate_tilt();
+    double tilt_x_rad = tilt_x_deg * M_PI / 180.0;
+    double tilt_y_rad = tilt_y_deg * M_PI / 180.0;
+    Vec3d gravity_dir = Vec3d(-tan(tilt_y_rad), -tan(tilt_x_rad), -1.0).normalized();
+
    int mesh_id = -1;
    for (const ModelVolume* mv : mo->volumes) {
        if (! mv->is_model_part())
@@ -541,10 +555,8 @@ void GLGizmoFdmSupports::select_facets_by_angle(float threshold_deg, bool block)
        ++mesh_id;

        const Transform3d trafo_matrix = mi->get_matrix_no_offset() * mv->get_matrix_no_offset();
-        Vec3f down  = (trafo_matrix.inverse() * (-Vec3d::UnitZ())).cast<float>().normalized();
-        Vec3f limit = (trafo_matrix.inverse() * Vec3d(std::sin(threshold), 0, -std::cos(threshold))).cast<float>().normalized();
-
-        float dot_limit = limit.dot(down);
+        Vec3f down  = (trafo_matrix.inverse() * gravity_dir).cast<float>().normalized();
+        float dot_limit = std::cos(threshold);

        // Now calculate dot product of vert_direction and facets' normals.
        int idx = 0;
@@ -60,6 +60,7 @@ private:
    void select_facets_by_angle(float threshold, bool block);
    // BBS
    int get_selection_support_threshold_angle();
+    std::pair<double, double> get_build_plate_tilt();

    int m_support_threshold_angle = -1;

@@ -73,6 +73,18 @@ GLGizmoPainterBase::ClippingPlaneDataWrapper GLGizmoPainterBase::get_clipping_pl
    return clp_data_out;
 }

+Vec3f GLGizmoPainterBase::get_tilt_up_direction() const
+{
+    const DynamicPrintConfig& cfg = wxGetApp().preset_bundle->printers.get_edited_preset().config;
+    double tilt_x_deg = cfg.opt_float("build_plate_tilt_x");
+    double tilt_y_deg = cfg.opt_float("build_plate_tilt_y");
+    if (tilt_x_deg == 0. && tilt_y_deg == 0.)
+        return Vec3f::UnitZ();
+    double tilt_x_rad = Geometry::deg2rad(tilt_x_deg);
+    double tilt_y_rad = Geometry::deg2rad(tilt_y_deg);
+    return Vec3f(float(tan(tilt_y_rad)), float(tan(tilt_x_rad)), 1.f).normalized();
+}
+
 void GLGizmoPainterBase::render_triangles(const Selection& selection) const
 {
    auto* shader = wxGetApp().get_shader("mm_gouraud");
@@ -119,11 +131,15 @@ void GLGizmoPainterBase::render_triangles(const Selection& selection) const
        float normal_z = -::cos(Geometry::deg2rad(m_highlight_by_angle_threshold_deg));
        Matrix3f normal_matrix = static_cast<Matrix3f>(trafo_matrix.matrix().block(0, 0, 3, 3).inverse().transpose().cast<float>());

+        // Compute up direction accounting for build plate tilt
+        Vec3f up_direction = get_tilt_up_direction();
+
        shader->set_uniform("volume_world_matrix", trafo_matrix);
        shader->set_uniform("volume_mirrored", is_left_handed);
        shader->set_uniform("slope.actived", m_parent.is_using_slope());
        shader->set_uniform("slope.volume_world_normal_matrix", normal_matrix);
        shader->set_uniform("slope.normal_z", normal_z);
+        shader->set_uniform("slope.up_direction", up_direction);
        m_triangle_selectors[mesh_id]->render(m_imgui, trafo_matrix);

        if (is_left_handed)
@@ -691,7 +707,7 @@ bool GLGizmoPainterBase::gizmo_event(SLAGizmoEventType action, const Vec2d& mous
                        mi->get_assemble_transformation().get_matrix() * mo->volumes[m_rr.mesh_id]->get_matrix() :
                        mi->get_transformation().get_matrix() * mo->volumes[m_rr.mesh_id]->get_matrix();
                    m_triangle_selectors[m_rr.mesh_id]->seed_fill_select_triangles(m_rr.hit, int(m_rr.facet), trafo_matrix_not_translate, this->get_clipping_plane_in_volume_coordinates(trafo_matrix), m_smart_fill_angle,
-                                                                                   m_paint_on_overhangs_only ? m_highlight_by_angle_threshold_deg : 0.f, true);
+                                                                                   m_paint_on_overhangs_only ? m_highlight_by_angle_threshold_deg : 0.f, true, get_tilt_up_direction());
                    m_triangle_selectors[m_rr.mesh_id]->request_update_render_data();
                    m_seed_fill_last_mesh_id = m_rr.mesh_id;
                }
@@ -803,7 +819,7 @@ bool GLGizmoPainterBase::gizmo_event(SLAGizmoEventType action, const Vec2d& mous
                std::unique_ptr<TriangleSelector::Cursor> cursor = TriangleSelector::SinglePointCursor::cursor_factory(phr.z_world,
                    camera_pos, m_cursor_height, trafo_matrix, clp);
                m_triangle_selectors[mesh_idx]->select_patch(int(phr.first_facet_idx), std::move(cursor), new_state, trafo_matrix_not_translate,
-                    m_triangle_splitting_enabled, m_paint_on_overhangs_only ? m_highlight_by_angle_threshold_deg : 0.f);
+                    m_triangle_splitting_enabled, m_paint_on_overhangs_only ? m_highlight_by_angle_threshold_deg : 0.f, get_tilt_up_direction());

                m_triangle_selectors[mesh_idx]->request_update_render_data(true);
                m_last_mouse_click = _mouse_position;
@@ -855,7 +871,7 @@ bool GLGizmoPainterBase::gizmo_event(SLAGizmoEventType action, const Vec2d& mous
                    m_triangle_selectors[mesh_idx]->seed_fill_apply_on_triangles(new_state);
                    if (m_tool_type == ToolType::SMART_FILL)
                        m_triangle_selectors[mesh_idx]->seed_fill_select_triangles(mesh_hit, facet_idx, trafo_matrix_not_translate, clp, m_smart_fill_angle,
-                                                                                       m_paint_on_overhangs_only ? m_highlight_by_angle_threshold_deg : 0.f, true);
+                                                                                       m_paint_on_overhangs_only ? m_highlight_by_angle_threshold_deg : 0.f, true, get_tilt_up_direction());
                    else if (m_tool_type == ToolType::BRUSH && m_cursor_type == TriangleSelector::CursorType::POINTER)
                        // BBS: add infill_angle parameter
                        m_triangle_selectors[mesh_idx]->bucket_fill_select_triangles(mesh_hit, facet_idx, clp, -1.f, false, true);
@@ -874,12 +890,12 @@ bool GLGizmoPainterBase::gizmo_event(SLAGizmoEventType action, const Vec2d& mous
                                                                                                                                   camera_pos, m_cursor_radius,
                                                                                                                                   m_cursor_type, trafo_matrix, clp);
                    m_triangle_selectors[mesh_idx]->select_patch(int(first_position.facet_idx), std::move(cursor), new_state, trafo_matrix_not_translate,
-                                                                 m_triangle_splitting_enabled, m_paint_on_overhangs_only ? m_highlight_by_angle_threshold_deg : 0.f);
+                                                                 m_triangle_splitting_enabled, m_paint_on_overhangs_only ? m_highlight_by_angle_threshold_deg : 0.f, get_tilt_up_direction());
                } else {
                    for (auto first_position_it = projected_mouse_positions.cbegin(); first_position_it != projected_mouse_positions.cend() - 1; ++first_position_it) {
                        auto second_position_it = first_position_it + 1;
                        std::unique_ptr<TriangleSelector::Cursor> cursor = TriangleSelector::DoublePointCursor::cursor_factory(first_position_it->mesh_hit, second_position_it->mesh_hit, camera_pos, m_cursor_radius, m_cursor_type, trafo_matrix, clp);
-                        m_triangle_selectors[mesh_idx]->select_patch(int(first_position_it->facet_idx), std::move(cursor), new_state, trafo_matrix_not_translate, m_triangle_splitting_enabled, m_paint_on_overhangs_only ? m_highlight_by_angle_threshold_deg : 0.f);
+                        m_triangle_selectors[mesh_idx]->select_patch(int(first_position_it->facet_idx), std::move(cursor), new_state, trafo_matrix_not_translate, m_triangle_splitting_enabled, m_paint_on_overhangs_only ? m_highlight_by_angle_threshold_deg : 0.f, get_tilt_up_direction());
                    }
                }
            }
@@ -953,7 +969,7 @@ bool GLGizmoPainterBase::gizmo_event(SLAGizmoEventType action, const Vec2d& mous
        const TriangleSelector::ClippingPlane &clp = this->get_clipping_plane_in_volume_coordinates(trafo_matrix);
        if (m_tool_type == ToolType::SMART_FILL)
            m_triangle_selectors[m_rr.mesh_id]->seed_fill_select_triangles(m_rr.hit, int(m_rr.facet), trafo_matrix_not_translate, clp, m_smart_fill_angle,
-                                                                           m_paint_on_overhangs_only ? m_highlight_by_angle_threshold_deg : 0.f);
+                                                                           m_paint_on_overhangs_only ? m_highlight_by_angle_threshold_deg : 0.f, false, get_tilt_up_direction());
        else if (m_tool_type == ToolType::BRUSH && m_cursor_type == TriangleSelector::CursorType::POINTER)
            // BBS: add infill_angle parameter
            m_triangle_selectors[m_rr.mesh_id]->bucket_fill_select_triangles(m_rr.hit, int(m_rr.facet), clp, -1.f, false);
@@ -281,6 +281,9 @@ protected:
    bool     m_paint_on_overhangs_only          = false;
    float    m_highlight_by_angle_threshold_deg = 0.f;

+    // Returns the up direction accounting for build plate tilt (default: UnitZ)
+    Vec3f get_tilt_up_direction() const;
+
    GLModel m_circle;
    Vec2d m_old_center{ Vec2d::Zero() };
    float m_old_cursor_radius{ 0.0f };