fix: multi-material slicing crash with line width 0 (#14455)

src/libslic3r/MultiMaterialSegmentation.cpp

@@ -1177,6 +1177,18 @@ static bool is_volume_sinking(const indexed_triangle_set &its, const Transform3d
 
 //#define MMU_SEGMENTATION_DEBUG_TOP_BOTTOM
 
+double resolve_outer_wall_line_width(const PrintRegionConfig &region_config, const PrintObjectConfig &object_config, const PrintConfig &print_config)
+{
+    // A filament id of 0 underflows, and get_at() then falls back to the first nozzle.
+    const double               nozzle_diameter = print_config.nozzle_diameter.get_at(region_config.outer_wall_filament_id - 1);
+    ConfigOptionFloatOrPercent width           = region_config.outer_wall_line_width;
+    if (width.value == 0)
+        width = object_config.line_width;
+    if (!width.percent && width.value <= 0.)
+        return Flow::auto_extrusion_width(frExternalPerimeter, float(nozzle_diameter));
+    return width.get_abs_value(nozzle_diameter);
+}
+
 // Returns segmentation of top and bottom layers based on painting in segmentation gizmos.
 static inline std::vector<std::vector<ExPolygons>> segmentation_top_and_bottom_layers(const PrintObject                                               &print_object,
                                                                                       const std::vector<ExPolygons>                                   &input_expolygons,
@@ -1347,8 +1359,7 @@ static inline std::vector<std::vector<ExPolygons>> segmentation_top_and_bottom_l
                 // As this region may split existing regions, we collect statistics over all regions for color_idx == 0.
                 color_idx == 0 || config.outer_wall_filament_id == int(color_idx)) {
                 //BBS: the extrusion line width is outer wall rather than inner wall
-                const double nozzle_diameter = print_object.print()->config().nozzle_diameter.get_at(0);
-                double outer_wall_line_width = config.get_abs_value("outer_wall_line_width", nozzle_diameter);
+                double outer_wall_line_width = resolve_outer_wall_line_width(config, print_object.config(), print_object.print()->config());
                 out.extrusion_width     = std::max<float>(out.extrusion_width, outer_wall_line_width);
                 out.top_shell_layers    = std::max<int>(out.top_shell_layers, config.top_shell_layers);
                 out.bottom_shell_layers = std::max<int>(out.bottom_shell_layers, config.bottom_shell_layers);

src/libslic3r/MultiMaterialSegmentation.hpp

@@ -9,6 +9,9 @@ namespace Slic3r {
 class ExPolygon;
 class ModelVolume;
 class PrintObject;
+class PrintConfig;
+class PrintObjectConfig;
+class PrintRegionConfig;
 class FacetsAnnotation;
 
 using ExPolygons = std::vector<ExPolygon>;
@@ -52,6 +55,9 @@ std::vector<std::vector<ExPolygons>> multi_material_segmentation_by_painting(con
 // Returns fuzzy skin segmentation based on painting in fuzzy skin segmentation gizmo
 std::vector<std::vector<ExPolygons>> fuzzy_skin_segmentation_by_painting(const PrintObject &print_object, const std::function<void()> &throw_on_cancel_callback);
 
+// Effective outer-wall line width for a region, resolved against its own nozzle with PrintRegion::flow's fallback.
+double resolve_outer_wall_line_width(const PrintRegionConfig &region_config, const PrintObjectConfig &object_config, const PrintConfig &print_config);
+
 } // namespace Slic3r
 
 namespace boost::polygon {

tests/libslic3r/CMakeLists.txt

@@ -19,6 +19,7 @@ add_executable(${_TEST_NAME}_tests
     test_preset_diff.cpp
     test_elephant_foot_compensation.cpp
     test_geometry.cpp
+    test_multimaterial_segmentation.cpp
     test_placeholder_parser.cpp
     test_polygon.cpp
     test_mutable_polygon.cpp

tests/libslic3r/test_multimaterial_segmentation.cpp

@@ -0,0 +1,57 @@
+#include <catch2/catch_all.hpp>
+
+// MultiMaterialSegmentation.hpp declares boost::polygon traits for ColoredLine, so its
+// geometry/boost dependencies must be included first.
+#include <boost/polygon/polygon.hpp>
+#include "libslic3r/Line.hpp"
+#include "libslic3r/Flow.hpp"
+#include "libslic3r/MultiMaterialSegmentation.hpp"
+#include "libslic3r/PrintConfig.hpp"
+
+using namespace Slic3r;
+
+TEST_CASE("Multi-material segmentation resolves the outer-wall line width", "[MultiMaterialSegmentation][Regression]")
+{
+    struct Case
+    {
+        std::string         description;
+        double              outer_value;
+        bool                outer_percent;
+        double              line_value;
+        bool                line_percent;
+        std::vector<double> nozzle_diameters;
+        int                 outer_wall_filament_id;
+        double              expected;
+    };
+
+    auto c = GENERATE(values<Case>({
+        {"absolute outer-wall width is used as-is",      0.6, false, 0.42, false, {0.4},      1, 0.6},
+        {"percent outer-wall width uses the nozzle",     120, true,  0.42, false, {0.5},      1, 0.6},
+        {"zero outer-wall width uses the line width",    0,   false, 0.5,  false, {0.4},      1, 0.5},
+        {"zero outer-wall width uses a percent line",    0,   false, 100,  true,  {0.5},      1, 0.5},
+        {"zero width falls back to auto",                0,   false, 0,    false, {0.4},      1, Flow::auto_extrusion_width(frExternalPerimeter, 0.4)},
+        {"the auto fallback scales with the nozzle",     0,   false, 0,    false, {0.6},      1, Flow::auto_extrusion_width(frExternalPerimeter, 0.6)},
+        {"a percent width uses the outer wall's nozzle", 120, true,  0.42, false, {0.4, 0.8}, 2, 0.96},
+        {"the auto width uses the outer wall's nozzle",  0,   false, 0,    false, {0.4, 0.8}, 2, Flow::auto_extrusion_width(frExternalPerimeter, 0.8)},
+        {"an absolute width ignores the nozzle",         0.6, false, 0.42, false, {0.4, 0.8}, 2, 0.6},
+        {"a zero percent width uses the line width",     0,   true,  0.5,  false, {0.4},      1, 0.5},
+        {"an unset filament id uses the first nozzle",   0,   false, 0,    false, {0.4, 0.8}, 0, Flow::auto_extrusion_width(frExternalPerimeter, 0.4)},
+        {"an out-of-range filament id uses nozzle 1",    0,   false, 0,    false, {0.4, 0.8}, 5, Flow::auto_extrusion_width(frExternalPerimeter, 0.4)},
+    }));
+
+    DYNAMIC_SECTION(c.description)
+    {
+        PrintConfig print_config;
+        print_config.nozzle_diameter.values = c.nozzle_diameters;
+
+        PrintObjectConfig object_config;
+        object_config.line_width = ConfigOptionFloatOrPercent(c.line_value, c.line_percent);
+
+        PrintRegionConfig region_config;
+        region_config.outer_wall_line_width        = ConfigOptionFloatOrPercent(c.outer_value, c.outer_percent);
+        region_config.outer_wall_filament_id.value = c.outer_wall_filament_id;
+
+        REQUIRE_THAT(resolve_outer_wall_line_width(region_config, object_config, print_config),
+                     Catch::Matchers::WithinAbs(c.expected, 1e-9));
+    }
+}