Merge upstream main: cyclic print ordering, brim overlap fix, perimeter and support fixes

src/libslic3r/AppConfig.cpp

@@ -202,10 +202,25 @@ void AppConfig::set_defaults()
     if (get("seq_top_layer_only").empty())
         set("seq_top_layer_only", "1");
 
-    // ORCA: darken layers below the current one while scrubbing the preview (ported from preFlight)
+    // ORCA: darken the layers the preview layer slider is not scrubbed to
     if (get("preview_dim_previous_layers").empty())
         set_bool("preview_dim_previous_layers", false);
 
+    // ORCA: brightness of those dimmed layers, in percent. 0 = black, capped at 99 because
+    // 100 would render them unchanged, which is what disabling the option already does
+    if (get("preview_dim_previous_layers_brightness").empty())
+        set("preview_dim_previous_layers_brightness", "40");
+    else {
+        int brightness = 40;
+        try {
+            brightness = std::stoi(get("preview_dim_previous_layers_brightness"));
+        }
+        catch (...) {
+            brightness = 40;
+        }
+        set("preview_dim_previous_layers_brightness", std::to_string(std::max(0, std::min(brightness, 99))));
+    }
+
     if (get("filaments_area_preferred_count").empty())
         set("filaments_area_preferred_count", "10");
 

src/libslic3r/Brim.cpp

@@ -32,15 +32,13 @@ static void append_and_translate(ExPolygons &dst, const ExPolygons &src, const P
     for (; dst_idx < dst.size(); ++dst_idx)
         dst[dst_idx].translate(instance_shift);
 }
-// BBS: generate brim area by objs
-static void append_and_translate(ExPolygons& dst, const ExPolygons& src,
-    const PrintInstance& instance, size_t instance_idx, std::map<ObjectInstanceID, ExPolygons>& brimAreaMap) {
+// Orca: Translate the brim area into print coordinates and store it per instance.
+static void append_and_translate(const ExPolygons& src, const PrintInstance& instance,
+    size_t instance_idx, std::map<ObjectInstanceID, ExPolygons>& brimAreaMap) {
     ExPolygons srcShifted = src;
     Point instance_shift = instance.shift_without_plate_offset();
-    for (size_t src_idx = 0; src_idx < srcShifted.size(); ++src_idx)
-        srcShifted[src_idx].translate(instance_shift);
-    srcShifted = diff_ex(srcShifted, dst);
-    //expolygons_append(dst, temp2);
+    for (ExPolygon& expoly : srcShifted)
+        expoly.translate(instance_shift);
     expolygons_append(brimAreaMap[{ instance.print_object->id(), instance_idx }], std::move(srcShifted));
 }
 
@@ -572,7 +570,7 @@ static ExPolygons outer_inner_brim_area(const Print& print,
                 for (size_t instance_idx = 0; instance_idx < object->instances().size(); ++instance_idx) {
                     const PrintInstance& instance = object->instances()[instance_idx];
                     if (!brim_area_object.empty())
-                        append_and_translate(brim_area, brim_area_object, instance, instance_idx, brimAreaMap);
+                        append_and_translate(brim_area_object, instance, instance_idx, brimAreaMap);
                     append_and_translate(no_brim_area, no_brim_area_object, instance);
                     append_and_translate(holes, holes_object, instance);
                     append_and_translate(objectIslands, objectIsland, instance);
@@ -875,6 +873,14 @@ void make_brim(const Print& print, PrintTryCancel try_cancel, Polygons& islands_
     ExPolygons           islands_area_ex = outer_inner_brim_area(print,
         float(flow.scaled_spacing()), brimAreaMap, objPrintVec, printExtruders);
 
+    if (!print.config().combine_brims) {
+        ExPolygons claimed_area;
+        for (auto& [_, areas] : brimAreaMap) {
+            areas = diff_ex(areas, claimed_area);
+            expolygons_append(claimed_area, areas);
+        }
+    }
+
     // BBS: Find boundingbox of the first layer
     for (const ObjectID printObjID : print.print_object_ids()) {
         BoundingBox bbx;

src/libslic3r/CMakeLists.txt

@@ -248,6 +248,8 @@ set(lisbslic3r_sources
     GCode/Thumbnails.hpp
     GCode/ToolOrdering.cpp
     GCode/ToolOrdering.hpp
+    GCode/OrderingStrategies.cpp
+    GCode/OrderingStrategies.hpp
     GCode/WipeTower2.cpp
     GCode/WipeTower2.hpp
     GCode/WipeTower.cpp

src/libslic3r/Format/STEP.hpp

@@ -78,7 +78,7 @@ public:
     Standard_Boolean UserBreak() override { return should_stop.load(); }
 
     void Show(const Message_ProgressScope&, const Standard_Boolean) override {
-        std::cout << "Progress: " << GetPosition() << "%" << std::endl;
+        std::cout << "Progress: " << std::fixed << std::setprecision(2) << 100.0 * GetPosition() << "%" << std::endl;
     }
 private:
     std::atomic<bool>& should_stop;

src/libslic3r/GCode.cpp

@@ -15,6 +15,7 @@
 #include "GCode/Thumbnails.hpp"
 #include "GCode/WipeTower.hpp"
 #include "ShortestPath.hpp"
+#include "GCode/OrderingStrategies.hpp"
 #include "Print.hpp"
 #include "Utils.hpp"
 #include "ClipperUtils.hpp"
@@ -2841,6 +2842,7 @@ void GCode::_do_export(Print& print, GCodeOutputStream &file, ThumbnailsGenerato
     m_role_based_fan_marker_layer.fill(-1);
 
     m_fan_mover.release();
+    m_ordering_cache.clear();
     
     m_writer.set_is_bbl_machine(is_bbl_printers);
 
@@ -3161,11 +3163,20 @@ void GCode::_do_export(Print& print, GCodeOutputStream &file, ThumbnailsGenerato
         // In non-sequential print, the printing extruders may have been modified by the extruder switches stored in Model::custom_gcode_per_print_z.
         // Therefore initialize the printing extruders from there.
         this->set_extruders(tool_ordering.all_extruders());
-        print_object_instances_ordering = 
-            // By default, order object instances using a nearest neighbor search.
-            print.config().print_order == PrintOrder::Default ? chain_print_object_instances(print)
+        print_object_instances_ordering =
+            // By default, order object instances using nearest-neighbor chaining plus
+            // 2-opt and crossing-removal post-processing.
+            (print.config().print_order == PrintOrder::Default ? chain_print_object_instances(print)
+            // Snake: serpentine row traversal + 2-opt
+            : (print.config().print_order == PrintOrder::Snake ? chain_print_object_instances_snake(print)
+            // Best of all: run every strategy, pick the shortest total path
+            : (print.config().print_order == PrintOrder::BestOfStrategies ? chain_print_object_instances_best_of(print)
             // Otherwise same order as the object list
-            : sort_object_instances_by_model_order(print);
+            : sort_object_instances_by_model_order(print))));
+
+
+
+
     }
     if (initial_extruder_id == (unsigned int)-1) {
         // Nothing to print!
@@ -5658,7 +5669,9 @@ LayerResult GCode::process_layer(
     //Calibration Layer-specific GCode
     switch (print.calib_mode()) {
         case CalibMode::Calib_PA_Tower: {
-            gcode += writer().set_pressure_advance(print.calib_params().start + static_cast<int>(print_z) * print.calib_params().step);
+            gcode += writer().set_pressure_advance(this->interpolate_value_across_layers(static_cast<float>(print.calib_params().start),
+                                                                                         static_cast<float>(print.calib_params().end),
+                                                                                         static_cast<float>(print.calib_params().step)));
             break;
         }
         case CalibMode::Calib_Temp_Tower: {
@@ -5666,7 +5679,12 @@ LayerResult GCode::process_layer(
             break;
         }
         case CalibMode::Calib_VFA_Tower: {
-            auto _speed = print.calib_params().start + std::floor(print_z / 5.0) * print.calib_params().step;
+            // Step the outer wall speed from start to end across the tower's layers. Plater::calib_VFA sizes the
+            // geometry so each speed step spans one visual block (a fixed number of layers), so the layer-based
+            // stepping stays aligned with the blocks regardless of nozzle size / layer height.
+            float _speed = this->interpolate_value_across_layers(static_cast<float>(print.calib_params().start),
+                                                                 static_cast<float>(print.calib_params().end),
+                                                                 static_cast<float>(print.calib_params().step));
             m_calib_config.set_key_value("outer_wall_speed", new ConfigOptionFloatsNullable({std::round(_speed)}));
             break;
         }
@@ -6127,41 +6145,128 @@ LayerResult GCode::process_layer(
     if (m_farthest_point_timelapse.enabled)
         compute_farthest_point(layers, most_used_extruder, support_filaments);
 
-    std::map<unsigned int, std::vector<InstanceToPrint>> filament_to_print_instances;
+    // Per filament: instances to print, and the visit sequence over them. Island-level ordering
+    // may visit an instance more than once per layer; otherwise one visit per instance.
+    std::map<unsigned int, std::pair<std::vector<InstanceToPrint>, std::vector<InstanceVisit>>> filament_to_print_instances;
     {
+        // Order individual islands rather than whole instances. Off for by-object sequencing,
+        // sequential printing, and the explicit AsObjectList order, which tour whole instances.
+        const bool island_level_ordering = print.config().print_sequence != PrintSequence::ByObject &&
+            single_object_instance_idx == size_t(-1) &&
+            print.config().print_order != PrintOrder::AsObjectList;
         for (unsigned int filament_id : layer_tools.extruders) {
             auto objects_by_extruder_it = by_extruder.find(filament_id);
             if (objects_by_extruder_it == by_extruder.end()) continue;
 
+            auto &filament_plan = filament_to_print_instances[filament_id];
+
+            if (!island_level_ordering) {
+                // One visit per instance, printing all of its islands.
+                filament_plan.first = sort_print_object_instances(objects_by_extruder_it->second, layers, ordering, single_object_instance_idx);
+                filament_plan.second.reserve(filament_plan.first.size());
+                for (size_t i = 0; i < filament_plan.first.size(); ++i)
+                    filament_plan.second.push_back({i, {}, true});
+                continue;
+            }
+
             int   plate_idx = print.get_plate_index();
             Point wt_pos(print.config().wipe_tower_x.get_at(plate_idx), print.config().wipe_tower_y.get_at(plate_idx));
 
+            // Build the instances and one tour node per non-empty island (a single node for
+            // instances without chainable islands). Positions quantized to 1 mm so small
+            // centroid drift between layers still hits the tour cache below.
             std::vector<GCode::ObjectByExtruder> &objects_by_extruder = objects_by_extruder_it->second;
-            std::vector<const PrintObject *>      print_objects;
-            for (int obj_idx = 0; obj_idx < objects_by_extruder.size(); obj_idx++) {
-                auto &object_by_extruder = objects_by_extruder[obj_idx];
+            std::vector<InstanceToPrint> &instances = filament_plan.first;
+            std::vector<IslandOrderNode> nodes;
+            std::vector<size_t>          node_instances;
+            auto quantize_to_mm = [](const Point &pt) -> Point {
+                const coord_t grid = coord_t(scale_(1.));
+                // Round to the nearest 1 mm symmetrically (integer division truncates toward
+                // zero, which would make the bucket straddling the origin twice as wide).
+                auto q = [grid](coord_t v) -> coord_t {
+                    return ((v >= 0 ? v + grid / 2 : v - grid / 2) / grid) * grid;
+                };
+                return Point(q(pt.x()), q(pt.y()));
+            };
+            for (ObjectByExtruder &object_by_extruder : objects_by_extruder) {
                 if (object_by_extruder.islands.empty() && (object_by_extruder.support == nullptr || object_by_extruder.support->empty())) continue;
 
-                print_objects.push_back(print.get_object(obj_idx));
+                const size_t       layer_id     = &object_by_extruder - objects_by_extruder.data();
+                const PrintObject *print_object = layers[layer_id].original_object;
+                if (print_object == nullptr)
+                    continue;
+                const Layer *obj_layer = layers[layer_id].object_layer;
+                std::vector<ObjectByExtruder::Island> &islands = object_by_extruder.islands;
+                const bool islands_chainable = obj_layer != nullptr && islands.size() == obj_layer->lslices.size() + 1;
+                for (size_t instance_id = 0; instance_id < print_object->instances().size(); ++instance_id) {
+                    const size_t instance_idx = instances.size();
+                    instances.emplace_back(object_by_extruder, layer_id, *print_object, instance_id,
+                                           print_object->instances()[instance_id].model_instance->get_labeled_id());
+                    const Point &shift = print_object->instances()[instance_id].shift;
+                    const size_t first_node = nodes.size();
+                    if (islands_chainable)
+                        for (size_t i = 0; i + 1 < islands.size(); ++i)
+                            if (!islands[i].by_region.empty()) {
+                                nodes.push_back({print_object->id(), instance_id, i,
+                                                 quantize_to_mm(obj_layer->lslices[i].contour.centroid() + shift)});
+                                node_instances.emplace_back(instance_idx);
+                            }
+                    if (nodes.size() == first_node) {
+                        // No chainable islands: tour the whole instance as one stop.
+                        nodes.push_back({print_object->id(), instance_id, size_t(-1), quantize_to_mm(shift)});
+                        node_instances.emplace_back(instance_idx);
+                    }
+                }
             }
 
-            std::vector<const PrintInstance *> new_ordering = chain_print_object_instances(print_objects, &wt_pos);
-            std::reverse(new_ordering.begin(), new_ordering.end());
+            // Reuse the cached tour while this filament's island layout is unchanged.
+            auto &cache_entry = m_ordering_cache[filament_id];
+            if (!(cache_entry.first == nodes)) {
+                cache_entry.first = nodes;
+                Points node_points;
+                node_points.reserve(nodes.size());
+                for (const IslandOrderNode &node : nodes)
+                    node_points.emplace_back(node.pos);
+                std::vector<size_t> tour = order_points_with_strategy(node_points, print.config().print_order, &wt_pos);
+                // Chained starting near the wipe tower, reversed so the layer ends near it.
+                std::reverse(tour.begin(), tour.end());
 
-            if (print.config().print_sequence == PrintSequence::ByObject) {
-                filament_to_print_instances[filament_id] = sort_print_object_instances(objects_by_extruder_it->second, layers, ordering, single_object_instance_idx);
-            } else {
-                
-                // PrintSequence::ByLayer to use global ordering ( per object ordering ) if intra-layer order PrintOrder::AsObjectList is specified while keeping behaviour of PrintSequence::ByLayer
-                const std::vector<const PrintInstance*>* ordering_for_filament = (print.config().print_order == PrintOrder::AsObjectList && ordering != nullptr) ? ordering: &new_ordering;
-                filament_to_print_instances[filament_id] = sort_print_object_instances(objects_by_extruder_it->second, layers, ordering_for_filament, single_object_instance_idx);
+                // Group consecutive tour stops of the same instance into visits.
+                std::vector<InstanceVisit> visits;
+                std::vector<bool> instance_seen(instances.size(), false);
+                std::vector<int>  last_visit_of_instance(instances.size(), -1);
+                for (size_t node_idx : tour) {
+                    const size_t instance_idx = node_instances[node_idx];
+                    if (visits.empty() || visits.back().instance_idx != instance_idx) {
+                        visits.push_back({instance_idx, {}, !instance_seen[instance_idx]});
+                        instance_seen[instance_idx] = true;
+                    }
+                    if (nodes[node_idx].island_idx != size_t(-1))
+                        visits.back().islands.emplace_back(nodes[node_idx].island_idx);
+                    last_visit_of_instance[instance_idx] = int(visits.size()) - 1;
+                }
+                // The trailing catch-all island has no geometry to chain by; append it to the
+                // instance's last visit.
+                for (size_t i = 0; i < instances.size(); ++i) {
+                    if (last_visit_of_instance[i] < 0)
+                        continue;
+                    InstanceVisit &last_visit = visits[size_t(last_visit_of_instance[i])];
+                    if (last_visit.islands.empty())
+                        // A visit without explicit islands already prints everything.
+                        continue;
+                    std::vector<ObjectByExtruder::Island> &islands = instances[i].object_by_extruder.islands;
+                    if (!islands.back().by_region.empty())
+                        last_visit.islands.emplace_back(islands.size() - 1);
+                }
+                cache_entry.second = std::move(visits);
             }
+            filament_plan.second = cache_entry.second;
         }
     }
 
     std::set<size_t> layer_object_label_ids;
     for (auto iter = filament_to_print_instances.begin(); iter != filament_to_print_instances.end(); ++iter) {
-        for (const InstanceToPrint &instance : iter->second) {
+        for (const InstanceToPrint &instance : iter->second.first) {
             layer_object_label_ids.insert(instance.label_object_id);
         }
     }
@@ -6231,7 +6336,7 @@ LayerResult GCode::process_layer(
 
         if (print.config().print_sequence == PrintSequence::ByLayer && m_enable_exclude_object && print.config().support_object_skip_flush.value) {
             std::vector<size_t> filament_instances_id;
-            for (InstanceToPrint &instance : filament_to_print_instances[extruder_id]) filament_instances_id.emplace_back(instance.label_object_id);
+            for (InstanceToPrint &instance : filament_to_print_instances[extruder_id].first) filament_instances_id.emplace_back(instance.label_object_id);
             m_filament_instances_code = _encode_label_ids_to_base64(filament_instances_id);
         }
 
@@ -6312,7 +6417,9 @@ LayerResult GCode::process_layer(
         if (layer_tools.has_wipe_tower && m_wipe_tower)
             m_last_processor_extrusion_role = erWipeTower;
 
-        std::vector<InstanceToPrint> &instances_to_print = filament_to_print_instances[extruder_id];
+        auto &filament_plan = filament_to_print_instances[extruder_id];
+        std::vector<InstanceToPrint>     &instances_to_print = filament_plan.first;
+        const std::vector<InstanceVisit> &instance_visits    = filament_plan.second;
 
         // We are almost ready to print. However, we must go through all the objects twice to print the overridden extrusions first (infill/perimeter wiping feature):
         std::vector<ObjectByExtruder::Island::Region> by_region_per_copy_cache;
@@ -6320,10 +6427,11 @@ LayerResult GCode::process_layer(
             if (is_anything_overridden && print_wipe_extrusions == 0)
                 gcode+="; PURGING FINISHED\n";
 
-            for (InstanceToPrint &instance_to_print : instances_to_print) {
+            for (const InstanceVisit &visit : instance_visits) {
+                InstanceToPrint &instance_to_print = instances_to_print[visit.instance_idx];
                 const auto& inst = instance_to_print.print_object.instances()[instance_to_print.instance_id];
                 const LayerToPrint &layer_to_print = layers[instance_to_print.layer_id];
-                if (print_wipe_extrusions == (is_anything_overridden ? 1 : 0)) {
+                if (visit.first_visit && print_wipe_extrusions == (is_anything_overridden ? 1 : 0)) {
                     gcode += generate_object_skirt_group(print, instance_to_print.print_object, instance_to_print.instance_id, layer_tools, layer, extruder_id);
                     gcode += generate_object_brim(print, instance_to_print.print_object, instance_to_print.instance_id, first_layer);
                 }
@@ -6376,7 +6484,7 @@ LayerResult GCode::process_layer(
                     m_avoid_crossing_perimeters.use_external_mp_once();
                 m_last_obj_copy = this_object_copy;
                 this->set_origin(unscale(offset));
-                if (instance_to_print.object_by_extruder.support != nullptr) {
+                if (visit.first_visit && instance_to_print.object_by_extruder.support != nullptr) {
                     m_layer = layers[instance_to_print.layer_id].support_layer;
                     m_object_layer_over_raft = false;
 
@@ -6410,9 +6518,42 @@ LayerResult GCode::process_layer(
                     m_layer = layer_to_print.layer();
                     m_object_layer_over_raft = object_layer_over_raft;
                 }
-                //FIXME order islands?
                 // Sequential tool path ordering of multiple parts within the same object, aka. perimeter tracking (#5511)
-                for (ObjectByExtruder::Island &island : instance_to_print.object_by_extruder.islands) {
+                // Island print order. Use the islands the tour assigned to this visit; if none,
+                // chain all islands nearest-neighbor from the current nozzle position (last_pos(),
+                // in this instance's frame after set_origin() above). Empty islands are skipped;
+                // the trailing catch-all island has no centroid to chain by and always goes last.
+                std::vector<ObjectByExtruder::Island> &islands = instance_to_print.object_by_extruder.islands;
+                std::vector<size_t> island_order = visit.islands;
+                if (island_order.empty()) {
+                    island_order.reserve(islands.size());
+                    if (layer_to_print.object_layer != nullptr && islands.size() == layer_to_print.object_layer->lslices.size() + 1) {
+                        for (size_t i = 0; i + 1 < islands.size(); ++i)
+                            if (!islands[i].by_region.empty())
+                                island_order.emplace_back(i);
+                        if (island_order.size() > 1) {
+                            Points island_centroids;
+                            island_centroids.reserve(island_order.size());
+                            for (size_t i : island_order)
+                                island_centroids.emplace_back(layer_to_print.object_layer->lslices[i].contour.centroid());
+                            const Point start_near = this->last_pos();
+                            std::vector<size_t> chain = chain_points(island_centroids, this->last_pos_defined() ? &start_near : nullptr);
+                            std::vector<size_t> ordered;
+                            ordered.reserve(island_order.size());
+                            for (size_t k : chain)
+                                ordered.emplace_back(island_order[k]);
+                            island_order = std::move(ordered);
+                        }
+                        if (!islands.back().by_region.empty())
+                            island_order.emplace_back(islands.size() - 1);
+                    } else {
+                        // Unexpected islands layout, keep the stored order.
+                        for (size_t i = 0; i < islands.size(); ++i)
+                            island_order.emplace_back(i);
+                    }
+                }
+                for (size_t island_idx : island_order) {
+                    ObjectByExtruder::Island &island = islands[island_idx];
                     const auto& by_region_specific = is_anything_overridden ? island.by_region_per_copy(by_region_per_copy_cache, static_cast<unsigned int>(instance_to_print.instance_id), extruder_id, print_wipe_extrusions != 0) : island.by_region;
                     // When starting a new object, use the external motion planner for the first travel move.
                     const Point& offset = instance_to_print.print_object.instances()[instance_to_print.instance_id].shift;
@@ -8377,29 +8518,22 @@ std::string GCode::extrusion_role_to_string_for_parser(const ExtrusionRole & rol
 }
 
 // Calculate the interpolated value for the current layer between start_value and end_value.
-// Step will create equal layers steps from first to last value.
+// Step > 0 splits the range into equal-width bands from first to last value (both inclusive).
 // Step = 0 means gradual interpolation finishing at last value.
 float GCode::interpolate_value_across_layers(float start_value, float end_value, float step) const
 {
     if (m_layer_index <= 1) {
         return start_value;
     }
-    else {
-        bool use_steps = step > 0.f;
-        if (use_steps) {
-            if (start_value > end_value) {
-                start_value += step;
-            } else {
-                end_value += step;
-            }
-        }
-        float ratio = m_layer_index / (m_layer_count - 1.f);
-        float value = start_value + ratio * (end_value - start_value);
-        if (use_steps) {
-            value = trunc(value / step) * step;
-        }
-        return value;
+    const float ratio = m_layer_index / (m_layer_count - 1.f);
+    if (step > 0.f) {
+        // Discrete equal-width bands. band is clamped to the last band so the result can't overshoot the range:
+        // at the top layer ratio * n_bands == n_bands, which would otherwise index one band past the end.
+        const int n_bands = std::lround(std::abs(end_value - start_value) / step) + 1;
+        const int band    = std::min(n_bands - 1, static_cast<int>(ratio * n_bands));
+        return start_value + (end_value >= start_value ? 1.f : -1.f) * band * step;
     }
+    return start_value + ratio * (end_value - start_value);
 }
 
 std::string encodeBase64(uint64_t value)

src/libslic3r/GCode.hpp

@@ -548,6 +548,40 @@ private:
     // Cache for custom seam enforcers/blockers for each layer.
     SeamPlacer                          m_seam_placer;
 
+    // One stop of the island-level tour: consecutive islands of a single instance. An instance
+    // can have several visits per layer when its islands are toured non-consecutively.
+    struct InstanceVisit
+    {
+        // Index into the per-filament InstanceToPrint vector.
+        size_t              instance_idx;
+        // Islands to print, in order (indices into ObjectByExtruder::islands). Empty: print all
+        // islands, ordered at extrusion time.
+        std::vector<size_t> islands;
+        // First visit of this instance this layer; skirt, brim and support are emitted here.
+        bool                first_visit;
+    };
+
+    // One node of the island-level tour, also used as cache key: identity plus quantized position.
+    struct IslandOrderNode
+    {
+        ObjectID object_id;
+        size_t   instance_id;
+        // Index into ObjectByExtruder::islands, or size_t(-1) for an instance without chainable
+        // islands (e.g. support only), which is toured as a single stop.
+        size_t   island_idx;
+        // Island centroid in G-code coordinates, quantized to 1 mm for cache stability.
+        Point    pos;
+        bool operator==(const IslandOrderNode &rhs) const {
+            return object_id == rhs.object_id && instance_id == rhs.instance_id &&
+                   island_idx == rhs.island_idx && pos == rhs.pos;
+        }
+    };
+
+    // Cache the per-filament island tour to avoid recomputing while the layer's island layout is
+    // unchanged. Key: filament_id. Value: {nodes the tour was computed from, resulting visits}.
+    std::map<unsigned int, std::pair<std::vector<IslandOrderNode>, std::vector<InstanceVisit>>>
+                                        m_ordering_cache;
+
     ExtrusionQualityEstimator m_extrusion_quality_estimator;
 
 

src/libslic3r/GCode/OrderingStrategies.cpp

@@ -0,0 +1,435 @@
+// Print-object ordering strategies: implementation.
+// Consolidates TSP post-processing, Snake, and Best-of-Strategies.
+
+#include "OrderingStrategies.hpp"
+#include "../Geometry.hpp"
+#include "../ShortestPath.hpp"
+
+#include <algorithm>
+#include <cmath>
+#include <limits>
+#include <numeric>
+#include <unordered_map>
+#include <utility>
+#include <vector>
+
+namespace Slic3r {
+
+/* ====================================================================
+ * TSP post-processing utilities
+ * ==================================================================== */
+
+bool tsp_2opt_improve(std::vector<size_t>& path, const Points& centers, int max_passes)
+{
+    size_t pn = path.size();
+    if (pn <= 2) return false;
+
+    // Pre-compute edge lengths once per pass to avoid redundant norm() calls.
+    auto recompute_edges = [&]() {
+        std::vector<double> el(pn);
+        for (size_t i = 0; i < pn; ++i) {
+            size_t ni = (i + 1) % pn;
+            el[i] = (centers[path[i]].cast<double>() - centers[path[ni]].cast<double>()).norm();
+        }
+        return el;
+    };
+    std::vector<double> el = recompute_edges();
+
+    // Pre-compute squared edge lengths for early rejection in the inner loop.
+    auto recompute_edges_sq = [&]() {
+        std::vector<double> elsq(pn);
+        for (size_t i = 0; i < pn; ++i) {
+            size_t ni = (i + 1) % pn;
+            elsq[i] = (centers[path[i]].cast<double>() - centers[path[ni]].cast<double>()).squaredNorm();
+        }
+        return elsq;
+    };
+    std::vector<double> elsq = recompute_edges_sq();
+
+    bool improved = false;
+    for (int pass = 0; max_passes <= 0 || pass < max_passes; ++pass) {
+        size_t best_i = pn, best_j = pn;
+        double best_gain = 0;
+
+        for (size_t i = 0; i < pn; ++i) {
+            const Vec2d& pi   = centers[path[i]].cast<double>();
+            const Vec2d& p_in = centers[path[(i + 1) % pn]].cast<double>();
+            double d_i = el[i];
+            double d_i_sq = elsq[i];
+
+            for (size_t j = i + 2; j < pn; ++j) {
+                size_t j_next = (j + 1) % pn;
+                // Skip the swap that would reverse the entire cycle (removes both
+                // edges (0,1) and (pn-1,0), equivalent to traversing the cycle backwards).
+                if (i == 0 && j_next == 0) continue;
+
+                const Vec2d& pj   = centers[path[j]].cast<double>();
+                const Vec2d& p_jn = centers[path[j_next]].cast<double>();
+                double d_j = el[j];
+
+                // Early rejection using squared distances (avoids 2 sqrt calls).
+                double new_a_sq = (pj - pi).squaredNorm();
+                double new_b_sq = (p_jn - p_in).squaredNorm();
+                if (new_a_sq >= d_i_sq && new_b_sq >= elsq[j]) continue;
+
+                double new_a = std::sqrt(new_a_sq);
+                double new_b = std::sqrt(new_b_sq);
+                double gain = d_i + d_j - new_a - new_b;
+
+                if (gain > best_gain) {
+                    best_gain = gain;
+                    best_i = i; best_j = j;
+                }
+            }
+        }
+
+        if (best_i == pn) break;
+        improved = true;
+        // Reverse the best swap segment
+        std::reverse(path.begin() + best_i + 1, path.begin() + best_j + 1);
+
+        // Recompute edge lengths after reversal
+        el = recompute_edges();
+        elsq = recompute_edges_sq();
+    }
+    return improved;
+}
+
+// Fast bounding-box overlap test (rejects most non-intersecting pairs).
+static inline bool bboxes_overlap(const Point& a, const Point& b, const Point& c, const Point& d)
+{
+    return !(std::max(a.x(), b.x()) < std::min(c.x(), d.x()) ||
+             std::max(c.x(), d.x()) < std::min(a.x(), b.x()) ||
+             std::max(a.y(), b.y()) < std::min(c.y(), d.y()) ||
+             std::max(c.y(), d.y()) < std::min(a.y(), b.y()));
+}
+
+bool tsp_remove_crossings(std::vector<size_t>& path, const Points& centers)
+{
+    size_t pn = path.size();
+    if (pn <= 3) return false;
+
+    // Treat path as a cycle: include the closing edge (pn-1 -> 0), consistent with the other
+    // TSP helpers (2-opt, closing-edge rotation) that operate on the full cycle.
+    size_t n_edges = pn;
+
+    // Scan for first crossing; returns {i, j} or {npos, npos} if none.
+    auto find_crossing = [&]() -> std::pair<size_t, size_t> {
+        for (size_t i = 0; i < n_edges; ++i) {
+            const Point& ai = centers[path[i]];
+            const Point& bi = centers[path[(i + 1) % pn]];
+
+            for (size_t j = i + 2; j < n_edges; ++j) {
+                // Skip the (0, pn-1) pair: edges (0,1) and (pn-1,0) share node 0.
+                if (i == 0 && j == pn - 1) continue;
+
+                const Point& aj = centers[path[j]];
+                const Point& bj = centers[path[(j + 1) % pn]];
+
+                if (!bboxes_overlap(ai, bi, aj, bj)) continue;
+                if (Geometry::segments_intersect(ai, bi, aj, bj))
+                    return {i, j};
+            }
+        }
+        return {std::numeric_limits<size_t>::max(), std::numeric_limits<size_t>::max()};
+    };
+
+    // Process crossings one at a time: find first, reverse it, restart scan.
+    // Cap iterations to prevent infinite loops on collinear/overlapping segments.
+    int max_iters = static_cast<int>(pn * pn);
+    bool improved = false;
+    while (max_iters-- > 0) {
+        auto [ci, cj] = find_crossing();
+        if (ci == std::numeric_limits<size_t>::max()) break;
+        improved = true;
+        std::reverse(path.begin() + ci + 1, path.begin() + cj + 1);
+    }
+    return improved;
+}
+
+void tsp_rotate_minimize_closing(std::vector<size_t>& path, const Points& centers)
+{
+    size_t pn = path.size();
+    size_t best_start = 0;
+    double best_closing2 = std::numeric_limits<double>::max();
+    for (size_t start = 0; start < pn; ++start) {
+        size_t last = (start + pn - 1) % pn;
+        double d2 = (centers[path[start]].cast<double>() - centers[path[last]].cast<double>()).squaredNorm();
+        if (d2 < best_closing2) { best_closing2 = d2; best_start = start; }
+    }
+    std::rotate(path.begin(), path.begin() + best_start, path.end());
+}
+
+/* ====================================================================
+ * Snake ordering
+ * ==================================================================== */
+
+struct SnakeRow { double avg_y; std::vector<size_t> indices; };
+
+// --- Row threshold computation ---
+// Extract unique Y values and use the median gap between them to determine
+// the row threshold.
+static double compute_row_threshold(const std::vector<double>& sorted_ys,
+                                    double y_min, double y_max,
+                                    size_t n,
+                                    double fraction_of_y_range,
+                                    double min_threshold_um)
+{
+    constexpr double MIN_GAP_FILTER = 1.0;  // ignore sub-micron gaps (coord_t = 1/100mm)
+
+    // Extract unique Y values
+    std::vector<double> unique_ys;
+    unique_ys.reserve(sorted_ys.size());
+    unique_ys.push_back(sorted_ys[0]);
+    for (size_t i = 1; i < sorted_ys.size(); ++i) {
+        if (sorted_ys[i] - sorted_ys[i - 1] > MIN_GAP_FILTER)
+            unique_ys.push_back(sorted_ys[i]);
+    }
+
+    double fallback_threshold = (y_max - y_min) * fraction_of_y_range;
+    if (unique_ys.size() <= 1) {
+        return std::max(fallback_threshold, min_threshold_um);
+    }
+
+    // Compute gaps between consecutive unique Y values
+    std::vector<double> gaps;
+    gaps.reserve(unique_ys.size() - 1);
+    for (size_t i = 1; i < unique_ys.size(); ++i)
+        gaps.push_back(unique_ys[i] - unique_ys[i - 1]);
+
+    if (gaps.empty()) {
+        return std::max(fallback_threshold, min_threshold_um);
+    }
+
+    // Sort gaps to find the median
+    std::sort(gaps.begin(), gaps.end());
+    double median_gap = gaps[gaps.size() / 2];
+    double min_gap = gaps.front();
+
+    // Threshold: half the gap between consecutive unique Y values.
+    double threshold = (median_gap < min_gap * 1.5) ? min_gap * 0.5 : median_gap * 0.5;
+
+    bool has_row_structure;
+    if (unique_ys.size() * 2 <= n) {
+        has_row_structure = true;
+    } else {
+        // Single-column or sparse: uniform gaps indicate a deliberate grid
+        double max_gap = *std::max_element(gaps.begin(), gaps.end());
+        has_row_structure = (max_gap < min_gap * 2.0);
+    }
+
+    if (has_row_structure) {
+        // For grid-like data, use the gap-based threshold directly.
+        return threshold;
+    }
+
+    return std::max(fallback_threshold, min_threshold_um);
+}
+
+// --- Row grouping ---
+// Bin points into rows by quantising Y / threshold
+static std::vector<SnakeRow> group_into_rows(const Points& centers, double row_threshold)
+{
+    size_t n = centers.size();
+    std::unordered_map<int64_t, std::vector<size_t>> row_map;
+    for (size_t i = 0; i < n; ++i) {
+        int64_t y_key = static_cast<int64_t>(std::floor(static_cast<double>(centers[i].y()) / row_threshold));
+        row_map[y_key].push_back(i);
+    }
+
+    std::vector<SnakeRow> rows;
+    rows.reserve(row_map.size());
+    for (auto& [key, indices] : row_map) {
+        double avg_y = std::accumulate(indices.begin(), indices.end(), 0.0,
+            [&](double acc, size_t idx) { return acc + static_cast<double>(centers[idx].y()); })
+            / indices.size();
+        rows.push_back({avg_y, std::move(indices)});
+    }
+
+    std::sort(rows.begin(), rows.end(),
+              [](const SnakeRow& a, const SnakeRow& b) { return a.avg_y < b.avg_y; });
+
+    return rows;
+}
+
+// Sort each row by X and greedily pick the direction (left->right or right->left)
+// that minimises the transition distance from the previous row's endpoint.
+static std::vector<size_t> build_serpentine_path(const Points& centers,
+                                                  std::vector<SnakeRow>& rows)
+{
+    std::vector<size_t> path;
+    path.reserve(centers.size());
+
+    for (size_t ri = 0; ri < rows.size(); ++ri) {
+        auto& row = rows[ri].indices;
+        std::sort(row.begin(), row.end(),
+                  [&](size_t a, size_t b) { return centers[a].x() < centers[b].x(); });
+
+        if (ri == 0) {
+            path.insert(path.end(), row.begin(), row.end());
+        } else {
+            const Point& prev_end = centers[path.back()];
+            double dist_to_left  = (prev_end.cast<double>() - centers[row.front()].cast<double>()).squaredNorm();
+            double dist_to_right = (prev_end.cast<double>() - centers[row.back()].cast<double>()).squaredNorm();
+
+            if (dist_to_left <= dist_to_right)
+                path.insert(path.end(), row.begin(), row.end());
+            else
+                path.insert(path.end(), row.rbegin(), row.rend());
+        }
+    }
+
+    return path;
+}
+
+// Row-based serpentine traversal: detect rows, bin points, snake through them.
+static std::vector<size_t> row_serpentine_path(const Points& centers,
+                                                double fraction_of_y_range = 0.02,
+                                                double min_threshold_um = 1e4)
+{
+    if (centers.empty()) return {};
+
+    size_t n = centers.size();
+
+    // Collect and sort Y coordinates.
+    std::vector<double> sorted_ys;
+    sorted_ys.reserve(n);
+    for (const auto& p : centers) sorted_ys.push_back(static_cast<double>(p.y()));
+    std::sort(sorted_ys.begin(), sorted_ys.end());
+
+    auto [ymin, ymax] = std::minmax_element(sorted_ys.begin(), sorted_ys.end());
+    double y_min = *ymin, y_max = *ymax;
+
+    double row_threshold = compute_row_threshold(sorted_ys, y_min, y_max, n,
+                                                  fraction_of_y_range, min_threshold_um);
+
+    auto rows = group_into_rows(centers, row_threshold);
+    return build_serpentine_path(centers, rows);
+}
+
+std::vector<size_t> snake_core(const Points& centers)
+{
+    if (centers.empty()) return {};
+
+    std::vector<size_t> path = row_serpentine_path(centers);
+
+    for (int iter = 0; iter < 3; ++iter) {
+        bool improved = tsp_2opt_improve(path, centers);
+        improved |= tsp_remove_crossings(path, centers);
+        if (!improved) break;
+    }
+
+    return path;
+}
+
+std::vector<const PrintInstance*> chain_print_object_instances_snake(const std::vector<const PrintObject*>& print_objects, const Point* start_near)
+{
+    return chain_instances_with_core(print_objects, start_near, snake_core);
+}
+
+std::vector<const PrintInstance*> chain_print_object_instances_snake(const Print& print)
+{
+    return chain_print_object_instances_snake(print.objects().vector(), nullptr);
+}
+
+/* ====================================================================
+ * Best-of-strategies meta-strategy
+ * ==================================================================== */
+
+std::vector<const PrintInstance*> chain_print_object_instances_best_of(const std::vector<const PrintObject*>& print_objects, const Point* start_near)
+{
+    if (print_objects.empty())
+        return {};
+
+    // Run all strategies.
+    std::vector<std::vector<const PrintInstance*>> candidates;
+    candidates.push_back(chain_print_object_instances(print_objects, start_near));
+    candidates.push_back(chain_print_object_instances_snake(print_objects, start_near));
+
+    // Compute metrics for each candidate.
+    struct Candidate { double total_len; double max_edge; };
+    std::vector<Candidate> metrics;
+    metrics.reserve(candidates.size());
+
+    for (size_t i = 0; i < candidates.size(); ++i) {
+        double total = 0.0;
+        double mx = 0.0;
+        for (size_t j = 0; j < candidates[i].size(); ++j) {
+            size_t k = (j + 1) % candidates[i].size();
+            double d = (candidates[i][j]->shift.cast<double>() - candidates[i][k]->shift.cast<double>()).norm();
+            total += d;
+            if (d > mx) mx = d;
+        }
+        metrics.push_back({total, mx});
+    }
+
+    // Pick shortest total path; tiebreak on smallest max edge.
+    auto best_it = std::min_element(metrics.begin(), metrics.end(),
+        [](const Candidate& a, const Candidate& b) {
+            return a.total_len < b.total_len ||
+                   (a.total_len == b.total_len && a.max_edge < b.max_edge);
+        });
+    size_t best = static_cast<size_t>(std::distance(metrics.begin(), best_it));
+
+    return candidates[best];
+}
+
+std::vector<const PrintInstance*> chain_print_object_instances_best_of(const Print& print)
+{
+    return chain_print_object_instances_best_of(print.objects().vector(), nullptr);
+}
+
+/* ====================================================================
+ * Island-level ordering entry point
+ * ==================================================================== */
+
+std::vector<size_t> order_points_with_strategy(const Points& points, PrintOrder print_order, const Point* start_near)
+{
+    if (points.empty())
+        return {};
+
+    if (print_order != PrintOrder::Snake && print_order != PrintOrder::BestOfStrategies)
+        // Nearest neighbor + post-processing; honours start_near natively.
+        return chain_points_with_postprocessing(points, start_near);
+
+    auto run_snake = [&points, start_near]() {
+        std::vector<size_t> path = snake_core(points);
+        if (start_near != nullptr && !path.empty()) {
+            // Start the cycle at the point closest to start_near.
+            size_t best_start = 0;
+            double best_d2 = std::numeric_limits<double>::max();
+            for (size_t k = 0; k < points.size(); ++k) {
+                double d2 = (points[k].cast<double>() - start_near->cast<double>()).squaredNorm();
+                if (d2 < best_d2) { best_d2 = d2; best_start = k; }
+            }
+            auto it = std::find(path.begin(), path.end(), best_start);
+            if (it != path.begin() && it != path.end())
+                std::rotate(path.begin(), it, path.end());
+        } else {
+            tsp_rotate_minimize_closing(path, points);
+        }
+        return path;
+    };
+
+    if (print_order == PrintOrder::Snake)
+        return run_snake();
+
+    // Best-of: pick the shortest total cycle; tiebreak on smallest max edge.
+    std::vector<std::vector<size_t>> candidates;
+    candidates.emplace_back(chain_points_with_postprocessing(points, start_near));
+    candidates.emplace_back(run_snake());
+
+    size_t best      = 0;
+    double best_len  = std::numeric_limits<double>::max();
+    double best_edge = std::numeric_limits<double>::max();
+    for (size_t i = 0; i < candidates.size(); ++i) {
+        double len  = tsp_cycle_path_length(candidates[i], points);
+        double edge = tsp_max_edge_length(candidates[i], points);
+        if (len < best_len || (len == best_len && edge < best_edge)) {
+            best_len = len; best_edge = edge; best = i;
+        }
+    }
+    return candidates[best];
+}
+
+} // namespace Slic3r

src/libslic3r/GCode/OrderingStrategies.hpp

@@ -0,0 +1,148 @@
+// Print-object ordering strategies and shared TSP post-processing utilities.
+
+#ifndef slic3r_OrderingStrategies_hpp_
+#define slic3r_OrderingStrategies_hpp_
+
+#include "../libslic3r.h"
+#include "../Point.hpp"
+
+#ifndef SLIC3R_TEST_HARNESS
+#include "../Print.hpp"
+#endif
+
+#include <algorithm>
+#include <limits>
+#include <utility>
+#include <vector>
+
+namespace Slic3r {
+
+// --- Path improvement (operate on index vectors into `centers`) ---
+
+// 2-opt improvement: reverses segments that reduce total cycle path length.
+// Returns true if any improvement was made.
+bool tsp_2opt_improve(std::vector<size_t>& path, const Points& centers, int max_passes = 10);
+
+// Crossing removal: reverse any segment pair whose edges geometrically cross.
+// Returns true if any crossing was removed.
+bool tsp_remove_crossings(std::vector<size_t>& path, const Points& centers);
+
+// Rotate the cycle so the closing edge (last -> first) is minimized.
+void tsp_rotate_minimize_closing(std::vector<size_t>& path, const Points& centers);
+
+// Total Euclidean path length of a cycle (including closing edge).
+inline double tsp_cycle_path_length(const std::vector<size_t>& path, const Points& centers)
+{
+    if (path.size() < 2) return 0.0;
+    double total = 0.0;
+    for (size_t i = 0; i < path.size(); ++i) {
+        size_t next = (i + 1) % path.size();
+        total += (centers[path[i]].cast<double>() - centers[path[next]].cast<double>()).norm();
+    }
+    return total;
+}
+
+// Maximum edge length of a cycle (including closing edge).
+inline double tsp_max_edge_length(const std::vector<size_t>& path, const Points& centers)
+{
+    if (path.size() < 2) return 0.0;
+    double mx = 0.0;
+    for (size_t i = 0; i < path.size(); ++i) {
+        size_t next = (i + 1) % path.size();
+        double d = (centers[path[i]].cast<double>() - centers[path[next]].cast<double>()).norm();
+        if (d > mx) mx = d;
+    }
+    return mx;
+}
+
+
+
+#ifndef SLIC3R_TEST_HARNESS
+
+// --- Wrapper boilerplate ---
+
+// Collect instance centers from PrintObjects, optionally pre-rotate to honour
+// start_near, call a core algorithm, and map the result back to PrintInstance*.
+template<typename CoreFn>
+std::vector<const PrintInstance*> chain_instances_with_core(
+    const std::vector<const PrintObject*>& print_objects,
+    const Point* start_near,
+    CoreFn&& core_fn)
+{
+    Points instance_centers;
+    std::vector<std::pair<size_t, size_t>> instances;
+    for (size_t i = 0; i < print_objects.size(); ++i) {
+        const PrintObject& object = *print_objects[i];
+        for (size_t j = 0; j < object.instances().size(); ++j) {
+            instance_centers.emplace_back(object.instances()[j].shift);
+            instances.emplace_back(i, j);
+        }
+    }
+
+    if (instance_centers.empty()) return {};
+
+    // If start_near is provided, pre-rotate so closest point is first.
+    if (start_near != nullptr) {
+        size_t best_start = 0;
+        double best_d2 = std::numeric_limits<double>::max();
+        for (size_t k = 0; k < instance_centers.size(); ++k) {
+            double d2 = (instance_centers[k].cast<double>() - start_near->cast<double>()).squaredNorm();
+            if (d2 < best_d2) { best_d2 = d2; best_start = k; }
+        }
+        std::rotate(instance_centers.begin(), instance_centers.begin() + best_start, instance_centers.end());
+        std::rotate(instances.begin(), instances.begin() + best_start, instances.end());
+    }
+
+    auto path = core_fn(instance_centers);
+
+    // Rotate the cycle so the first element is the best starting point.
+    // When start_near is provided, pick the point closest to it (preserving
+    // the pre-rotation). Otherwise minimise the closing edge.
+    if (start_near != nullptr && !path.empty()) {
+        // Pre-rotation already put the closest point at index 0.
+        // Find where index 0 appears in the path and rotate it to the front.
+        auto it = std::find(path.begin(), path.end(), size_t(0));
+        if (it != path.begin())
+            std::rotate(path.begin(), it, path.end());
+    } else {
+        tsp_rotate_minimize_closing(path, instance_centers);
+    }
+
+    std::vector<const PrintInstance*> out;
+    out.reserve(path.size());
+    for (size_t step : path) {
+        out.emplace_back(&print_objects[instances[step].first]->instances()[instances[step].second]);
+    }
+    return out;
+}
+
+#endif // SLIC3R_TEST_HARNESS
+
+// --- Core algorithms (operate on raw Points, return index permutations) ---
+
+// Snake ordering: row grouping + serpentine traversal + post-processing.
+std::vector<size_t> snake_core(const Points& centers);
+
+#ifndef SLIC3R_TEST_HARNESS
+
+// --- Production wrappers ---
+
+// Snake ordering.
+std::vector<const PrintInstance*> chain_print_object_instances_snake(const std::vector<const PrintObject*>& print_objects, const Point* start_near);
+std::vector<const PrintInstance*> chain_print_object_instances_snake(const Print& print);
+
+// Best-of-strategies: run all strategies and return the shortest result.
+// Primary: shortest total path; secondary tiebreaker: smallest max edge.
+std::vector<const PrintInstance*> chain_print_object_instances_best_of(const std::vector<const PrintObject*>& print_objects, const Point* start_near);
+std::vector<const PrintInstance*> chain_print_object_instances_best_of(const Print& print);
+
+// Order raw points with the selected strategy, returning an index permutation. Island-level
+// counterpart of the chain_print_object_instances_* helpers. The returned cycle starts at the
+// point closest to start_near; orders without a dedicated strategy use nearest-neighbor chaining.
+std::vector<size_t> order_points_with_strategy(const Points& points, PrintOrder print_order, const Point* start_near);
+
+#endif // SLIC3R_TEST_HARNESS
+
+} // namespace Slic3r
+
+#endif /* slic3r_OrderingStrategies_hpp_ */

src/libslic3r/PerimeterGenerator.cpp

@@ -360,6 +360,14 @@ static ClipperLib_Z::Paths clip_extrusion(const ClipperLib_Z::Path& subject, con
     return clipped_paths;
 }
 
+static double clipper_z_path_length(const ClipperLib_Z::Path &path)
+{
+    double len = 0.;
+    for (size_t i = 1; i < path.size(); ++ i)
+        len += (Vec2d(double(path[i].x()), double(path[i].y())) - Vec2d(double(path[i - 1].x()), double(path[i - 1].y()))).norm();
+    return len;
+}
+
 struct PerimeterGeneratorArachneExtrusion
 {
     Arachne::ExtrusionLine* extrusion = nullptr;
@@ -571,17 +579,156 @@ static ExtrusionEntityCollection traverse_extrusions(const PerimeterGenerator& p
     return extrusion_coll;
 }
 
-// ORCA: only_one_wall_top detects the top as "slice − upper", so a feature rising from the middle of a
-// top surface becomes an enclosed hole that gets ringed with extra inner walls. Fill those holes back
-// into the top. Only holes that are both covered by the upper layer (excludes bridges) and backed by
-// solid material (excludes voids) are filled.
-static ExPolygons fill_enclosed_top_feature_holes(const ExPolygons &top, const Polygons &covered_by_upper, const ExPolygons &solid)
+// ORCA: only_one_wall_top acts on top surfaces, so without a top shell there is nothing for it to act on: zero top
+// shell layers retype the top surfaces as internal, see LayerRegion::prepare_fill_surfaces(). A 0% top surface
+// density does leave a top surface - just an unfilled one - so it does not disable the feature.
+// ConfigManipulation::toggle_print_fff_options() hides the option under the same condition, so a profile that left
+// it enabled does not act behind a hidden checkbox.
+static bool has_top_shell_layers(const PrintRegionConfig &config)
 {
-    ExPolygons filled = top;
-    for (ExPolygon &ex : filled)
-        ex.holes.clear();
-    const ExPolygons feature_holes = intersection_ex(intersection_ex(diff_ex(filled, top), covered_by_upper), solid);
-    return feature_holes.empty() ? top : union_ex(top, feature_holes);
+    return config.top_shell_layers.value > 0;
+}
+
+// ORCA: only_one_wall_first_layer thins the first layer to a single wall, the bottom counterpart of the above and
+// gated the same way: zero bottom shell layers retype the bottom surfaces as internal, so that wall would ring
+// sparse infill on the bed. The bottom surface density plays no part - an unfilled bottom surface is still a bottom
+// surface, exactly as for the top - and it cannot reach zero anyway, being capped at a 10% minimum.
+static bool has_bottom_shell_layers(const PrintRegionConfig &config)
+{
+    return config.bottom_shell_layers.value > 0;
+}
+
+// ORCA: the inner walls are only given up when a top fill takes their space, and it has to actually reach it -
+// a 0% top surface density leaves no fill at all, and without top_surface_expansion the fill never grows over
+// them. Either way the original generation is kept (re-onion the not-top region), which is what users of
+// only_one_wall_top alone have always got.
+static bool top_fill_replaces_inner_walls(const PrintRegionConfig &config)
+{
+    return has_top_shell_layers(config) && config.top_surface_density.value > 0 && config.top_surface_expansion.value > 0;
+}
+
+// ORCA: only_one_wall_top - cheap per-vertex classification of a wall against the top surface. Only Partial
+// needs the geometry clipped or measured; a segment crossing the top with no vertex inside is rare enough to ignore.
+enum class TopOverlap { None, Partial, Full };
+
+static bool point_over_top(const Point &p, const ExPolygons &top_region, const BoundingBox &top_region_bbox)
+{
+    if (! top_region_bbox.contains(p))
+        return false;
+    for (const ExPolygon &ex : top_region)
+        if (ex.contains(p, false))
+            return true;
+    return false;
+}
+
+static TopOverlap classify_over_top(const Points &pts, const ExPolygons &top_region, const BoundingBox &top_region_bbox)
+{
+    size_t inside = 0;
+    for (const Point &p : pts)
+        if (point_over_top(p, top_region, top_region_bbox))
+            ++ inside;
+    return inside == 0 ? TopOverlap::None : inside == pts.size() ? TopOverlap::Full : TopOverlap::Partial;
+}
+
+static TopOverlap classify_over_top(const Arachne::ExtrusionLine &el, const ExPolygons &top_region, const BoundingBox &top_region_bbox)
+{
+    size_t inside = 0;
+    for (const Arachne::ExtrusionJunction &j : el.junctions)
+        if (point_over_top(j.p, top_region, top_region_bbox))
+            ++ inside;
+    return inside == 0 ? TopOverlap::None : inside == el.junctions.size() ? TopOverlap::Full : TopOverlap::Partial;
+}
+
+// ORCA: only_one_wall_top for Arachne - cut out of the already generated inner walls the parts running over the top
+// surface, so geometry that continues upward keeps its walls. A wall too short over the top to be worth slitting open
+// is left whole, its footprint reported in kept_over_top for the caller to withhold from the top fill.
+static void clip_inner_walls_over_top(std::vector<Arachne::VariableWidthLines> &inner_perimeters, const ExPolygons &top_region, coord_t perimeter_width, Polygons &kept_over_top)
+{
+    const BoundingBox top_region_bbox = get_extents(top_region).inflated(SCALED_EPSILON);
+    auto covered_by = [](const Arachne::ExtrusionLine &el) {
+        Polyline centerline;
+        centerline.points.reserve(el.junctions.size());
+        coord_t width = 0;
+        for (const Arachne::ExtrusionJunction &j : el.junctions) {
+            centerline.points.emplace_back(j.p);
+            width = std::max(width, j.w);
+        }
+        return offset(centerline, float(width) / 2.f);
+    };
+    // Pull the cut back by half a wall width: the clip severs the centerline, but the bead's rounded end
+    // extends half a width past its endpoint and would otherwise overlap the top fill.
+    ClipperLib_Z::Paths top_paths_z;
+    for (const Polygon &poly : to_polygons(offset_ex(top_region, float(perimeter_width) / 2.f))) {
+        top_paths_z.emplace_back();
+        ClipperLib_Z::Path &out = top_paths_z.back();
+        out.reserve(poly.points.size());
+        for (const Point &pt : poly.points)
+            out.emplace_back(pt.x(), pt.y(), 0);
+    }
+    for (Arachne::VariableWidthLines &inner_perimeter : inner_perimeters) {
+        Arachne::VariableWidthLines kept;
+        kept.reserve(inner_perimeter.size());
+        for (Arachne::ExtrusionLine &el : inner_perimeter) {
+            if (el.empty())
+                continue;
+            const TopOverlap overlap = classify_over_top(el, top_region, top_region_bbox);
+            if (overlap == TopOverlap::None) {
+                kept.emplace_back(std::move(el));
+                continue;
+            }
+            if (overlap == TopOverlap::Full)
+                continue; // the clip below would return nothing anyway
+            ClipperLib_Z::Path subject;
+            subject.reserve(el.size());
+            for (const Arachne::ExtrusionJunction &j : el.junctions)
+                subject.emplace_back(j.p.x(), j.p.y(), j.w);
+            ClipperLib_Z::Paths pieces = clip_extrusion(subject, top_paths_z, ClipperLib_Z::ctDifference);
+
+            // Clipper treats the subject as an open polyline, so it also cuts a closed loop at its (arbitrary)
+            // start vertex and may reverse pieces. Stitch pieces sharing an endpoint back together.
+            auto same_pt = [](const ClipperLib_Z::IntPoint &p, const ClipperLib_Z::IntPoint &q) {
+                return std::abs(p.x() - q.x()) <= SCALED_EPSILON && std::abs(p.y() - q.y()) <= SCALED_EPSILON;
+            };
+            for (size_t i = 0; i < pieces.size(); ++ i) {
+                for (size_t j = i + 1; j < pieces.size();) {
+                    ClipperLib_Z::Path &a = pieces[i];
+                    ClipperLib_Z::Path &b = pieces[j];
+                    if (same_pt(a.front(), b.front()) || same_pt(a.front(), b.back()))
+                        std::reverse(a.begin(), a.end());
+                    if (same_pt(a.back(), b.back()))
+                        std::reverse(b.begin(), b.end());
+                    if (same_pt(a.back(), b.front())) {
+                        a.insert(a.end(), b.begin() + 1, b.end());
+                        pieces.erase(pieces.begin() + j);
+                        j = i + 1; // the merged path has new endpoints, restart the scan
+                    } else
+                        ++ j;
+                }
+            }
+
+            // If the clip removed next to nothing, keep the loop untouched instead of slitting it open. The
+            // half-width pull-back above already costs about one width per crossing, hence two widths.
+            double kept_length = 0.;
+            for (const ClipperLib_Z::Path &path : pieces)
+                kept_length += clipper_z_path_length(path);
+            if (clipper_z_path_length(subject) - kept_length < 2. * double(perimeter_width)) {
+                append(kept_over_top, covered_by(el));
+                kept.emplace_back(std::move(el));
+                continue;
+            }
+
+            for (const ClipperLib_Z::Path &path : pieces) {
+                Arachne::ExtrusionLine clipped(el.inset_idx, el.is_odd);
+                clipped.junctions.reserve(path.size());
+                for (const ClipperLib_Z::IntPoint &pt : path)
+                    clipped.junctions.emplace_back(Point(pt.x(), pt.y()), coord_t(pt.z()), el.inset_idx);
+                // Discard tiny leftovers that would print as zits.
+                if (clipped.size() >= 2 && clipped.getLength() >= perimeter_width)
+                    kept.emplace_back(std::move(clipped));
+            }
+        }
+        inner_perimeter = std::move(kept);
+    }
 }
 
 void PerimeterGenerator::split_top_surfaces(const ExPolygons &orig_polygons, ExPolygons &top_fills,
@@ -649,7 +796,6 @@ void PerimeterGenerator::split_top_surfaces(const ExPolygons &orig_polygons, ExP
     ExPolygons delete_bridge = diff_ex(orig_polygons, bridge_checker, ApplySafetyOffset::Yes);
 
     ExPolygons top_polygons = diff_ex(delete_bridge, upper_polygons_series_clipped, ApplySafetyOffset::Yes);
-    top_polygons = fill_enclosed_top_feature_holes(top_polygons, upper_polygons_series_clipped, orig_polygons);
 
     // get the not-top surface, from the "real top" but enlarged by external_infill_margin (and the
     // min_width_top_surface we removed a bit before)
@@ -1234,6 +1380,11 @@ void PerimeterGenerator::process_classic()
     for (const Surface &surface : all_surfaces)
         surface_exp.push_back(surface.expolygon);
     std::vector<size_t> surface_order = chain_expolygons(surface_exp);
+    // ORCA: neither one-wall option has a surface to act on without the shell behind it, see
+    // has_top_shell_layers() / has_bottom_shell_layers(). Gated here so every use below - including the
+    // topmost and first layers - sees the same answer.
+    const bool only_one_wall_top         = this->config->only_one_wall_top && has_top_shell_layers(*this->config);
+    const bool only_one_wall_first_layer = this->config->only_one_wall_first_layer && has_bottom_shell_layers(*this->config);
     for (size_t order_idx = 0; order_idx < surface_order.size(); order_idx++) {
         const Surface &surface = all_surfaces[surface_order[order_idx]];
         // detect how many perimeters must be generated for this island
@@ -1241,16 +1392,23 @@ void PerimeterGenerator::process_classic()
         int sparse_infill_density = this->config->sparse_infill_density.value;
         if (this->config->alternate_extra_wall && this->layer_id % 2 == 1 && !m_spiral_vase && sparse_infill_density > 0) // add alternating extra wall
             loop_number++;
-        if (this->layer_id == object_config->raft_layers && this->config->only_one_wall_first_layer)
+        if (this->layer_id == object_config->raft_layers && only_one_wall_first_layer)
             loop_number = 0;
         // Set the topmost layer to be one wall
-        if (loop_number > 0 && config->only_one_wall_top && this->upper_slices == nullptr)
+        if (loop_number > 0 && only_one_wall_top && this->upper_slices == nullptr)
             loop_number = 0;
 
         ExPolygons last        = union_ex(surface.expolygon.simplify_p(surface_simplify_resolution));
         ExPolygons gaps;
         ExPolygons top_fills;
         ExPolygons fill_clip;
+        // ORCA: only_one_wall_top, all empty unless this island has a top surface on this layer. See the
+        // post-onion reduction below: the region to keep clear of inner walls, the space freed by the dropped
+        // walls (goes to infill, not left as a void) and the space held by the kept ones (withheld from the fill).
+        ExPolygons one_wall_top_region;
+        ExPolygons one_wall_top_reclaimed;
+        Polygons   one_wall_top_kept_bands;
+        bool       apply_one_wall_top = false;
         if (loop_number >= 0) {
             // In case no perimeters are to be generated, loop_number will equal to -1.
             std::vector<PerimeterGeneratorLoops> contours(loop_number+1);    // depth => loops
@@ -1389,8 +1547,19 @@ void PerimeterGenerator::process_classic()
 
                 //BBS: refer to superslicer
                 //store surface for top infill if only_one_wall_top
-                if (i == 0 && i!=loop_number && config->only_one_wall_top && !surface.is_bridge() && this->upper_slices != NULL) {
-                    this->split_top_surfaces(last, top_fills, last, fill_clip);
+                if (i == 0 && i!=loop_number && only_one_wall_top && !surface.is_bridge() && this->upper_slices != NULL) {
+                    if (top_fill_replaces_inner_walls(*this->config)) {
+                        // ORCA: take the top fill and the keep-out region but leave `last` as the real geometry,
+                        // so the onion follows it and the walls over the top are reduced in one step below.
+                        ExPolygons non_top_polygons;
+                        this->split_top_surfaces(last, top_fills, non_top_polygons, fill_clip);
+                        apply_one_wall_top = !top_fills.empty();
+                        if (apply_one_wall_top)
+                            one_wall_top_region = diff_ex(last, non_top_polygons);
+                    } else {
+                        // Onion the not-top region only, so the remaining walls stop at the top boundary.
+                        this->split_top_surfaces(last, top_fills, last, fill_clip);
+                    }
                 }
 
                 if (i == loop_number && (! has_gap_fill || this->config->sparse_infill_density.value == 0)) {
@@ -1400,6 +1569,46 @@ void PerimeterGenerator::process_classic()
                 }
             }
 
+            // ORCA: only_one_wall_top reduction - drop the inner walls (depth > 0) running over the top surface and
+            // take that space back from the gaps, leaving the top with the outer wall and the top infill. Classic
+            // perimeters are closed loops, so a wall can only be kept or dropped whole; one that merely grazes the
+            // top (same tolerance as the Arachne clip) is kept and withheld from the top fill instead.
+            if (apply_one_wall_top) {
+                const BoundingBox top_region_bbox   = get_extents(one_wall_top_region).inflated(SCALED_EPSILON);
+                const double      grazing_tolerance = 2. * double(perimeter_width);
+                // The band a wall covers, taken around its centerline so the orientation of holes does not matter.
+                auto wall_band = [perimeter_spacing](const Polygon &poly) {
+                    Polygon centerline = poly;
+                    centerline.make_counter_clockwise();
+                    return diff(offset(centerline, float(perimeter_spacing) / 2.f),
+                                offset(centerline, -float(perimeter_spacing) / 2.f));
+                };
+                Polygons dropped_wall_bands;
+                auto reduce_over_top = [&](PerimeterGeneratorLoops &loops) {
+                    loops.erase(std::remove_if(loops.begin(), loops.end(), [&](const PerimeterGeneratorLoop &loop) {
+                        const TopOverlap overlap = classify_over_top(loop.polygon.points, one_wall_top_region, top_region_bbox);
+                        if (overlap == TopOverlap::None)
+                            return false;
+                        // Only a wall straddling the boundary is worth measuring; a wall wholly over the top goes.
+                        if (overlap == TopOverlap::Partial &&
+                            total_length(intersection_pl(Polylines{ loop.polygon.split_at_first_point() }, one_wall_top_region)) < grazing_tolerance) {
+                            append(one_wall_top_kept_bands, wall_band(loop.polygon));
+                            return false;
+                        }
+                        append(dropped_wall_bands, wall_band(loop.polygon));
+                        return true;
+                    }), loops.end());
+                };
+                for (int d = 1; d <= loop_number; ++ d) {
+                    reduce_over_top(contours[d]);
+                    reduce_over_top(holes[d]);
+                }
+                if (! gaps.empty())
+                    gaps = diff_ex(gaps, one_wall_top_region);
+                if (! dropped_wall_bands.empty())
+                    one_wall_top_reclaimed = diff_ex(dropped_wall_bands, one_wall_top_region);
+            }
+
             // nest loops: holes first
             for (int d = 0; d <= loop_number; ++ d) {
                 PerimeterGeneratorLoops &holes_d = holes[d];
@@ -1634,7 +1843,10 @@ void PerimeterGenerator::process_classic()
                     and use zigzag).  */
                 //FIXME Vojtech: This grows by a rounded extrusion width, not by line spacing,
                 // therefore it may cover the area, but no the volume.
-                last = diff_ex(last, gap_fill.polygons_covered_by_width(10.f));
+                Polygons gap_fill_covered = gap_fill.polygons_covered_by_width(10.f);
+                last = diff_ex(last, gap_fill_covered);
+                if (! one_wall_top_reclaimed.empty())
+                    one_wall_top_reclaimed = diff_ex(one_wall_top_reclaimed, gap_fill_covered);
                 this->gap_fill->append(std::move(gap_fill.entities));
 
 			}
@@ -1679,9 +1891,15 @@ void PerimeterGenerator::process_classic()
         // append infill areas to fill_surfaces
         //if any top_fills, grow them by ext_perimeter_spacing/2 to have the real un-anchored fill
         ExPolygons top_infill_exp = intersection_ex(fill_clip, offset_ex(top_fills, double(ext_perimeter_spacing / 2)));
+        // ORCA: only_one_wall_top - route the top fill around the walls kept despite grazing the top.
+        if (!one_wall_top_kept_bands.empty())
+            top_infill_exp = diff_ex(top_infill_exp, one_wall_top_kept_bands);
         if (!top_fills.empty()) {
             infill_exp = union_ex(infill_exp, offset_ex(top_infill_exp, double(top_infill_peri_overlap)));
         }
+        // ORCA: only_one_wall_top - what the top fill does not cover of the dropped walls goes to infill.
+        if (!one_wall_top_reclaimed.empty())
+            infill_exp = union_ex(infill_exp, one_wall_top_reclaimed);
         this->fill_surfaces->append(infill_exp, stInternal);
 
         apply_extra_perimeters(infill_exp);
@@ -1700,6 +1918,8 @@ void PerimeterGenerator::process_classic()
                     double(-inset - infill_peri_overlap));
             if (!top_fills.empty())
                 polyWithoutOverlap = union_ex(polyWithoutOverlap, top_infill_exp);
+            if (!one_wall_top_reclaimed.empty())
+                polyWithoutOverlap = union_ex(polyWithoutOverlap, one_wall_top_reclaimed);
             this->fill_no_overlap->insert(this->fill_no_overlap->end(), polyWithoutOverlap.begin(), polyWithoutOverlap.end());
         }
 
@@ -2138,6 +2358,11 @@ void PerimeterGenerator::process_arachne()
     process_no_bridge(all_surfaces, perimeter_spacing, ext_perimeter_width);
     // BBS: don't simplify too much which influence arc fitting when export gcode if arc_fitting is enabled
     double surface_simplify_resolution = (print_config->enable_arc_fitting && !this->has_fuzzy_skin) ? 0.2 * m_scaled_resolution : m_scaled_resolution;
+    // ORCA: neither one-wall option has a surface to act on without the shell behind it, see
+    // has_top_shell_layers() / has_bottom_shell_layers(). Gated here so every use below - including the
+    // topmost and first layers - sees the same answer.
+    const bool only_one_wall_top         = this->config->only_one_wall_top && has_top_shell_layers(*this->config);
+    const bool only_one_wall_first_layer = this->config->only_one_wall_first_layer && has_bottom_shell_layers(*this->config);
     // we need to process each island separately because we might have different
     // extra perimeters for each one
     for (const Surface& surface : all_surfaces) {
@@ -2150,12 +2375,12 @@ void PerimeterGenerator::process_arachne()
 
         // Set the bottommost layer to be one wall
         const bool is_bottom_layer = (this->layer_id == object_config->raft_layers) ? true : false;
-        if (is_bottom_layer && this->config->only_one_wall_first_layer)
+        if (is_bottom_layer && only_one_wall_first_layer)
             loop_number = 0;
 
         // Orca: set the topmost layer to be one wall according to the config
         const bool is_topmost_layer = (this->upper_slices == nullptr) ? true : false;
-        if (is_topmost_layer && loop_number > 0 && config->only_one_wall_top)
+        if (is_topmost_layer && loop_number > 0 && only_one_wall_top)
             loop_number = 0;
         
         auto apply_precise_outer_wall = config->precise_outer_wall && config->wall_sequence == WallSequence::InnerOuter;
@@ -2175,10 +2400,10 @@ void PerimeterGenerator::process_arachne()
         //PS: One wall top surface for Arachne
         ExPolygons top_expolygons;
         // Calculate how many inner loops remain when TopSurfaces is selected.
-        const int inner_loop_number = (config->only_one_wall_top && upper_slices != nullptr) ? loop_number - 1 : -1;
+        const int inner_loop_number = (only_one_wall_top && upper_slices != nullptr) ? loop_number - 1 : -1;
 
         // Set one perimeter when TopSurfaces is selected.
-        if (config->only_one_wall_top && loop_number > 0)
+        if (only_one_wall_top && loop_number > 0)
             loop_number = 0;
 
         Arachne::WallToolPathsParams input_params_tmp = input_params;
@@ -2209,7 +2434,6 @@ void PerimeterGenerator::process_arachne()
                 upper_slices_clipped = ClipperUtils::clip_clipper_polygons_with_subject_bbox(*upper_slices, infill_contour_bbox);
 
             top_expolygons = diff_ex(infill_contour, upper_slices_clipped);
-            top_expolygons = fill_enclosed_top_feature_holes(top_expolygons, upper_slices_clipped, infill_contour);
 
             if (!top_expolygons.empty()) {
                 if (lower_slices != nullptr) {
@@ -2230,25 +2454,33 @@ void PerimeterGenerator::process_arachne()
                 // due to thin lines being generated
                 top_expolygons = offset2_ex(top_expolygons, -top_surface_min_width, top_surface_min_width + float(perimeter_width * 0.85));
 
-                // Get the not-top ExPolygons (including bridges) from current slices and expanded real top ExPolygons (without bridges).
-                const ExPolygons not_top_expolygons = diff_ex(infill_contour, top_expolygons);
-
-                // Get final top ExPolygons.
+                // Get final top ExPolygons (bridges were excluded above, so they stay walled).
                 top_expolygons = intersection_ex(top_expolygons, infill_contour);
 
-                const Polygons not_top_polygons = to_polygons(offset_ex(not_top_expolygons,wall_0_inset));
-                Arachne::WallToolPaths inner_wall_tool_paths(not_top_polygons, perimeter_spacing, perimeter_spacing, coord_t(inner_loop_number + 1), 0, layer_height, input_params_tmp);
+                // ORCA: onion the real region (inside the outer wall) so the remaining walls follow the actual
+                // geometry, then cut away the parts over the top surface. Re-onioning the non-top complement
+                // instead - the fallback when there is no top fill - walls the top/non-top interface and rings
+                // top-surface islands with inner walls that don't exist when the feature is disabled.
+                const bool     clip_walls_over_top = top_fill_replaces_inner_walls(*this->config);
+                const Polygons inner_region        = to_polygons(offset_ex(clip_walls_over_top ? infill_contour
+                                                                                               : diff_ex(infill_contour, top_expolygons),
+                                                                          wall_0_inset));
+                Arachne::WallToolPaths inner_wall_tool_paths(inner_region, perimeter_spacing, perimeter_spacing, coord_t(inner_loop_number + 1), 0, layer_height, input_params_tmp);
                 std::vector<Arachne::VariableWidthLines> inner_perimeters = inner_wall_tool_paths.getToolPaths();
 
-                // Recalculate indexes of inner perimeters before merging them.
-                if (!perimeters.empty()) {
-                    for (Arachne::VariableWidthLines &inner_perimeter : inner_perimeters) {
-                        if (inner_perimeter.empty())
-                            continue;
+                if (clip_walls_over_top) {
+                    Polygons kept_over_top;
+                    clip_inner_walls_over_top(inner_perimeters, top_expolygons, perimeter_width, kept_over_top);
+                    // Route the top fill around the walls kept despite grazing the top.
+                    if (! kept_over_top.empty())
+                        top_expolygons = diff_ex(top_expolygons, kept_over_top);
+                }
+
+                // Recalculate indexes of inner perimeters before merging them: they come after the single outer wall.
+                if (!perimeters.empty())
+                    for (Arachne::VariableWidthLines &inner_perimeter : inner_perimeters)
                         for (Arachne::ExtrusionLine &el : inner_perimeter)
                             ++el.inset_idx;
-                    }
-                }
 
                 perimeters.insert(perimeters.end(), inner_perimeters.begin(), inner_perimeters.end());
                 infill_contour = union_ex(top_expolygons, inner_wall_tool_paths.getInnerContour());

src/libslic3r/PrintConfig.cpp

@@ -332,6 +332,8 @@ CONFIG_OPTION_ENUM_DEFINE_STATIC_MAPS(PrintSequence)
 static t_config_enum_values s_keys_map_PrintOrder{
     { "default",     int(PrintOrder::Default) },
     { "as_obj_list", int(PrintOrder::AsObjectList)},
+    { "best_of",       int(PrintOrder::BestOfStrategies)},
+    { "snake", int(PrintOrder::Snake)},
 };
 CONFIG_OPTION_ENUM_DEFINE_STATIC_MAPS(PrintOrder)
 
@@ -2018,12 +2020,30 @@ void PrintConfigDef::init_fff_params()
 
     def = this->add("print_order", coEnum);
     def->label = L("Intra-layer order");
-    def->tooltip = L("Print order within a single layer.");
+    def->tooltip = L("Order in which object instances are visited within a single layer, which controls how much "
+                     "travel is spent moving between them.\n\n"
+                     "Default: nearest-neighbor chaining, refined with 2-opt and crossing removal. A good general "
+                     "choice.\n"
+                     "As object list: instances are printed in the same order as the object list, without any path "
+                     "optimization. Use it when you need a predictable, manually controlled order.\n"
+                     "Best of all (shortest path): every strategy is evaluated and the shortest one is used. The "
+                     "object instance order is decided once for the whole print, while the ordering of individual "
+                     "islands is decided per layer, so different layers may end up using different strategies. "
+                     "Slightly slower to slice.\n"
+                     "Snake: serpentine row-by-row traversal, refined with 2-opt. Well suited to regular grids of "
+                     "many small parts.\n\n"
+                     "With multiple filaments or tools in the same layer, minimizing tool changes takes priority: "
+                     "objects are grouped by filament first and this setting only orders the instances within each "
+                     "filament group, so the overall sequence may not look like the shortest path across the plate.");
     def->enum_keys_map = &ConfigOptionEnum<PrintOrder>::get_enum_values();
     def->enum_values.push_back("default");
     def->enum_values.push_back("as_obj_list");
+    def->enum_values.push_back("best_of");
+    def->enum_values.push_back("snake");
     def->enum_labels.push_back(L("Default"));
     def->enum_labels.push_back(L("As object list"));
+    def->enum_labels.push_back(L("Best of all (shortest path)"));
+    def->enum_labels.push_back(L("Snake"));
     def->mode = comAdvanced;
     def->set_default_value(new ConfigOptionEnum<PrintOrder>(PrintOrder::Default));
 
@@ -5648,6 +5668,7 @@ void PrintConfigDef::init_fff_params()
     // Orca:
     def = this->add("retract_after_wipe", coPercents);
     def->label = L("Retract amount after wipe");
+    // xgettext:no-c-format, no-boost-format
     def->tooltip = L("The length of fast retraction after wipe, relative to retraction length.\n"
                      "The value will be clamped by 100% minus the retract amount before the wipe value.");
     def->sidetext = "%";

src/libslic3r/PrintConfig.hpp

@@ -234,6 +234,8 @@ enum class PrintOrder
 {
     Default,
     AsObjectList,
+    BestOfStrategies,    // run all custom strategies, pick the shortest total path
+    Snake,               // snake-like row traversal (back-and-forth) + 2-opt
     Count,
 };
 

src/libslic3r/PrintObject.cpp

@@ -1364,7 +1364,6 @@ bool PrintObject::invalidate_state_by_config_options(
             || opt_key == "infill_combination_max_layer_height"
             || opt_key == "bottom_shell_thickness"
             || opt_key == "top_shell_thickness"
-            || opt_key == "top_surface_expansion"
             || opt_key == "top_surface_expansion_margin"
             || opt_key == "top_surface_expansion_direction"
             || opt_key == "minimum_sparse_infill_area"
@@ -1400,7 +1399,6 @@ bool PrintObject::invalidate_state_by_config_options(
             || opt_key == "infill_anchor"
             || opt_key == "infill_anchor_max"
             || opt_key == "top_surface_line_width"
-            || opt_key == "top_surface_density"
             || opt_key == "bottom_surface_density"
             || opt_key == "center_of_surface_pattern"
             || opt_key == "separated_infills" 
@@ -1434,6 +1432,24 @@ bool PrintObject::invalidate_state_by_config_options(
                 is_approx(new_density->value, 0.) || is_approx(new_density->value, 100.))
                 steps.emplace_back(posPerimeters);
             steps.emplace_back(posPrepareInfill);
+        } else if (opt_key == "top_surface_density") {
+            // ORCA: 0% means no top solid fill, which switches off both the top surface expansion and the wall
+            // removal over top surfaces. Only crossing zero matters; posPerimeters cascades to posPrepareInfill.
+            const auto *old_density = old_config.option<ConfigOptionPercent>(opt_key);
+            const auto *new_density = new_config.option<ConfigOptionPercent>(opt_key);
+            assert(old_density && new_density);
+            if (is_approx(old_density->value, 0.) || is_approx(new_density->value, 0.))
+                steps.emplace_back(posPerimeters);
+            steps.emplace_back(posInfill);
+        } else if (opt_key == "top_surface_expansion") {
+            // ORCA: without the expansion the top fill never reaches the space freed by only_one_wall_top, so the
+            // walls over top surfaces are kept. Only crossing zero matters; posPerimeters cascades to posPrepareInfill.
+            const auto *old_expansion = old_config.option<ConfigOptionFloat>(opt_key);
+            const auto *new_expansion = new_config.option<ConfigOptionFloat>(opt_key);
+            assert(old_expansion && new_expansion);
+            if (old_expansion->value <= 0. || new_expansion->value <= 0.)
+                steps.emplace_back(posPerimeters);
+            steps.emplace_back(posPrepareInfill);
         } else if (opt_key == "internal_solid_infill_line_width") {
             // This value is used for calculating perimeter - infill overlap, thus perimeters need to be recalculated.
             steps.emplace_back(posPerimeters);
@@ -1760,51 +1776,50 @@ void PrintObject::detect_surfaces_type()
                         }
                     }
 
-                    // ORCA: Expand the top surfaces outward by top_surface_expansion in every direction. This
-                    // enlarges the top solid infill and, in particular, grows it over the covered material left
-                    // by features rising from the middle of a top surface (filling holes and joining tops so the
-                    // features rest on it). The expansion stays inside the section it belongs to: each connected
-                    // solid island has its own outer wall, so the top is grown within each island separately and
-                    // clipped to it - growing one island's top across the gap into another island (which may have
-                    // no top surface, leaving a partially filled layer) is never allowed. The top infill sits
-                    // inside the perimeters, so the margin is measured from the walls: the island is inset by the
-                    // band the walls consume (outer wall + inner walls) plus the configured margin, making that
-                    // value the real clearance between the expanded top and the walls (avoiding a hull line). The
-                    // original top is unioned back in, so where it already sits within that band it is kept as-is.
-                    // Never claims a bottom surface.
-                    const double top_expansion = layerm->region().config().top_surface_expansion.value;
-                    if (top_expansion > 0. && ! top.empty()) {
-                        const double     d        = scale_(top_expansion);
-                        const auto       jt       = Clipper2Lib::JoinType::Miter;
-                        const ExPolygons T        = union_ex(to_expolygons(top));
-                        const int    wall_loops = layerm->region().config().wall_loops.value;
+                    // ORCA: Grow the top surfaces by top_surface_expansion, so the top solid infill also covers the
+                    // material left by features rising from the middle of a top surface (filling the holes and
+                    // joining the tops, so the features rest on solid infill). Each connected island is grown and
+                    // clipped separately: growing one island's top across a gap into another - which may have no top
+                    // surface at all, leaving a partially filled layer - is never allowed. The original top is
+                    // unioned back in and bottom surfaces are never claimed, so this can only add area.
+                    const PrintRegionConfig &region_config  = layerm->region().config();
+                    const double             top_expansion  = region_config.top_surface_expansion.value;
+                    // Nothing to expand without a top fill: a 0% top surface density leaves the top layer with
+                    // walls only, and zero top shell layers retypes it as internal in prepare_fill_surfaces().
+                    if (top_expansion > 0. && region_config.top_shell_layers.value > 0 &&
+                        region_config.top_surface_density.value > 0. && ! top.empty()) {
+                        const double     d = scale_(top_expansion);
+                        const ExPolygons T = union_ex(to_expolygons(top));
+                        // Walls are laid out on spacing, not width; and only_one_wall_top leaves a single wall over
+                        // a top surface, which is exactly the situation handled here.
+                        const int    wall_loops = region_config.only_one_wall_top.value ? std::min(region_config.wall_loops.value, 1)
+                                                                                        : region_config.wall_loops.value;
                         const double wall_band  = wall_loops <= 0 ? 0. :
                             double(layerm->flow(frExternalPerimeter).scaled_width()) +
-                            double(layerm->flow(frPerimeter).scaled_width()) * double(wall_loops - 1);
-                        const double margin     = scale_(layerm->region().config().top_surface_expansion_margin.value);
+                            double(layerm->flow(frPerimeter).scaled_spacing()) * double(wall_loops - 1);
+                        const double margin     = scale_(region_config.top_surface_expansion_margin.value);
                         // minimum real top to act on: ignore anything thinner than ~2 top-infill lines
                         const float  min_top    = float(layerm->flow(frTopSolidInfill).scaled_width());
-                        const auto   direction  = layerm->region().config().top_surface_expansion_direction.value;
+                        const auto   direction  = region_config.top_surface_expansion_direction.value;
 
                         ExPolygons grown;
                         for (const ExPolygon &island : union_ex(layerm_slices_surfaces)) {
                             // The top infill only exists inside the perimeters, so seed and measure from the infill
-                            // region (the island minus the wall band), not the raw slice. A section whose only
-                            // exposed top lies in the wall band - i.e. a layer where the top is just the walls
-                            // themselves - has no infill here and is skipped, instead of being flooded inward by
-                            // the expansion. Thin slivers inside the infill region are dropped by the opening too.
+                            // region (the island minus the wall band), not the raw slice: a section whose exposed top
+                            // is just the walls themselves is then skipped instead of being flooded inward. Clip the
+                            // layer's tops to the island first, to keep the boolean ops proportional to the island.
                             const ExPolygons infill_region = wall_band > 0. ? offset_ex(island, -float(wall_band)) : ExPolygons{ island };
-                            const ExPolygons island_top    = intersection_ex(T, infill_region);
+                            const ExPolygons island_top    = intersection_ex(
+                                ClipperUtils::clip_clipper_polygons_with_subject_bbox(T, get_extents(island).inflated(SCALED_EPSILON)),
+                                infill_region);
                             if (opening_ex(island_top, min_top).empty())
                                 continue; // no real top infill in this section - never expand into it
 
-                            // grow by d, then keep only the part allowed by the configured direction: inward fills
-                            // the holes/gaps left by features (clip the growth back to the top's own filled outline,
-                            // which leaves the outer edge fixed), outward grows the outer edge toward the walls (drop
-                            // the growth that fell into the original holes), and inward+outward keeps both.
-                            ExPolygons expanded = offset_ex_2(island_top, d, jt);
+                            // Grow, then keep only what the configured direction allows, using the top's own filled
+                            // outline (same outer edge, holes closed) to tell the two apart.
+                            ExPolygons expanded = offset_ex_2(island_top, d, Clipper2Lib::JoinType::Miter);
                             if (direction != TopSurfaceExpansionDirection::InwardAndOutward) {
-                                ExPolygons outline; // the top with its holes filled (same outer edge)
+                                ExPolygons outline;
                                 outline.reserve(island_top.size());
                                 for (const ExPolygon &ex : island_top)
                                     outline.emplace_back(ex.contour);

src/libslic3r/ShortestPath.cpp

@@ -10,6 +10,7 @@
 #include "KDTreeIndirect.hpp"
 #include "MutablePriorityQueue.hpp"
 #include "Print.hpp"
+#include "GCode/OrderingStrategies.hpp"
 
 #include <cmath>
 #include <cassert>
@@ -1103,7 +1104,7 @@ std::vector<size_t> chain_expolygons(const ExPolygons &input_exploy) {
 	return chain_points(points);
 }
 
-std::vector<size_t> chain_points(const Points &points, Point *start_near)
+std::vector<size_t> chain_points(const Points &points, const Point *start_near)
 {
 	auto segment_end_point = [&points](size_t idx, bool /* first_point */) -> const Point& { return points[idx]; };
 	std::vector<std::pair<size_t, bool>> ordered = chain_segments_greedy<Point, decltype(segment_end_point)>(segment_end_point, points.size(), start_near);
@@ -1111,9 +1112,26 @@ std::vector<size_t> chain_points(const Points &points, Point *start_near)
 	out.reserve(ordered.size());
 	for (auto &segment_and_reversal : ordered)
 		out.emplace_back(segment_and_reversal.first);
+
 	return out;
 }
 
+std::vector<size_t> chain_points_with_postprocessing(const Points &points, const Point *start_near)
+{
+	std::vector<size_t> path = chain_points(points, start_near);
+	// Alternate 2-opt and crossing removal until convergence.
+	// 2-opt can create new crossings, and crossing removal can create new
+	// opportunities for 2-opt improvement. Break early if neither improves.
+	for (int iter = 0; iter < 3; ++iter) {
+		bool improved = tsp_2opt_improve(path, points);
+		improved |= tsp_remove_crossings(path, points);
+		if (!improved) break;
+	}
+    if (start_near == nullptr)
+        tsp_rotate_minimize_closing(path, points);
+	return path;
+}
+
 #ifndef NDEBUG
 	// #define DEBUG_SVG_OUTPUT
 #endif /* NDEBUG */
@@ -2025,12 +2043,13 @@ std::vector<const PrintInstance*> chain_print_object_instances(const std::vector
 			instances.emplace_back(i, j);
 		}
 	}
-	auto segment_end_point = [&object_reference_points](size_t idx, bool /* first_point */) -> const Point& { return object_reference_points[idx]; };
-	std::vector<std::pair<size_t, bool>> ordered = chain_segments_greedy<Point, decltype(segment_end_point)>(segment_end_point, instances.size(), start_near);
+	// Order objects using nearest neighbor + post-processing (crossing removal + 2-opt).
+	std::vector<size_t> path = chain_points_with_postprocessing(object_reference_points, start_near);
+
 	std::vector<const PrintInstance*> out;
-	out.reserve(instances.size());
-	for (auto& segment_and_reversal : ordered) {
-		const std::pair<size_t, size_t>& inst = instances[segment_and_reversal.first];
+	out.reserve(path.size());
+	for (size_t idx : path) {
+		const std::pair<size_t, size_t>& inst = instances[idx];
 		out.emplace_back(&print_objects[inst.first]->instances()[inst.second]);
 	}
 	return out;

src/libslic3r/ShortestPath.hpp

@@ -15,7 +15,9 @@ namespace Slic3r {
 		using PolyNodes = std::vector<PolyNode*, PointsAllocator<PolyNode*>>;
 	}
 
-std::vector<size_t> 				 chain_points(const Points &points, Point *start_near = nullptr);
+std::vector<size_t> 				 chain_points(const Points &points, const Point *start_near = nullptr);
+// Variant with post-processing (crossing removal + 2-opt) for object ordering.
+std::vector<size_t> 				 chain_points_with_postprocessing(const Points &points, const Point *start_near = nullptr);
 std::vector<size_t> 				 chain_expolygons(const ExPolygons &input_exploy);
 
 std::vector<std::pair<size_t, bool>> chain_extrusion_entities(std::vector<ExtrusionEntity*> &entities, const Point *start_near = nullptr);

src/libslic3r/Support/SupportCommon.cpp

@@ -65,6 +65,15 @@ std::pair<SupportGeneratorLayersPtr, SupportGeneratorLayersPtr> generate_interfa
         const bool                 smooth_supports        = support_params.support_style != smsGrid;
         SupportGeneratorLayersPtr &interface_layers       = base_and_interface_layers.first;
         SupportGeneratorLayersPtr &base_interface_layers  = base_and_interface_layers.second;
+        // The user-facing interface layer counts include the contact layer. Internally,
+        // contact layers are generated separately, so only the remaining layers are
+        // projected into intermediate interface/base-interface layers here.
+        const size_t num_top_interface_layers    = support_params.has_top_contacts    ? support_params.num_top_interface_layers    - 1 : 0;
+        const size_t num_bottom_interface_layers = support_params.has_bottom_contacts ? support_params.num_bottom_interface_layers - 1 : 0;
+        const size_t num_top_base_interface_layers    = std::min(support_params.num_top_base_interface_layers,    num_top_interface_layers);
+        const size_t num_bottom_base_interface_layers = std::min(support_params.num_bottom_base_interface_layers, num_bottom_interface_layers);
+        const size_t num_top_interface_layers_only    = num_top_interface_layers    - num_top_base_interface_layers;
+        const size_t num_bottom_interface_layers_only = num_bottom_interface_layers - num_bottom_base_interface_layers;
 
         interface_layers.assign(intermediate_layers.size(), nullptr);
         if (support_params.has_base_interfaces())
@@ -124,6 +133,8 @@ std::pair<SupportGeneratorLayersPtr, SupportGeneratorLayersPtr> generate_interfa
         };
         tbb::parallel_for(tbb::blocked_range<int>(0, int(intermediate_layers.size())),
             [&bottom_contacts, &top_contacts, &top_interface_layers, &top_base_interface_layers, &intermediate_layers, &insert_layer, &support_params,
+             num_top_interface_layers, num_bottom_interface_layers, num_top_base_interface_layers, num_bottom_base_interface_layers,
+             num_top_interface_layers_only, num_bottom_interface_layers_only,
              snug_supports, &interface_layers, &base_interface_layers](const tbb::blocked_range<int>& range) {
                 // Gather the top / bottom contact layers intersecting with num_interface_layers resp. num_interface_layers_only intermediate layers above / below
                 // this intermediate layer.
@@ -142,16 +153,16 @@ std::pair<SupportGeneratorLayersPtr, SupportGeneratorLayersPtr> generate_interfa
                     Polygons polygons_top_contact_projected_base;
                     Polygons polygons_bottom_contact_projected_interface;
                     Polygons polygons_bottom_contact_projected_base;
-                    if (support_params.num_top_interface_layers > 0) {
+                    if (num_top_interface_layers > 0) {
                         // Top Z coordinate of a slab, over which we are collecting the top / bottom contact surfaces
-                        coordf_t top_z              = intermediate_layers[std::min(num_intermediate - 1, idx_intermediate_layer + int(support_params.num_top_interface_layers) - 1)]->print_z;
-                        coordf_t top_inteface_z     = std::numeric_limits<coordf_t>::max();
-                        if (support_params.num_top_base_interface_layers > 0)
+                        coordf_t top_z              = intermediate_layers[std::min(num_intermediate - 1, idx_intermediate_layer + int(num_top_interface_layers) - 1)]->print_z;
+                        coordf_t top_interface_z     = std::numeric_limits<coordf_t>::max();
+                        if (num_top_base_interface_layers > 0)
                             // Some top base interface layers will be generated.
-                            top_inteface_z = support_params.num_top_interface_layers_only() == 0 ?
+                            top_interface_z = num_top_interface_layers_only == 0 ?
                                 // Only base interface layers to generate.
                                 - std::numeric_limits<coordf_t>::max() :
-                                intermediate_layers[std::min(num_intermediate - 1, idx_intermediate_layer + int(support_params.num_top_interface_layers_only()) - 1)]->print_z;
+                                intermediate_layers[std::min(num_intermediate - 1, idx_intermediate_layer + int(num_top_interface_layers_only) - 1)]->print_z;
                         // Move idx_top_contact_first up until above the current print_z.
                         idx_top_contact_first = idx_higher_or_equal(top_contacts, idx_top_contact_first, [&intermediate_layer](const SupportGeneratorLayer *layer){ return layer->print_z >= intermediate_layer.print_z; }); //  - EPSILON
                         // Collect the top contact areas above this intermediate layer, below top_z.
@@ -160,22 +171,22 @@ std::pair<SupportGeneratorLayersPtr, SupportGeneratorLayersPtr> generate_interfa
                             //FIXME maybe this adds one interface layer in excess?
                             if (top_contact_layer.bottom_z - EPSILON > top_z)
                                 break;
-                            polygons_append(top_contact_layer.bottom_z - EPSILON > top_inteface_z ? polygons_top_contact_projected_base : polygons_top_contact_projected_interface,
+                            polygons_append(top_contact_layer.bottom_z - EPSILON > top_interface_z ? polygons_top_contact_projected_base : polygons_top_contact_projected_interface,
                                 // For snug supports, project the overhang polygons covering the whole overhang, so that they will merge without a gap with support polygons of the other layers.
                                 // For grid supports, merging of support regions will be performed by the projection into grid.
                                 snug_supports ? *top_contact_layer.overhang_polygons : top_contact_layer.polygons);
                         }
                     }
-                    if (support_params.num_bottom_interface_layers > 0) {
+                    if (num_bottom_interface_layers > 0) {
                         // Bottom Z coordinate of a slab, over which we are collecting the top / bottom contact surfaces
-                        coordf_t bottom_z           = intermediate_layers[std::max(0, idx_intermediate_layer - int(support_params.num_bottom_interface_layers) + 1)]->bottom_z;
+                        coordf_t bottom_z           = intermediate_layers[std::max(0, idx_intermediate_layer - int(num_bottom_interface_layers) + 1)]->bottom_z;
                         coordf_t bottom_interface_z = - std::numeric_limits<coordf_t>::max();
-                        if (support_params.num_bottom_base_interface_layers > 0)
+                        if (num_bottom_base_interface_layers > 0)
                             // Some bottom base interface layers will be generated.
-                            bottom_interface_z = support_params.num_bottom_interface_layers_only() == 0 ?
+                            bottom_interface_z = num_bottom_interface_layers_only == 0 ?
                                 // Only base interface layers to generate.
                                 std::numeric_limits<coordf_t>::max() :
-                                intermediate_layers[std::max(0, idx_intermediate_layer - int(support_params.num_bottom_interface_layers_only()))]->bottom_z;
+                                intermediate_layers[std::max(0, idx_intermediate_layer - int(num_bottom_interface_layers_only))]->bottom_z;
                         // Move idx_bottom_contact_first up until touching bottom_z.
                         idx_bottom_contact_first = idx_higher_or_equal(bottom_contacts, idx_bottom_contact_first, [bottom_z](const SupportGeneratorLayer *layer){ return layer->print_z >= bottom_z - EPSILON; });
                         // Collect the top contact areas above this intermediate layer, below top_z.
@@ -1563,13 +1574,17 @@ void generate_support_toolpaths(
         // Pointer to the 1st layer interface filler.
         auto filler_first_layer     = filler_first_layer_ptr ? filler_first_layer_ptr.get() : filler_interface.get();
         // Filler for the 1st layer interface, if different from filler_interface.
-        auto filler_raft_contact_ptr = std::unique_ptr<Fill>(range.begin() == n_raft_layers && config.support_interface_top_layers.value == 0 ?
+        const bool top_interfaces_enabled    = support_params.num_top_interface_layers > 0;
+        const bool bottom_interfaces_enabled = support_params.num_bottom_interface_layers > 0;
+        const coordf_t base_interface_density = top_interfaces_enabled || !bottom_interfaces_enabled ?
+            support_params.top_interface_density : support_params.bottom_interface_density;
+        auto filler_raft_contact_ptr = std::unique_ptr<Fill>(range.begin() == n_raft_layers && !top_interfaces_enabled ?
             Fill::new_from_type(support_params.raft_interface_fill_pattern) : nullptr);
         // Pointer to the 1st layer interface filler.
         auto filler_raft_contact     = filler_raft_contact_ptr ? filler_raft_contact_ptr.get() : filler_interface.get();
         // Filler for the base interface (to be used for soluble interface / non soluble base, to produce non soluble interface layer below soluble interface layer).
         auto filler_base_interface  = std::unique_ptr<Fill>(base_interface_layers.empty() ? nullptr :
-            Fill::new_from_type(support_params.top_interface_density > 0.95 || support_params.with_sheath ? ipRectilinear : ipSupportBase));
+            Fill::new_from_type(base_interface_density > 0.95 || support_params.with_sheath ? ipRectilinear : ipSupportBase));
         auto filler_support         = std::unique_ptr<Fill>(Fill::new_from_type(support_params.base_fill_pattern));
         filler_interface->set_bounding_box(bbox_object);
         if (filler_first_layer_ptr)
@@ -1583,10 +1598,7 @@ void generate_support_toolpaths(
         {
             SupportLayer &support_layer = *support_layers[support_layer_id];
             LayerCache   &layer_cache   = layer_caches[support_layer_id];
-            const float   support_interface_angle = (config.support_interface_pattern == smipRectilinearInterlaced) ?
-                support_params.raft_interface_angle(support_layer.interface_id()) :
-                ((support_params.support_style == smsGrid || config.support_interface_pattern == smipRectilinear) ?
-                support_params.interface_angle : support_params.raft_interface_angle(support_layer.interface_id()));
+            const float   support_interface_angle = support_params.support_interface_angle(support_layer.interface_id());
 
             // Find polygons with the same print_z.
             SupportGeneratorLayerExtruded &bottom_contact_layer = layer_cache.bottom_contact_layer;
@@ -1619,7 +1631,9 @@ void generate_support_toolpaths(
             bool raft_layer = slicing_params.interface_raft_layers && top_contact_layer.layer && is_approx(top_contact_layer.layer->print_z, slicing_params.raft_contact_top_z);
             // ORCA: Organic tree uses projected contacts to build the interface stack; avoid extra bottom-contact extrusion.
             const bool organic_tree = support_params.support_style == SupportMaterialStyle::smsTreeOrganic;
-            if (config.support_interface_top_layers == 0) {
+            const bool top_interfaces = support_params.num_top_interface_layers > 0;
+            const bool bottom_interfaces = support_params.num_bottom_interface_layers > 0;
+            if (!top_interfaces) {
                 // If no top interface layers were requested, we treat the contact layer exactly as a generic base layer.
                 // Don't merge the raft contact layer though.
                 if (support_params.can_merge_support_regions && ! raft_layer) {
@@ -1642,15 +1656,29 @@ void generate_support_toolpaths(
                 if (top_contact_layer.could_merge(interface_layer) && ! raft_layer)
                     top_contact_layer.merge(std::move(interface_layer));
             }
-            if ((config.support_interface_top_layers == 0 || config.support_interface_bottom_layers == 0) && support_params.can_merge_support_regions) {
+            if (!bottom_interfaces && support_params.can_merge_support_regions) {
                 if (base_layer.could_merge(bottom_contact_layer))
                     base_layer.merge(std::move(bottom_contact_layer));
                 else if (base_layer.empty() && ! bottom_contact_layer.empty() && ! bottom_contact_layer.layer->bridging)
                     base_layer = std::move(bottom_contact_layer);
             } else if (bottom_contact_layer.could_merge(top_contact_layer) && ! raft_layer) {
-                top_contact_layer.merge(std::move(bottom_contact_layer));
+                if (top_interfaces && bottom_interfaces) {
+                    top_contact_layer.merge(std::move(bottom_contact_layer));
+                } else if (bottom_interfaces) {
+                    top_contact_layer.set_polygons_to_extrude(
+                        diff(top_contact_layer.polygons_to_extrude(), bottom_contact_layer.polygons_to_extrude()));
+                } else {
+                    bottom_contact_layer.set_polygons_to_extrude(
+                        diff(bottom_contact_layer.polygons_to_extrude(), top_contact_layer.polygons_to_extrude()));
+                }
             } else if (bottom_contact_layer.could_merge(interface_layer) && ! organic_tree) {
-                bottom_contact_layer.merge(std::move(interface_layer));
+                const bool interface_layer_is_bottom = interface_layer.layer->layer_type == SupporLayerType::BottomInterface;
+                if (bottom_interfaces && interface_layer_is_bottom) {
+                    bottom_contact_layer.merge(std::move(interface_layer));
+                } else {
+                    bottom_contact_layer.set_polygons_to_extrude(
+                        diff(bottom_contact_layer.polygons_to_extrude(), interface_layer.polygons_to_extrude()));
+                }
             }
 
             // Orca: For organic trees the support-material regions are generated from
@@ -1730,12 +1758,12 @@ void generate_support_toolpaths(
                         interface_as_base ? ExtrusionRole::erSupportMaterial : ExtrusionRole::erSupportMaterialInterface, interface_flow);
                 }
             };
-            const bool top_interfaces = support_params.num_top_interface_layers > 0;
-            const bool bottom_interfaces = top_interfaces && support_params.num_bottom_interface_layers > 0;
             extrude_interface(top_contact_layer,    raft_layer ? InterfaceLayerType::RaftContact : top_interfaces ? InterfaceLayerType::TopContact : InterfaceLayerType::InterfaceAsBase);
             if (!organic_tree)
                 extrude_interface(bottom_contact_layer, bottom_interfaces ? InterfaceLayerType::BottomContact : InterfaceLayerType::InterfaceAsBase);
-            extrude_interface(interface_layer,      top_interfaces ? InterfaceLayerType::Interface : InterfaceLayerType::InterfaceAsBase);
+            const bool interface_layer_enabled = !interface_layer.empty() &&
+                (interface_layer.layer->layer_type == SupporLayerType::BottomInterface ? bottom_interfaces : top_interfaces);
+            extrude_interface(interface_layer,      interface_layer_enabled ? InterfaceLayerType::Interface : InterfaceLayerType::InterfaceAsBase);
             // Base interface layers under soluble interfaces
             if ( ! base_interface_layer.empty() && ! base_interface_layer.polygons_to_extrude().empty()) {
                 Fill *filler = filler_base_interface.get();
@@ -1745,7 +1773,7 @@ void generate_support_toolpaths(
                 Flow interface_flow = support_params.support_material_flow.with_height(float(base_interface_layer.layer->height));
                 filler->angle   = support_interface_angle;
                 filler->spacing = support_params.support_material_interface_flow.spacing();
-                    filler->link_max_length = coord_t(scale_(filler->spacing * link_max_length_factor / support_params.top_interface_density));
+                filler->link_max_length = coord_t(scale_(filler->spacing * link_max_length_factor / base_interface_density));
                 fill_expolygons_generate_paths(
                     // Destination
                     base_interface_layer.extrusions,
@@ -1753,7 +1781,7 @@ void generate_support_toolpaths(
                     // Regions to fill
                     union_safety_offset_ex(base_interface_layer.polygons_to_extrude()),
                     // Filler and its parameters
-                    filler, float(support_params.top_interface_density),
+                    filler, float(base_interface_density),
                     // Extrusion parameters
                     ExtrusionRole::erSupportMaterial, interface_flow);
             }

src/libslic3r/Support/SupportParameters.hpp

@@ -34,7 +34,7 @@ struct SupportParameters {
 
 	    {
 	        this->num_top_interface_layers    = std::max(0, object_config.support_interface_top_layers.value);
-	        this->num_bottom_interface_layers = number_of_support_interface_bottom_layers(object_config);
+	        this->num_bottom_interface_layers = std::max(0, number_of_support_interface_bottom_layers(object_config));
 	        this->has_top_contacts              = num_top_interface_layers    > 0;
 	        this->has_bottom_contacts           = num_bottom_interface_layers > 0;
             // BBS: if support interface and support base do not use the same filament, add a base layer to improve their adhesion
@@ -46,15 +46,15 @@ struct SupportParameters {
             if (non_soluble_base_top) { // ORCA: Try to support soluble dense interfaces with non-soluble dense interfaces.
                 this->num_top_base_interface_layers = size_t(std::min(int(num_top_interface_layers) / 2, 2));
             } else {
-                this->num_top_base_interface_layers =
-                    (different_support_interface_filament && this->zero_gap_interface_top) ? 1 : 0;
+                // Keep at least one configured layer on the interface filament.
+                this->num_top_base_interface_layers = different_support_interface_filament && num_top_interface_layers > 1 ? 1 : 0;
             }
 
             if (non_soluble_base_bottom) { // ORCA: Try to support soluble dense interfaces with non-soluble dense interfaces.
                 this->num_bottom_base_interface_layers = size_t(std::min(int(num_bottom_interface_layers) / 2, 2));
             } else {
-                this->num_bottom_base_interface_layers =
-                    (different_support_interface_filament && this->zero_gap_interface_bottom) ? 1 : 0;
+                // Keep at least one configured layer on the interface filament.
+                this->num_bottom_base_interface_layers = different_support_interface_filament && num_bottom_interface_layers > 1 ? 1 : 0;
             }
 	    }
         this->first_layer_flow = Slic3r::support_material_1st_layer_flow(&object, float(slicing_params.first_print_layer_height));
@@ -74,7 +74,7 @@ struct SupportParameters {
         for (auto layer : object.layers())
             this->support_layer_height_min = std::min(this->support_layer_height_min, std::max(0.01, layer->height));
         
-        if (object_config.support_interface_top_layers.value == 0) {
+        if (this->num_top_interface_layers == 0 && this->num_bottom_interface_layers == 0) {
             // No interface layers allowed, print everything with the base support pattern.
             this->support_material_interface_flow = this->support_material_flow;
         }
@@ -120,8 +120,8 @@ struct SupportParameters {
         this->raft_interface_density = std::min(1., this->raft_interface_flow.spacing() / raft_interface_spacing);
         this->support_spacing = object_config.support_base_pattern_spacing.value + this->support_material_flow.spacing();
         this->support_density = std::min(1., this->support_material_flow.spacing() / this->support_spacing);
-        if (object_config.support_interface_top_layers.value == 0) {
-            // No interface layers allowed, print everything with the base support pattern.
+        if (this->num_top_interface_layers == 0) {
+            // No top interface layers allowed; keep unused top interface parameters aligned with base support.
             this->top_interface_spacing = this->support_spacing;
             this->top_interface_density = this->support_density;
         }
@@ -133,16 +133,20 @@ struct SupportParameters {
             this->support_density > 0.95 || this->with_sheath ? ipRectilinear : ipSupportBase;
         this->interface_fill_pattern = (this->top_interface_density > 0.95 ? ipRectilinear : ipSupportBase);
         this->raft_interface_fill_pattern = this->raft_interface_density > 0.95 ? ipRectilinear : ipSupportBase;
+        const coordf_t contact_interface_density = this->num_top_interface_layers > 0 ?
+            this->top_interface_density : this->bottom_interface_density;
+        const bool zero_gap_contact_interface = this->num_top_interface_layers > 0 ?
+            this->zero_gap_interface_top : this->zero_gap_interface_bottom;
         if (object_config.support_interface_pattern == smipGrid)
             this->contact_fill_pattern = ipGrid;
         else if (object_config.support_interface_pattern == smipRectilinearInterlaced)
             this->contact_fill_pattern = ipRectilinear;
         else
             this->contact_fill_pattern =
-            (object_config.support_interface_pattern == smipAuto && this->zero_gap_interface_top) ||
+            (object_config.support_interface_pattern == smipAuto && zero_gap_contact_interface) ||
             object_config.support_interface_pattern == smipConcentric ?
             ipConcentric :
-            (this->top_interface_density > 0.95 ? ipRectilinear : ipSupportBase);
+            (contact_interface_density > 0.95 ? ipRectilinear : ipSupportBase);
 
         this->raft_angle_1st_layer  = 0.f;
         this->raft_angle_base       = 0.f;
@@ -188,6 +192,7 @@ struct SupportParameters {
                                                                                                           std::numeric_limits<double>::max();
 
         support_style = object_config.support_style;
+        support_interface_pattern = object_config.support_interface_pattern;
         if (support_style != smsDefault) {
             if ((support_style == smsSnug || support_style == smsGrid) && is_tree(object_config.support_type)) support_style = smsDefault;
             if ((support_style == smsTreeSlim || support_style == smsTreeStrong || support_style == smsTreeHybrid || support_style == smsTreeOrganic) &&
@@ -211,9 +216,9 @@ struct SupportParameters {
     bool                    has_top_contacts;
     // Is there at least a bottom contact layer extruded below support base?
     bool                    has_bottom_contacts;
-    // Number of top interface layers without counting the contact layer.
+    // User-configured number of top interface layers, including the contact layer.
     size_t                  num_top_interface_layers;
-    // Number of bottom interface layers without counting the contact layer.
+    // User-configured number of bottom interface layers, including the contact layer.
     size_t                  num_bottom_interface_layers;
     // Number of top base interface layers.
     size_t                  num_top_base_interface_layers;
@@ -235,7 +240,7 @@ struct SupportParameters {
 	Flow 					support_material_interface_flow;
 	// Flow at the bottom interfaces and contacts.
 	Flow 					support_material_bottom_interface_flow;
-	// Flow at raft inteface & contact layers.
+	// Flow at raft interface & contact layers.
 	Flow    				raft_interface_flow;
     coordf_t support_extrusion_width;
 	// Is merging of regions allowed? Could the interface & base support regions be printed with the same extruder?
@@ -262,6 +267,7 @@ struct SupportParameters {
     // Density of the base support layers.
     coordf_t 				support_density;
     SupportMaterialStyle    support_style = smsDefault;
+    SupportMaterialInterfacePattern support_interface_pattern = smipAuto;
 
     // Pattern of the sparse infill including sparse raft layers.
     InfillPattern           base_fill_pattern;
@@ -280,9 +286,33 @@ struct SupportParameters {
     float 					raft_angle_base;
     float 					raft_angle_interface;
 
-    // Produce a raft interface angle for a given SupportLayer::interface_id()
+    // Produce a +/-45deg alternating raft interface angle for a given SupportLayer::interface_id().
     float 					raft_interface_angle(size_t interface_id) const 
-    	{ return this->raft_angle_interface + ((interface_id & 1) ? float(- M_PI / 4.) : float(+ M_PI / 4.)); }
+    	{ return this->raft_angle_interface + ((interface_id & 1) ? float(- M_PI_4) : float(+ M_PI_4)); }
+
+    // Produce support interface angle for a given SupportLayer::interface_id().
+    // Angle will be shifted/rotated based on interface pattern.
+    float 					support_interface_angle(size_t interface_id) const 
+    	{ 
+            float angle;
+            
+            switch (this->support_interface_pattern) {
+                case SupportMaterialInterfacePattern::smipRectilinear:
+                    angle = support_style == SupportMaterialStyle::smsSnug ? this->interface_angle - float(M_PI_4) : this->interface_angle;
+                    break;
+                case SupportMaterialInterfacePattern::smipRectilinearInterlaced:
+                    angle = this->interface_angle + ((interface_id & 1) ? float(M_PI_4) : float(-M_PI_4));
+                    break;
+                case SupportMaterialInterfacePattern::smipGrid:
+                    angle = this->base_angle;
+                    break;
+                default:
+                    angle = this->interface_angle;
+                    break;
+            }
+
+            return angle;
+        }
 		
     bool independent_layer_height = false;
     const double thresh_big_overhang = Slic3r::sqr(scale_(10));

src/libslic3r/Support/TreeModelVolumes.cpp

@@ -469,7 +469,7 @@ 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, 
                     xy_distance, z_distance_bottom_layers, z_distance_top_layers, min_resolution = m_min_resolution, &data, processing_last_mesh, &throw_on_cancel]

src/libslic3r/Support/TreeSupport.cpp

@@ -1511,7 +1511,9 @@ void TreeSupport::generate_toolpaths()
                     // ORCA: reset interface Fill state per area group to keep angles deterministic.
                     filler_interface->fixed_angle = false;
                     filler_interface->layer_id = size_t(-1);
-                    filler_interface->angle = base_support_angle + M_PI_2; // default interface angle is perpendicular to support angle
+                    filler_Roof1stLayer->fixed_angle = false;
+                    filler_Roof1stLayer->layer_id = size_t(-1);
+                    filler_interface->angle = m_support_params.support_interface_angle(area_group.interface_id);
                     if (area_group.type != SupportLayer::BaseType) {
                         // interface
                         if (layer_id == 0) {
@@ -1537,8 +1539,10 @@ void TreeSupport::generate_toolpaths()
                         fill_params.density = interface_density;
                         // Note: spacing means the separation between two lines as if they are tightly extruded
                         filler_Roof1stLayer->spacing = interface_flow.spacing();
-                        filler_Roof1stLayer->angle = base_support_angle;
+                        filler_Roof1stLayer->angle = m_support_params.support_interface_angle(area_group.interface_id);
                         fill_params.dont_sort = true;
+                        filler_Roof1stLayer->fixed_angle = (m_object_config->support_interface_pattern == smipRectilinearInterlaced ||
+                                                            m_object_config->support_interface_pattern == smipRectilinear);
                         Flow interface_base_flow = interface_as_base ? support_flow : interface_flow;
                         ExtrusionRole interface_role = interface_as_base ? erSupportMaterial : erSupportMaterialInterface;
                         // generate a perimeter first to support interface better
@@ -1556,18 +1560,11 @@ void TreeSupport::generate_toolpaths()
                         fill_params.density = bottom_interface_density;
                         filler_interface->spacing = interface_flow.spacing();
 
-                        if (m_object_config->support_interface_pattern == smipGrid) {
-                            filler_interface->angle = base_support_angle;
-                            fill_params.dont_sort = true;
-                        }
-
-                        if (m_object_config->support_interface_pattern == smipRectilinearInterlaced) {
-                            // ORCA: explicit 0/90 alternation for rectilinear interlaced interfaces.
-                            filler_interface->fixed_angle = true;
-                            filler_interface->angle = base_support_angle + ((area_group.interface_id & 1) * M_PI_2);
-                            fill_params.dont_sort = true;
-                        }
+                        fill_params.dont_sort = (m_object_config->support_interface_pattern == smipGrid ||
+                                                m_object_config->support_interface_pattern == smipRectilinearInterlaced);   
 
+                        filler_interface->fixed_angle = (m_object_config->support_interface_pattern == smipRectilinearInterlaced ||
+                                                        m_object_config->support_interface_pattern == smipRectilinear);
 
                         Flow interface_base_flow = interface_as_base ? support_flow : interface_flow;
                         ExtrusionRole interface_role = interface_as_base ? erSupportMaterial : erSupportMaterialInterface;
@@ -1579,17 +1576,11 @@ void TreeSupport::generate_toolpaths()
                         fill_params.density       = interface_density;
                         filler_interface->spacing = interface_flow.spacing();
 
-                        if (m_object_config->support_interface_pattern == smipGrid) {
-                            filler_interface->angle = base_support_angle;
-                            fill_params.dont_sort = true;
-                        }
+                        fill_params.dont_sort = (m_object_config->support_interface_pattern == smipGrid ||
+                                                m_object_config->support_interface_pattern == smipRectilinearInterlaced);   
 
-                        if (m_object_config->support_interface_pattern == smipRectilinearInterlaced) {
-                            // ORCA: explicit 0/90 alternation for rectilinear interlaced interfaces.
-                            filler_interface->fixed_angle = true;
-                            filler_interface->angle = base_support_angle + ((area_group.interface_id & 1) * M_PI_2);
-                            fill_params.dont_sort = true;
-                        }
+                        filler_interface->fixed_angle = (m_object_config->support_interface_pattern == smipRectilinearInterlaced ||
+                                                        m_object_config->support_interface_pattern == smipRectilinear);
 
                         Flow interface_base_flow = interface_as_base ? support_flow : interface_flow;
                         ExtrusionRole interface_role = interface_as_base ? erSupportMaterial : erSupportMaterialInterface;
@@ -2014,6 +2005,9 @@ void TreeSupport::draw_circles()
     // generate areas
     const coordf_t layer_height = config.layer_height.value;
     const size_t top_interface_layers = m_support_params.num_top_interface_layers;
+    const int top_base_interface_layers = std::min<int>(
+        int(m_support_params.num_top_base_interface_layers),
+        top_interface_layers > 0 ? int(top_interface_layers) - 1 : 0);
     const size_t bottom_interface_layers = number_of_support_interface_bottom_layers(config);
     const double nozzle_diameter = m_object->print()->config().nozzle_diameter.get_at(0);
     const coordf_t line_width = config.get_abs_value("support_line_width", nozzle_diameter);
@@ -2054,12 +2048,14 @@ void TreeSupport::draw_circles()
 
                 ExPolygons& base_areas = ts_layer->base_areas;
                 ExPolygons& roof_areas = ts_layer->roof_areas;
+                ExPolygons roof_base_areas;
                 ExPolygons& roof_1st_layer = ts_layer->roof_1st_layer;
                 ExPolygons& floor_areas = ts_layer->floor_areas;
                 ExPolygons& roof_gap_areas = ts_layer->roof_gap_areas;
                 coordf_t         max_layers_above_base = 0;
                 coordf_t         max_layers_above_roof = 0;
                 coordf_t         max_layers_above_roof1 = 0;
+                size_t           first_base_roof_area = 0;
                 bool             floor_interface_as_base = false;
                 bool has_circle_node = false;
                 bool need_extra_wall = false;
@@ -2094,8 +2090,6 @@ void TreeSupport::draw_circles()
                         break;
 
                     const SupportNode& node = *p_node;
-                    // ORCA: Cap top interface height in mm based on per-node support layer height.
-                    const coordf_t top_interface_height = coordf_t(top_interface_layers) * node.height;
                     ExPolygons area;
                     // Generate directly from overhang polygon if one of the following is true:
                     // 1) node is a normal part of hybrid support
@@ -2159,18 +2153,16 @@ void TreeSupport::draw_circles()
 
                     if (obj_layer_nr>0 && node.distance_to_top < 0)
                         append(roof_gap_areas, area);
-                    // ORCA: Roof1stLayer must also fit inside the mm cap.
                     else if (obj_layer_nr > 0 && node.support_roof_layers_below == 1 &&
-                             (node.dist_mm_to_top - this->top_z_distance) < top_interface_height + EPSILON && node.is_sharp_tail==false)
+                             node.is_sharp_tail == false)
                     {
                         append(roof_1st_layer, area);
                         max_layers_above_roof1 = std::max(max_layers_above_roof1, node.dist_mm_to_top);
                     }
-                    // ORCA: Roof layers must also fit inside the mm cap.
                     else if (obj_layer_nr > 0 && node.support_roof_layers_below > 1 &&
-                             (node.dist_mm_to_top - this->top_z_distance) < top_interface_height + EPSILON && node.is_sharp_tail == false)
+                             node.is_sharp_tail == false)
                     {
-                        append(roof_areas, area);
+                        append(node.support_roof_layers_below <= top_base_interface_layers ? roof_base_areas : roof_areas, area);
                         max_layers_above_roof = std::max(max_layers_above_roof, node.dist_mm_to_top);
                     }
                     else
@@ -2184,9 +2176,17 @@ void TreeSupport::draw_circles()
                 //m_object->print()->set_status(65, (boost::format( _u8L("Support: generate polygons at layer %d")) % layer_nr).str());
 
                 // join roof segments
-                roof_areas     = diff_clipped(offset2_ex(roof_areas, line_width_scaled, -line_width_scaled), get_collision(false));
+                roof_areas     = diff_clipped(closing_ex(roof_areas, line_width_scaled), get_collision(false));
                 roof_areas     = intersection_ex(roof_areas, m_machine_border);
-                roof_1st_layer = diff_clipped(offset2_ex(roof_1st_layer, line_width_scaled, -line_width_scaled), get_collision(false));
+                roof_base_areas = diff_clipped(closing_ex(roof_base_areas, line_width_scaled), get_collision(false));
+                roof_base_areas = intersection_ex(roof_base_areas, m_machine_border);
+                if (!roof_base_areas.empty() && !roof_areas.empty())
+                    roof_base_areas = diff_ex(roof_base_areas,
+                        ClipperUtils::clip_clipper_polygons_with_subject_bbox(roof_areas, get_extents(roof_base_areas)));
+
+                first_base_roof_area = roof_areas.size();
+                append(roof_areas, std::move(roof_base_areas));
+                roof_1st_layer = diff_clipped(closing_ex(roof_1st_layer, line_width_scaled), get_collision(false));
 
                 // roof_1st_layer and roof_areas may intersect, so need to subtract roof_areas from roof_1st_layer
                 roof_1st_layer = diff_ex(roof_1st_layer, ClipperUtils::clip_clipper_polygons_with_subject_bbox(roof_areas,get_extents(roof_1st_layer)));
@@ -2366,9 +2366,11 @@ void TreeSupport::draw_circles()
                     area_groups.back().need_infill = overlaps({ expoly }, area_poly);
                     area_groups.back().need_extra_wall = need_extra_wall && !area_groups.back().need_infill;
                 }
-                for (auto& expoly : ts_layer->roof_areas) {
+                for (size_t roof_idx = 0; roof_idx < ts_layer->roof_areas.size(); ++roof_idx) {
+                    auto &expoly = ts_layer->roof_areas[roof_idx];
                     //if (area(expoly) < SQ(scale_(1))) continue;
                     area_groups.emplace_back(&expoly, SupportLayer::RoofType, max_layers_above_roof);
+                    area_groups.back().interface_as_base = roof_idx >= first_base_roof_area;
                 }
                 for (auto &expoly : ts_layer->floor_areas) {
                     //if (area(expoly) < SQ(scale_(1))) continue;
@@ -2378,6 +2380,7 @@ void TreeSupport::draw_circles()
                 for (auto &expoly : ts_layer->roof_1st_layer) {
                     //if (area(expoly) < SQ(scale_(1))) continue;
                     area_groups.emplace_back(&expoly, SupportLayer::Roof1stLayer, max_layers_above_roof1);
+                    area_groups.back().interface_as_base = top_base_interface_layers > 0;
                 }
 
                 for (auto &area_group : area_groups) {
@@ -2406,7 +2409,6 @@ void TreeSupport::draw_circles()
             }
         });
         // ORCA: normalize interface_id sequencing to follow printed interface layers only.
-        const int top_base_layers = int(m_support_params.num_top_base_interface_layers);
         const bool interlaced = m_object_config->support_interface_pattern == smipRectilinearInterlaced;
         int roof_interface_id = 0;
         int floor_interface_id = 0;
@@ -2425,7 +2427,6 @@ void TreeSupport::draw_circles()
                 if (area_group.type == SupportLayer::RoofType || area_group.type == SupportLayer::Roof1stLayer) {
                     if (interlaced)
                         area_group.interface_id = roof_interface_id;
-                    area_group.interface_as_base = top_base_layers > 0 && roof_interface_id < top_base_layers;
                     has_roof_interface = true;
                 } else if (area_group.type == SupportLayer::FloorType) {
                     if (interlaced)
@@ -2897,7 +2898,7 @@ void TreeSupport::drop_nodes()
                     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),
+                        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();
@@ -2949,7 +2950,7 @@ void TreeSupport::drop_nodes()
                     for(auto& overhang:overhangs_next) {
                         Point        next_pt     = overhang.contour.centroid();
                         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),
+                                                                          p_node->support_roof_layers_below - (p_node->distance_to_top >= 0 ? 1 : 0),
                                                                           to_buildplate, p_node, print_z_next, height_next);
                         next_node->max_move_dist = 0;
                         next_node->overhang = std::move(overhang);
@@ -3096,7 +3097,7 @@ void TreeSupport::drop_nodes()
                 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,
-                    node.support_roof_layers_below - (node.distance_to_top > 0 ? 1 : 0),
+                    node.support_roof_layers_below - (node.distance_to_top >= 0 ? 1 : 0),
                     to_buildplate, p_node, print_z_next, height_next);
                 // don't increase radius if next node will collide partially with the object (STUDIO-7883)
                 to_outside             = projection_onto(next_collision, next_node->position);
@@ -3376,21 +3377,6 @@ std::vector<LayerHeightData> TreeSupport::plan_layer_heights()
         }
     }
 
-    // ORCA: Recompute support_roof_layers_below from remaining interface height (independent heights).
-    const int top_layers = m_object->config().support_interface_top_layers.value;
-    if (m_support_params.independent_layer_height && top_layers > 0) {
-        const coordf_t interface_height_mm = coordf_t(top_layers) * m_slicing_params.layer_height;
-        for (int layer_nr = 0; layer_nr < contact_nodes.size(); layer_nr++) {
-            if (contact_nodes[layer_nr].empty()) continue;
-            for (SupportNode *node : contact_nodes[layer_nr]) {
-                if (node->height <= EPSILON) continue;
-                const coordf_t remaining_mm = interface_height_mm - (node->dist_mm_to_top - this->top_z_distance);
-                const int layers_fit = remaining_mm < -EPSILON ? 0 : int(std::floor((remaining_mm + EPSILON) / node->height));
-                node->support_roof_layers_below = std::min(layers_fit, top_layers);
-            }
-        }
-    }
-
     // log layer_heights
     for (size_t i = 0; i < layer_heights.size(); i++) {
         //if (layer_heights[i].height > EPSILON)
@@ -3498,7 +3484,7 @@ void TreeSupport::generate_contact_points()
                 if (force_add || !already_inserted.count(hash_pos)) {
                     already_inserted.emplace(hash_pos);
                     bool to_buildplate = true;
-                    size_t roof_layers = add_interface ? (support_roof_layers > 0 ? support_roof_layers - 1 : 0) : 0;  // subtract 1 because the contact node itself counts as one layer
+                    size_t roof_layers = add_interface ? support_roof_layers : 0;
                     // add a new node as a virtual node which acts as the invisible gap between support and object
                     // distance_to_top=-1: it's virtual
                     // print_z=object_layer->bottom_z: it directly contacts the bottom

src/libslic3r/Support/TreeSupport3D.cpp

@@ -706,7 +706,7 @@ static std::optional<std::pair<Point, size_t>> polyline_sample_next_point_at_dis
     filler->spacing  = flow.spacing();
     filler->angle = roof ?
         //fixme support_layer.interface_id() instead of layer_idx
-        (support_params.interface_angle + (layer_idx & 1) ? float(- M_PI / 4.) : float(+ M_PI / 4.)) :
+        (support_params.interface_angle + ((layer_idx & 1) ? float(- M_PI_4) : float(+ M_PI_4))) :
         support_params.base_angle;
 
     // ORCA: use top-specific interface density after separating top/bottom settings.

src/libslic3r/Support/TreeSupportCommon.hpp

@@ -62,7 +62,7 @@ struct TreeSupportMeshGroupSettings {
         this->support_line_width        = support_material_flow(&print_object, config.layer_height).scaled_width();
         this->support_roof_line_width   = support_material_interface_flow(&print_object, config.layer_height).scaled_width();
         const int bottom_interface_layers = number_of_support_interface_bottom_layers(config);
-        this->support_bottom_enable     = config.support_interface_top_layers.value > 0 && bottom_interface_layers > 0;
+        this->support_bottom_enable     = bottom_interface_layers > 0;
         this->support_bottom_height     = this->support_bottom_enable ?
             bottom_interface_layers * this->layer_height :
             0;
@@ -705,7 +705,7 @@ public:
     SupportGeneratorLayersPtr&  top_contacts_mutable() { return this->top_contacts; }
 
 public:
-    // Insert the contact layer and some of the inteface and base interface layers below.
+    // Insert the contact layer and some of the interface and base interface layers below.
     void add_roofs(std::vector<Polygons> &&new_roofs, const size_t insert_layer_idx)
     {
         if (! new_roofs.empty()) {

src/libslic3r/Technologies.hpp

@@ -51,4 +51,9 @@
 // Enable extension of tool position imgui dialog to show actual speed profile
 #define ENABLE_ACTUAL_SPEED_DEBUG 1
 
+// Disable layout inspector for public release
+#if BBL_RELEASE_TO_PUBLIC
+#define WXINSPECTOR_DISABLE
+#endif
+
 #endif // _prusaslicer_technologies_h_

src/libslic3r/calib.hpp

@@ -42,10 +42,22 @@ struct Calib_Params
     std::string shaper_type;
     std::vector<double> accelerations;
     std::vector<double> speeds;
+    // Resolved layer height for the VFA tower (0 = auto: nozzle_diameter / 2). Each speed block is a
+    // fixed number of layers tall, so this also determines the physical block height / tower height.
+    double vfa_layer_height = 0.0;
+    // Scale the calibration model to the nozzle diameter and set the layer height accordingly (temp tower / VFA).
+    // When false the 0.4 mm / 0.2 mm reference model is printed as-is.
+    bool nozzle_based_resize = true;
 
     CalibMode mode;
 };
 
+// Number of printed layers per speed block in the VFA tower. The base model has 5 mm blocks designed
+// for a 0.2 mm layer height (0.4 mm nozzle), i.e. 25 layers per block.
+static constexpr int vfa_layers_per_block = 25;
+static constexpr double vfa_base_block_height = 5.0;
+static constexpr double vfa_base_nozzle_diameter = 0.4;
+
 enum FlowRatioCalibrationType {
     COMPLETE_CALIBRATION = 0,
     FINE_CALIBRATION,