Read the Belt Tilt Only from the Belt G-code Header

Every printer's config block lists belt_slice_rotation_angle (default 45), so the processor marked all G-code as belt G-code: imported flat G-code got the belt view on a belt printer, and the belt-only Z handling in the processor ran for non-belt prints whose config block precedes the body. Take the angle only from outside the config block, where only the belt header writes it.

src/libslic3r/GCode/GCodeProcessor.cpp

@@ -3586,6 +3586,7 @@ void GCodeProcessor::reset()
     m_zero_layer_height = 0.0f;
     m_first_layer_height = 0.0f;
     m_processing_start_custom_gcode = false;
+    m_in_config_block = false;
     m_g1_line_id = 0;
     m_layer_id = 0;
     m_cp_color.reset();
@@ -4191,9 +4192,20 @@ void GCodeProcessor::process_tags(const std::string_view comment, bool producers
         return;
     }
 
+    if (boost::starts_with(comment, " CONFIG_BLOCK_START")) {
+        m_in_config_block = true;
+        return;
+    }
+    if (boost::starts_with(comment, " CONFIG_BLOCK_END")) {
+        m_in_config_block = false;
+        return;
+    }
+
     // Belt printer: derive the physical tilt magnitude from the slicing-rotation
-    // angle header comment (used to enable the preview's belt view).
+    // angle header comment (used to enable the preview's belt view). Only the belt
-    if (boost::starts_with(comment, " belt_slice_rotation_angle = ")) {
+    // header carries it outside the config block; the config block lists the key
+    // for every printer, belt or not.
+    if (!m_in_config_block && boost::starts_with(comment, " belt_slice_rotation_angle = ")) {
         try {
             m_result.belt_tilt_angle = std::abs(std::stof(std::string(comment.substr(29))));
         } catch (...) {}

src/libslic3r/GCode/GCodeProcessor.hpp

@@ -1194,6 +1194,7 @@ class Print;
         float m_first_layer_height; // mm
         float m_zero_layer_height; // mm
         bool m_processing_start_custom_gcode;
+        bool m_in_config_block;
         unsigned int m_g1_line_id;
         unsigned int m_layer_id;
         CpColor m_cp_color;

tests/fff_print/CMakeLists.txt

@@ -8,6 +8,7 @@ add_executable(${_TEST_NAME}_tests
 	test_extrusion_processor.cpp
 	test_fill.cpp
 	test_flow.cpp
+	test_gcode_processor.cpp
 	test_gcode_timing.cpp
 	test_gcodewriter.cpp
 	test_model.cpp

tests/fff_print/test_gcode_processor.cpp

@@ -0,0 +1,46 @@
+#include <catch2/catch_all.hpp>
+
+#include "libslic3r/libslic3r.h"
+#include "libslic3r/GCode/GCodeProcessor.hpp"
+#include "libslic3r/PrintConfig.hpp"
+
+#include "test_utils.hpp"
+
+#include <fstream>
+#include <string>
+
+using namespace Slic3r;
+using Catch::Matchers::WithinAbs;
+
+namespace {
+
+float processed_belt_tilt(const std::string &gcode)
+{
+    ScopedTemporaryFile temp(".gcode");
+    {
+        std::ofstream os(temp.string());
+        os << gcode;
+    }
+    GCodeProcessor proc;
+    proc.apply_config(FullPrintConfig{});
+    proc.process_file(temp.string());
+    return proc.get_result().belt_tilt_angle;
+}
+
+constexpr const char *body = "G1 X10 Y10 Z0.2 F3000\nG1 X20 Y10 E1 F1200\n";
+
+} // namespace
+
+TEST_CASE("The config block's belt angle does not mark G-code as belt G-code", "[GCodeProcessor][belt]")
+{
+    // Every printer's config block lists belt_slice_rotation_angle (default 45), belt or not.
+    const std::string gcode = std::string("; CONFIG_BLOCK_START\n; belt_printer = 0\n; belt_slice_rotation_angle = 45\n; CONFIG_BLOCK_END\n") + body;
+    CHECK_THAT(processed_belt_tilt(gcode), WithinAbs(0., 1e-6));
+}
+
+TEST_CASE("The belt header's angle marks G-code as belt G-code", "[GCodeProcessor][belt]")
+{
+    const std::string gcode = std::string("; belt_slice_rotation_angle = -45.0\n") + body +
+                              "; CONFIG_BLOCK_START\n; belt_printer = 1\n; belt_slice_rotation_angle = -45\n; CONFIG_BLOCK_END\n";
+    CHECK_THAT(processed_belt_tilt(gcode), WithinAbs(45., 1e-6));
+}