Gracefuly handle cases where the geometetry is not the same as generated perimeters

src/libslic3r/GCode/SeamGeometry.cpp

@@ -127,9 +127,16 @@ std::pair<Mapping, std::size_t> get_mapping(
     return {result, new_bucket_id};
 }
 
-Extrusion::Extrusion(BoundingBox bounding_box, const double width, const ExPolygon &island_boundary)
-    : bounding_box(std::move(bounding_box)), width(width), island_boundary(island_boundary) {
-
+Extrusion::Extrusion(
+    Polygon &&polygon,
+    BoundingBox bounding_box,
+    const double width,
+    const ExPolygon &island_boundary
+)
+    : polygon(polygon)
+    , bounding_box(std::move(bounding_box))
+    , width(width)
+    , island_boundary(island_boundary) {
     this->island_boundary_bounding_boxes.push_back(island_boundary.contour.bounding_box());
 
     std::transform(
@@ -149,9 +156,10 @@ Geometry::Extrusions get_external_perimeters(const Slic3r::Layer &layer, const L
             )};
             for (const ExtrusionEntity *entity : *collection) {
                 if (entity->role().is_external_perimeter()) {
-                    const BoundingBox bounding_box{entity->as_polyline().points};
+                    Polygon polygon{entity->as_polyline().points};
+                    const BoundingBox bounding_box{polygon.bounding_box()};
                     const double width{layer_region.flow(FlowRole::frExternalPerimeter).width()};
-                    result.emplace_back(bounding_box, width, island.boundary);
+                    result.emplace_back(std::move(polygon), bounding_box, width, island.boundary);
                 }
             }
         }
@@ -325,6 +333,12 @@ std::vector<double> get_vertex_angles(const std::vector<Vec2d> &points, const do
     return result;
 }
 
+double bounding_box_distance(const BoundingBox &a, const BoundingBox &b) {
+    const double bb_max_distance{unscaled(Point{a.max - b.max}).norm()};
+    const double bb_min_distance{unscaled(Point{a.min - b.min}).norm()};
+    return std::max(bb_max_distance, bb_min_distance);
+}
+
 std::pair<std::size_t, double> pick_closest_bounding_box(
     const BoundingBox &to, const BoundingBoxes &choose_from
 ) {
@@ -333,9 +347,7 @@ std::pair<std::size_t, double> pick_closest_bounding_box(
 
     for (std::size_t i{0}; i < choose_from.size(); ++i) {
         const BoundingBox &candidate{choose_from[i]};
-        const double bb_max_distance{unscaled(Point{candidate.max - to.max}).norm()};
-        const double bb_min_distance{unscaled(Point{candidate.min - to.min}).norm()};
-        const double distance{std::max(bb_max_distance, bb_min_distance)};
+        const double distance{bounding_box_distance(candidate, to)};
 
         if (distance < min_distance) {
             choosen_index = i;

src/libslic3r/GCode/SeamGeometry.hpp

@@ -18,13 +18,19 @@ namespace Slic3r::Seams::Geometry {
 
 struct Extrusion
 {
-    Extrusion(BoundingBox bounding_box, const double width, const ExPolygon &island_boundary);
+    Extrusion(
+        Polygon &&polygon,
+        BoundingBox bounding_box,
+        const double width,
+        const ExPolygon &island_boundary
+    );
 
     Extrusion(const Extrusion &) = delete;
     Extrusion(Extrusion &&) = default;
     Extrusion &operator=(const Extrusion &) = delete;
     Extrusion &operator=(Extrusion &&) = delete;
 
+    Polygon polygon;
     BoundingBox bounding_box;
     double width;
     const ExPolygon &island_boundary;
@@ -151,6 +157,8 @@ std::vector<double> get_overhangs(
 // Measured from outside, convex is positive
 std::vector<double> get_vertex_angles(const std::vector<Vec2d> &points, const double min_arm_length);
 
+double bounding_box_distance(const BoundingBox &a, const BoundingBox &b);
+
 std::pair<std::size_t, double> pick_closest_bounding_box(
     const BoundingBox &to, const BoundingBoxes &choose_from
 );

src/libslic3r/GCode/SeamShells.cpp

@@ -5,7 +5,7 @@
 
 namespace Slic3r::Seams::Shells::Impl {
 
-BoundedPolygons project_to_geometry(const Geometry::Extrusions &external_perimeters) {
+BoundedPolygons project_to_geometry(const Geometry::Extrusions &external_perimeters, const double max_bb_distance) {
     BoundedPolygons result;
     result.reserve(external_perimeters.size());
 
@@ -13,12 +13,26 @@ BoundedPolygons project_to_geometry(const Geometry::Extrusions &external_perimet
 
     transform(
         external_perimeters.begin(), external_perimeters.end(), back_inserter(result),
-        [](const Geometry::Extrusion &external_perimeter) {
+        [&](const Geometry::Extrusion &external_perimeter) {
             const auto [choosen_index, _]{Geometry::pick_closest_bounding_box(
                 external_perimeter.bounding_box,
                 external_perimeter.island_boundary_bounding_boxes
             )};
 
+            const double distance{Geometry::bounding_box_distance(
+                external_perimeter.island_boundary_bounding_boxes[choosen_index],
+                external_perimeter.bounding_box
+            )};
+
+            if (distance > max_bb_distance) {
+                Polygons expanded_extrusion{expand(external_perimeter.polygon, external_perimeter.width / 2.0)};
+                if (!expanded_extrusion.empty()) {
+                    return BoundedPolygon{
+                        expanded_extrusion.front(), expanded_extrusion.front().bounding_box(), external_perimeter.polygon.is_clockwise()
+                    };
+                }
+            }
+
             const bool is_hole{choosen_index != 0};
             const Polygon &adjacent_boundary{
                 !is_hole ? external_perimeter.island_boundary.contour :
@@ -29,11 +43,11 @@ BoundedPolygons project_to_geometry(const Geometry::Extrusions &external_perimet
     return result;
 }
 
-std::vector<BoundedPolygons> project_to_geometry(const std::vector<Geometry::Extrusions> &extrusions) {
+std::vector<BoundedPolygons> project_to_geometry(const std::vector<Geometry::Extrusions> &extrusions, const double max_bb_distance) {
     std::vector<BoundedPolygons> result(extrusions.size());
 
     for (std::size_t layer_index{0}; layer_index < extrusions.size(); ++layer_index) {
-        result[layer_index] = project_to_geometry(extrusions[layer_index]);
+        result[layer_index] = project_to_geometry(extrusions[layer_index], max_bb_distance);
     }
 
     return result;
@@ -61,7 +75,7 @@ namespace Slic3r::Seams::Shells {
 Shells<Polygon> create_shells(
     const std::vector<Geometry::Extrusions> &extrusions, const double max_distance
 ) {
-    std::vector<Impl::BoundedPolygons> projected{Impl::project_to_geometry(extrusions)};
+    std::vector<Impl::BoundedPolygons> projected{Impl::project_to_geometry(extrusions, max_distance)};
 
     std::vector<std::size_t> layer_sizes;
     layer_sizes.reserve(projected.size());

src/libslic3r/GCode/SeamShells.hpp

@@ -25,21 +25,7 @@ struct BoundedPolygon {
 
 using BoundedPolygons = std::vector<BoundedPolygon>;
 
-/**
- * Project extrusion path to the original mesh.
- *
- * Takes the extrusion path and finds the closest polygon to it in
- * the extruison island boundary.
- *
- * Then it expands the extrusion path so it roughly tracks the island boundary
- * and check that all points in expanded extrusion path are within a reasonable
- * distance (extrusion width) from the closes polygon.
- *
- * If the expanded extrusion path matches the boundary it returns the
- * closeset polygon from the island boundary. Otherwise it returns
- * the expanded extrusion.
- */
-BoundedPolygons project_to_geometry(const Geometry::Extrusions &extrusions);
+BoundedPolygons project_to_geometry(const Geometry::Extrusions &extrusions, const double max_bb_distance);
 }
 
 namespace Slic3r::Seams::Shells {

tests/fff_print/test_seam_shells.cpp

@@ -23,7 +23,7 @@ struct ProjectionFixture
     double extrusion_width{0.2};
 
     ProjectionFixture() {
-        extrusions.emplace_back(extrusion_path.bounding_box(), extrusion_width, island_boundary);
+        extrusions.emplace_back(Polygon{extrusion_path}, extrusion_path.bounding_box(), extrusion_width, island_boundary);
     }
 };
 
@@ -33,13 +33,31 @@ TEST_CASE_METHOD(ProjectionFixture, "Project to geometry matches", "[Seams][Seam
     boundary_polygon.scale(1.0 + extrusion_width / 2.0 + 0.1);
     island_boundary.contour = boundary_polygon;
 
-    Shells::Impl::BoundedPolygons result{Shells::Impl::project_to_geometry(extrusions)};
+    Shells::Impl::BoundedPolygons result{Shells::Impl::project_to_geometry(extrusions, 5.0)};
     REQUIRE(result.size() == 1);
     REQUIRE(result[0].polygon.size() == 4);
     // Boundary polygon is picked.
     CHECK(result[0].polygon[0].x() == Approx(scaled(-(1.0 + extrusion_width / 2.0 + 0.1))));
 }
 
+TEST_CASE_METHOD(ProjectionFixture, "Project to geometry does not match", "[Seams][SeamShells]") {
+    Polygon boundary_polygon{extrusion_path};
+
+    // Island boundary is far from the extrusion.
+    boundary_polygon.scale(5.0);
+
+    island_boundary.contour = boundary_polygon;
+
+    Shells::Impl::BoundedPolygons result{Shells::Impl::project_to_geometry(extrusions, 1.0)};
+    REQUIRE(result.size() == 1);
+    REQUIRE(result[0].polygon.size() == 4);
+
+    const Polygon expanded{expand(extrusions.front().polygon, extrusion_width / 2.0).front()};
+
+    // The extrusion is expanded and returned.
+    CHECK(result[0].polygon == expanded);
+}
+
 void serialize_shells(
     std::ostream &out, const Shells::Shells<Polygon> &shells, const double layer_height
 ) {
@@ -69,5 +87,5 @@ TEST_CASE_METHOD(Test::SeamsFixture, "Create shells", "[Seams][SeamShells][Integ
         serialize_shells(csv, shell_polygons, print->full_print_config().opt_float("layer_height"));
     }
 
-    CHECK(shell_polygons.size() == 39);
+    CHECK(shell_polygons.size() == 36);
 }