Reworked "only_retract_when_crossing_perimeters" feature, which

was terribly slow:
Introduced RetractWhenCrossingPerimeters.cpp,hpp
AABBTreeIndirect traverse template was extended to support early exit.

src/libslic3r/AABBTreeIndirect.hpp

@@ -920,29 +920,35 @@ template<class G> auto within(const G &g) { return Within<G>{g}; }
 
 namespace detail {
 
+// Returns true in case traversal should continue,
+// returns false if traversal should stop (for example if the first hit was found).
 template<int Dims, typename T, typename Pred, typename Fn>
-void traverse_recurse(const Tree<Dims, T> &tree,
+bool traverse_recurse(const Tree<Dims, T> &tree,
                       size_t               idx,
                       Pred &&              pred,
                       Fn &&                callback)
 {
     assert(tree.node(idx).is_valid());
 
-    if (!pred(tree.node(idx))) return;
+    if (!pred(tree.node(idx))) 
+    	// Continue traversal.
+    	return true;
 
     if (tree.node(idx).is_leaf()) {
-        callback(tree.node(idx));
+    	// Callback returns true to continue traversal, false to stop traversal.
+        return callback(tree.node(idx));
     } else {
 
         // call this with left and right node idx:
-        auto trv = [&](size_t idx) {
-            traverse_recurse(tree, idx, std::forward<Pred>(pred),
-                             std::forward<Fn>(callback));
+        auto trv = [&](size_t idx) -> bool {
+            return traverse_recurse(tree, idx, std::forward<Pred>(pred),
+                                    std::forward<Fn>(callback));
         };
 
         // Left / right child node index.
-        trv(Tree<Dims, T>::left_child_idx(idx));
-        trv(Tree<Dims, T>::right_child_idx(idx));
+        // Returns true if both children allow the traversal to continue.
+        return trv(Tree<Dims, T>::left_child_idx(idx)) &&
+        	   trv(Tree<Dims, T>::right_child_idx(idx));
     }
 }
 
@@ -952,6 +958,7 @@ void traverse_recurse(const Tree<Dims, T> &tree,
 // traverse(tree, intersecting(QueryBox), [](size_t face_idx) {
 //      /* ... */
 // });
+// Callback shall return true to continue traversal, false if it wants to stop traversal, for example if it found the answer.
 template<int Dims, typename T, typename Predicate, typename Fn>
 void traverse(const Tree<Dims, T> &tree, Predicate &&pred, Fn &&callback)
 {

src/libslic3r/CMakeLists.txt

@@ -130,6 +130,8 @@ set(SLIC3R_SOURCES
     GCode/PressureEqualizer.hpp
     GCode/PrintExtents.cpp
     GCode/PrintExtents.hpp
+    GCode/RetractWhenCrossingPerimeters.cpp
+    GCode/RetractWhenCrossingPerimeters.hpp
     GCode/SpiralVase.cpp
     GCode/SpiralVase.hpp
     GCode/SeamPlacer.cpp

src/libslic3r/ClipperUtils.cpp

@@ -140,6 +140,21 @@ namespace ClipperUtils {
         out.reserve(src.size());
         for (const Polygon &p : src)
             out.emplace_back(clip_clipper_polygon_with_subject_bbox(p, bbox));
+        out.erase(
+            std::remove_if(out.begin(), out.end(), [](const Polygon &polygon) { return polygon.empty(); }),
+            out.end());
+        return out;
+    }
+    [[nodiscard]] Polygons clip_clipper_polygons_with_subject_bbox(const ExPolygon &src, const BoundingBox &bbox)
+    {
+        Polygons out;
+        out.reserve(src.num_contours());
+        out.emplace_back(clip_clipper_polygon_with_subject_bbox(src.contour, bbox));
+        for (const Polygon &p : src.holes)
+            out.emplace_back(clip_clipper_polygon_with_subject_bbox(p, bbox));
+        out.erase(
+            std::remove_if(out.begin(), out.end(), [](const Polygon &polygon) { return polygon.empty(); }),
+            out.end());
         return out;
     }
 }
@@ -794,6 +809,8 @@ Polylines _clipper_pl_closed(ClipperLib::ClipType clipType, PathProvider1 &&subj
     return retval;
 }
 
+Slic3r::Polylines diff_pl(const Slic3r::Polyline &subject, const Slic3r::Polygons &clip)
+    { return _clipper_pl_open(ClipperLib::ctDifference, ClipperUtils::SinglePathProvider(subject.points), ClipperUtils::PolygonsProvider(clip)); }
 Slic3r::Polylines diff_pl(const Slic3r::Polylines &subject, const Slic3r::Polygons &clip)
     { return _clipper_pl_open(ClipperLib::ctDifference, ClipperUtils::PolylinesProvider(subject), ClipperUtils::PolygonsProvider(clip)); }
 Slic3r::Polylines diff_pl(const Slic3r::Polyline &subject, const Slic3r::ExPolygon &clip)

src/libslic3r/ClipperUtils.hpp

@@ -323,6 +323,7 @@ namespace ClipperUtils {
     void                    clip_clipper_polygon_with_subject_bbox(const Polygon &src, const BoundingBox &bbox, Polygon &out);
     [[nodiscard]] Polygon   clip_clipper_polygon_with_subject_bbox(const Polygon &src, const BoundingBox &bbox);
     [[nodiscard]] Polygons  clip_clipper_polygons_with_subject_bbox(const Polygons &src, const BoundingBox &bbox);
+    [[nodiscard]] Polygons  clip_clipper_polygons_with_subject_bbox(const ExPolygon &src, const BoundingBox &bbox);
 }
 
 // offset Polygons
@@ -427,6 +428,7 @@ Slic3r::ExPolygons diff_ex(const Slic3r::Surfaces &subject, const Slic3r::ExPoly
 Slic3r::ExPolygons diff_ex(const Slic3r::ExPolygons &subject, const Slic3r::Surfaces &clip, ApplySafetyOffset do_safety_offset = ApplySafetyOffset::No);
 Slic3r::ExPolygons diff_ex(const Slic3r::Surfaces &subject, const Slic3r::Surfaces &clip, ApplySafetyOffset do_safety_offset = ApplySafetyOffset::No);
 Slic3r::ExPolygons diff_ex(const Slic3r::SurfacesPtr &subject, const Slic3r::Polygons &clip, ApplySafetyOffset do_safety_offset = ApplySafetyOffset::No);
+Slic3r::Polylines  diff_pl(const Slic3r::Polyline &subject, const Slic3r::Polygons &clip);
 Slic3r::Polylines  diff_pl(const Slic3r::Polylines &subject, const Slic3r::Polygons &clip);
 Slic3r::Polylines  diff_pl(const Slic3r::Polyline &subject, const Slic3r::ExPolygon &clip);
 Slic3r::Polylines  diff_pl(const Slic3r::Polyline &subject, const Slic3r::ExPolygons &clip);

src/libslic3r/GCode.cpp

@@ -3090,7 +3090,7 @@ bool GCode::needs_retraction(const Polyline &travel, ExtrusionRole role)
         }
 
     if (m_config.only_retract_when_crossing_perimeters && m_layer != nullptr &&
-        m_config.fill_density.value > 0 && m_layer->any_internal_region_slice_contains(travel))
+        m_config.fill_density.value > 0 && m_retract_when_crossing_perimeters.travel_inside_internal_regions(*m_layer, travel))
         // Skip retraction if travel is contained in an internal slice *and*
         // internal infill is enabled (so that stringing is entirely not visible).
         //FIXME any_internal_region_slice_contains() is potentionally very slow, it shall test for the bounding boxes first.

src/libslic3r/GCode.hpp

@@ -12,6 +12,7 @@
 #include "GCode/AvoidCrossingPerimeters.hpp"
 #include "GCode/CoolingBuffer.hpp"
 #include "GCode/FindReplace.hpp"
+#include "GCode/RetractWhenCrossingPerimeters.hpp"
 #include "GCode/SpiralVase.hpp"
 #include "GCode/ToolOrdering.hpp"
 #include "GCode/WipeTower.hpp"
@@ -349,6 +350,7 @@ private:
     Wipe                                m_wipe;
     AvoidCrossingPerimeters             m_avoid_crossing_perimeters;
     JPSPathFinder                       m_avoid_curled_filaments;
+    RetractWhenCrossingPerimeters       m_retract_when_crossing_perimeters;
     bool                                m_enable_loop_clipping;
     // If enabled, the G-code generator will put following comments at the ends
     // of the G-code lines: _EXTRUDE_SET_SPEED, _WIPE, _BRIDGE_FAN_START, _BRIDGE_FAN_END

src/libslic3r/GCode/RetractWhenCrossingPerimeters.cpp

@@ -0,0 +1,67 @@
+#include "../ClipperUtils.hpp"
+#include "../Layer.hpp"
+#include "../Polyline.hpp"
+
+#include "RetractWhenCrossingPerimeters.hpp"
+
+namespace Slic3r {
+
+bool RetractWhenCrossingPerimeters::travel_inside_internal_regions(const Layer &layer, const Polyline &travel)
+{
+    if (m_layer != &layer) {
+        // Update cache.
+        m_layer = &layer;
+        m_internal_islands.clear();
+        m_aabbtree_internal_islands.clear();
+        // Collect expolygons of internal slices.
+        for (const LayerRegion *layerm : layer.regions())
+            for (const Surface &surface : layerm->slices().surfaces)
+                if (surface.is_internal())
+                    m_internal_islands.emplace_back(&surface.expolygon);
+        // Calculate bounding boxes of internal slices.
+        class BBoxWrapper {
+        public:
+            BBoxWrapper(const size_t idx, const BoundingBox &bbox) : 
+                m_idx(idx),
+                // Inflate the bounding box a bit to account for numerical issues.
+                m_bbox(bbox.min - Point(SCALED_EPSILON, SCALED_EPSILON), bbox.max + Point(SCALED_EPSILON, SCALED_EPSILON)) {}
+            size_t                       idx() const { return m_idx; }
+            const AABBTree::BoundingBox& bbox() const { return m_bbox; }
+            Point                        centroid() const { return ((m_bbox.min().cast<int64_t>() + m_bbox.max().cast<int64_t>()) / 2).cast<int32_t>(); }
+        private:
+            size_t                m_idx;
+            AABBTree::BoundingBox m_bbox;
+        };
+        std::vector<BBoxWrapper> bboxes;
+        bboxes.reserve(m_internal_islands.size());
+        for (size_t i = 0; i < m_internal_islands.size(); ++ i)
+            bboxes.emplace_back(i, get_extents(*m_internal_islands[i]));
+        // Build AABB tree over bounding boxes of internal slices.
+        m_aabbtree_internal_islands.build_modify_input(bboxes);
+    }
+
+    BoundingBox           bbox_travel = get_extents(travel);
+    AABBTree::BoundingBox bbox_travel_eigen{ bbox_travel.min, bbox_travel.max };
+    int result = -1;
+    bbox_travel.offset(SCALED_EPSILON);
+    AABBTreeIndirect::traverse(m_aabbtree_internal_islands, 
+        [&bbox_travel_eigen](const AABBTree::Node &node) {
+            return bbox_travel_eigen.intersects(node.bbox);
+        },
+        [&travel, &bbox_travel, &result, &islands = m_internal_islands](const AABBTree::Node &node) {
+            assert(node.is_leaf());
+            assert(node.is_valid());
+            Polygons clipped = ClipperUtils::clip_clipper_polygons_with_subject_bbox(*islands[node.idx], bbox_travel);
+            if (diff_pl(travel, clipped).empty()) {
+                // Travel path is completely inside an "internal" island. Don't retract.
+                result = int(node.idx);
+                // Stop traversal.
+                return false;
+            }
+            // Continue traversal.
+            return true;
+        });
+    return result != -1;
+}
+
+} // namespace Slic3r

src/libslic3r/GCode/RetractWhenCrossingPerimeters.hpp

@@ -0,0 +1,32 @@
+#ifndef slic3r_RetractWhenCrossingPerimeters_hpp_
+#define slic3r_RetractWhenCrossingPerimeters_hpp_
+
+#include <vector>
+
+#include "../AABBTreeIndirect.hpp"
+
+namespace Slic3r {
+
+// Forward declarations.
+class ExPolygon;
+class Layer;
+class Polyline;
+
+class RetractWhenCrossingPerimeters
+{
+public:
+    bool    travel_inside_internal_regions(const Layer &layer, const Polyline &travel);
+
+private:
+    // Last object layer visited, for which a cache of internal islands was created.
+    const Layer                        *m_layer;
+    // Internal islands only, referencing data owned by m_layer->regions()->surfaces().
+    std::vector<const ExPolygon*>       m_internal_islands;
+    // Search structure over internal islands.
+    using AABBTree = AABBTreeIndirect::Tree<2, coord_t>;
+    AABBTree                            m_aabbtree_internal_islands;
+};
+
+} // namespace Slic3r
+
+#endif // slic3r_RetractWhenCrossingPerimeters_hpp_

src/libslic3r/SLAPrintSteps.cpp

@@ -413,6 +413,8 @@ void SLAPrint::Steps::drill_holes(SLAPrintObject &po)
                     [&part_to_drill, &hollowed_mesh](const auto& node)
         {
             part_to_drill.indices.emplace_back(hollowed_mesh.its.indices[node.idx]);
+            // continue traversal
+            return true;
         });
 
         auto cgal_meshpart = MeshBoolean::cgal::triangle_mesh_to_cgal(