Merge pull request #27 from Prusa-Development/pm_anchor_bridges_on_sparse_infill

Ensuring + anchoring bridges over sparse infill

src/clipper/clipper.cpp

@@ -4109,19 +4109,40 @@ void AddPolyNodeToPaths(const PolyNode& polynode, NodeType nodetype, Paths& path
   for (int i = 0; i < polynode.ChildCount(); ++i)
     AddPolyNodeToPaths(*polynode.Childs[i], nodetype, paths);
 }
+
+void AddPolyNodeToPaths(PolyNode&& polynode, NodeType nodetype, Paths& paths)
+{
+  bool match = true;
+  if (nodetype == ntClosed) match = !polynode.IsOpen();
+  else if (nodetype == ntOpen) return;
+
+  if (!polynode.Contour.empty() && match)
+    paths.push_back(std::move(polynode.Contour));
+  for (int i = 0; i < polynode.ChildCount(); ++i)
+    AddPolyNodeToPaths(std::move(*polynode.Childs[i]), nodetype, paths);
+}
+
 //------------------------------------------------------------------------------
 
 void PolyTreeToPaths(const PolyTree& polytree, Paths& paths)
 {
-  paths.resize(0); 
+  paths.clear();
   paths.reserve(polytree.Total());
   AddPolyNodeToPaths(polytree, ntAny, paths);
 }
+
+void PolyTreeToPaths(PolyTree&& polytree, Paths& paths)
+{
+  paths.clear();
+  paths.reserve(polytree.Total());
+  AddPolyNodeToPaths(std::move(polytree), ntAny, paths);
+}
+
 //------------------------------------------------------------------------------
 
 void ClosedPathsFromPolyTree(const PolyTree& polytree, Paths& paths)
 {
-  paths.resize(0); 
+  paths.clear();
   paths.reserve(polytree.Total());
   AddPolyNodeToPaths(polytree, ntClosed, paths);
 }
@@ -4129,7 +4150,7 @@ void ClosedPathsFromPolyTree(const PolyTree& polytree, Paths& paths)
 
 void OpenPathsFromPolyTree(PolyTree& polytree, Paths& paths)
 {
-  paths.resize(0); 
+  paths.clear();
   paths.reserve(polytree.Total());
   //Open paths are top level only, so ...
   for (int i = 0; i < polytree.ChildCount(); ++i)

src/clipper/clipper.hpp

@@ -206,6 +206,7 @@ void MinkowskiSum(const Path& pattern, const Paths& paths, Paths& solution, bool
 void MinkowskiDiff(const Path& poly1, const Path& poly2, Paths& solution);
 
 void PolyTreeToPaths(const PolyTree& polytree, Paths& paths);
+void PolyTreeToPaths(PolyTree&& polytree, Paths& paths);
 void ClosedPathsFromPolyTree(const PolyTree& polytree, Paths& paths);
 void OpenPathsFromPolyTree(PolyTree& polytree, Paths& paths);
 

src/libslic3r/AABBTreeIndirect.hpp

@@ -13,6 +13,7 @@
 
 #include <Eigen/Geometry>
 
+#include "BoundingBox.hpp"
 #include "Utils.hpp" // for next_highest_power_of_2()
 
 // Definition of the ray intersection hit structure.
@@ -217,6 +218,23 @@ using Tree3f = Tree<3, float>;
 using Tree2d = Tree<2, double>;
 using Tree3d = Tree<3, double>;
 
+// Wrap a 2D Slic3r own BoundingBox to be passed to Tree::build() and similar
+// to build an AABBTree over coord_t 2D bounding boxes.
+class BoundingBoxWrapper {
+public:
+	using BoundingBox = Eigen::AlignedBox<coord_t, 2>;
+	BoundingBoxWrapper(const size_t idx, const Slic3r::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 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;
+    BoundingBox		   m_bbox;
+};
+
 namespace detail {
 	template<typename AVertexType, typename AIndexedFaceType, typename ATreeType, typename AVectorType>
 	struct RayIntersector {

src/libslic3r/Algorithm/RegionExpansion.cpp

@@ -0,0 +1,539 @@
+#include "RegionExpansion.hpp"
+
+#include <libslic3r/AABBTreeIndirect.hpp>
+#include <libslic3r/ClipperZUtils.hpp>
+#include <libslic3r/ClipperUtils.hpp>
+#include <libslic3r/Utils.hpp>
+
+#include <numeric>
+
+namespace Slic3r {
+namespace Algorithm {
+
+// Calculating radius discretization according to ClipperLib offsetter code, see void ClipperOffset::DoOffset(double delta)
+inline double clipper_round_offset_error(double offset, double arc_tolerance)
+{
+    static constexpr const double def_arc_tolerance = 0.25;
+    const double y =
+        arc_tolerance <= 0 ?
+            def_arc_tolerance :
+            arc_tolerance > offset * def_arc_tolerance ?
+                offset * def_arc_tolerance :
+                arc_tolerance;
+    double steps = std::min(M_PI / std::acos(1. - y / offset), offset * M_PI);
+    return offset * (1. - cos(M_PI / steps));
+}
+
+RegionExpansionParameters RegionExpansionParameters::build(
+    // Scaled expansion value
+    float                full_expansion,
+    // Expand by waves of expansion_step size (expansion_step is scaled).
+    float                expansion_step,
+    // Don't take more than max_nr_steps for small expansion_step.
+    size_t               max_nr_expansion_steps)
+{
+    assert(full_expansion > 0);
+    assert(expansion_step > 0);
+    assert(max_nr_expansion_steps > 0);
+
+    RegionExpansionParameters out;
+    // Initial expansion of src to make the source regions intersect with boundary regions just a bit.
+    // The expansion should not be too tiny, but also small enough, so the following expansion will
+    // compensate for tiny_expansion and bring the wave back to the boundary without producing
+    // ugly cusps where it touches the boundary.
+    out.tiny_expansion = std::min(0.25f * full_expansion, scaled<float>(0.05f));
+    size_t nsteps = size_t(ceil((full_expansion - out.tiny_expansion) / expansion_step));
+    if (max_nr_expansion_steps > 0)
+        nsteps = std::min(nsteps, max_nr_expansion_steps);
+    assert(nsteps > 0);
+    out.initial_step = (full_expansion - out.tiny_expansion) / nsteps;
+    if (nsteps > 1 && 0.25 * out.initial_step < out.tiny_expansion) {
+        // Decrease the step size by lowering number of steps.
+        nsteps       = std::max<size_t>(1, (floor((full_expansion - out.tiny_expansion) / (4. * out.tiny_expansion))));
+        out.initial_step = (full_expansion - out.tiny_expansion) / nsteps;
+    }
+    if (0.25 * out.initial_step < out.tiny_expansion || nsteps == 1) {
+        out.tiny_expansion = 0.2f * full_expansion;
+        out.initial_step   = 0.8f * full_expansion;
+    }
+    out.other_step           = out.initial_step;
+    out.num_other_steps      = nsteps - 1;
+
+    // Accuracy of the offsetter for wave propagation.
+    out.arc_tolerance        = scaled<double>(0.1);
+    out.shortest_edge_length = out.initial_step * ClipperOffsetShortestEdgeFactor;
+
+    // Maximum inflation of seed contours over the boundary. Used to trim boundary to speed up
+    // clipping during wave propagation. Needs to be in sync with the offsetter accuracy.
+    // Clipper positive round offset should rather offset less than more.
+    // Still a little bit of additional offset was added.
+    out.max_inflation = (out.tiny_expansion + nsteps * out.initial_step) * 1.1;
+//                (clipper_round_offset_error(out.tiny_expansion, co.ArcTolerance) + nsteps * clipper_round_offset_error(out.initial_step, co.ArcTolerance) * 1.5; // Account for uncertainty 
+
+    return out;
+}
+
+// similar to expolygons_to_zpaths(), but each contour is expanded before converted to zpath.
+// The expanded contours are then opened (the first point is repeated at the end).
+static ClipperLib_Z::Paths expolygons_to_zpaths_expanded_opened(
+    const ExPolygons &src, const float expansion, coord_t &base_idx)
+{
+    ClipperLib_Z::Paths out;
+    out.reserve(2 * std::accumulate(src.begin(), src.end(), size_t(0),
+        [](const size_t acc, const ExPolygon &expoly) { return acc + expoly.num_contours(); }));
+    ClipperLib::ClipperOffset offsetter;
+    offsetter.ShortestEdgeLength = expansion * ClipperOffsetShortestEdgeFactor;
+    ClipperLib::Paths expansion_cache;
+    for (const ExPolygon &expoly : src) {
+        for (size_t icontour = 0; icontour < expoly.num_contours(); ++ icontour) {
+            // Execute reorients the contours so that the outer most contour has a positive area. Thus the output
+            // contours will be CCW oriented even though the input paths are CW oriented.
+            // Offset is applied after contour reorientation, thus the signum of the offset value is reversed.
+            offsetter.Clear();
+            offsetter.AddPath(expoly.contour_or_hole(icontour).points, ClipperLib::jtSquare, ClipperLib::etClosedPolygon);
+            expansion_cache.clear();
+            offsetter.Execute(expansion_cache, icontour == 0 ? expansion : -expansion);
+            append(out, ClipperZUtils::to_zpaths<true>(expansion_cache, base_idx));
+        }
+        ++ base_idx;
+    }
+    return out;
+}
+
+// Paths were created by splitting closed polygons into open paths and then by clipping them.
+// Thus some pieces of the clipped polygons may now become split at the ends of the source polygons.
+// Those ends are sorted lexicographically in "splits".
+// Reconnect those split pieces.
+static inline void merge_splits(ClipperLib_Z::Paths &paths, std::vector<std::pair<ClipperLib_Z::IntPoint, int>> &splits)
+{
+    for (auto it_path = paths.begin(); it_path != paths.end(); ) {
+        ClipperLib_Z::Path &path = *it_path;
+        assert(path.size() >= 2);
+        bool merged = false;
+        if (path.size() >= 2) {
+            const ClipperLib_Z::IntPoint &front = path.front();
+            const ClipperLib_Z::IntPoint &back  = path.back();
+            // The path before clipping was supposed to cross the clipping boundary or be fully out of it.
+            // Thus the clipped contour is supposed to become open, with one exception: The anchor expands into a closed hole.
+            if (front.x() != back.x() || front.y() != back.y()) {
+                // Look up the ends in "splits", possibly join the contours.
+                // "splits" maps into the other piece connected to the same end point.
+                auto find_end = [&splits](const ClipperLib_Z::IntPoint &pt) -> std::pair<ClipperLib_Z::IntPoint, int>* {
+                    auto it = std::lower_bound(splits.begin(), splits.end(), pt,
+                        [](const auto &l, const auto &r){ return ClipperZUtils::zpoint_lower(l.first, r); });
+                    return it != splits.end() && it->first == pt ? &(*it) : nullptr;
+                };
+                auto *end = find_end(front);
+                bool  end_front = true;
+                if (! end) {
+                    end_front = false;
+                    end = find_end(back);
+                }
+                if (end) {
+                    // This segment ends at a split point of the source closed contour before clipping.
+                    if (end->second == -1) {
+                        // Open end was found, not matched yet.
+                        end->second = int(it_path - paths.begin());
+                    } else {
+                        // Open end was found and matched with end->second
+                        ClipperLib_Z::Path &other_path = paths[end->second];
+                        polylines_merge(other_path, other_path.front() == end->first, std::move(path), end_front);
+                        if (std::next(it_path) == paths.end()) {
+                            paths.pop_back();
+                            break;
+                        }
+                        path = std::move(paths.back());
+                        paths.pop_back();
+                        merged = true;
+                    }
+                }
+            }
+        }
+        if (! merged)
+            ++ it_path;
+    }
+}
+
+using AABBTreeBBoxes = AABBTreeIndirect::Tree<2, coord_t>;
+
+static AABBTreeBBoxes build_aabb_tree_over_expolygons(const ExPolygons &expolygons) 
+{
+    // Calculate bounding boxes of internal slices.
+    std::vector<AABBTreeIndirect::BoundingBoxWrapper> bboxes;
+    bboxes.reserve(expolygons.size());
+    for (size_t i = 0; i < expolygons.size(); ++ i)
+        bboxes.emplace_back(i, get_extents(expolygons[i].contour));
+    // Build AABB tree over bounding boxes of boundary expolygons.
+    AABBTreeBBoxes out;
+    out.build_modify_input(bboxes);
+    return out;
+}
+
+static int sample_in_expolygons(
+    // AABB tree over boundary expolygons
+    const AABBTreeBBoxes &aabb_tree, 
+    const ExPolygons     &expolygons,
+    const Point          &sample)
+{
+    int out = -1;
+    AABBTreeIndirect::traverse(aabb_tree,
+        [&sample](const AABBTreeBBoxes::Node &node) {
+            return node.bbox.contains(sample);
+        },
+        [&expolygons, &sample, &out](const AABBTreeBBoxes::Node &node) {
+            assert(node.is_leaf());
+            assert(node.is_valid());
+            if (expolygons[node.idx].contains(sample)) {
+                out = int(node.idx);
+                // Stop traversal.
+                return false;
+            }
+            // Continue traversal.
+            return true;
+        });
+    return out;
+}
+
+std::vector<WaveSeed> wave_seeds(
+    // Source regions that are supposed to touch the boundary.
+    const ExPolygons      &src,
+    // Boundaries of source regions touching the "boundary" regions will be expanded into the "boundary" region.
+    const ExPolygons      &boundary,
+    // Initial expansion of src to make the source regions intersect with boundary regions just a bit.
+    float                  tiny_expansion,
+    // Sort output by boundary ID and source ID.
+    bool                   sorted)
+{
+    assert(tiny_expansion > 0);
+
+    if (src.empty())
+        return {};
+
+    using Intersection  = ClipperZUtils::ClipperZIntersectionVisitor::Intersection;
+    using Intersections = ClipperZUtils::ClipperZIntersectionVisitor::Intersections;
+
+    ClipperLib_Z::Paths segments;
+    Intersections       intersections;
+
+    coord_t             idx_boundary_begin = 1;
+    coord_t             idx_boundary_end   = idx_boundary_begin;
+    coord_t             idx_src_end;
+
+    {
+        ClipperLib_Z::Clipper zclipper;
+        ClipperZUtils::ClipperZIntersectionVisitor visitor(intersections);
+        zclipper.ZFillFunction(visitor.clipper_callback());
+        // as closed contours
+        zclipper.AddPaths(ClipperZUtils::expolygons_to_zpaths(boundary, idx_boundary_end), ClipperLib_Z::ptClip, true);
+        // as open contours
+        std::vector<std::pair<ClipperLib_Z::IntPoint, int>> zsrc_splits;
+        {
+            idx_src_end = idx_boundary_end;
+            ClipperLib_Z::Paths zsrc = expolygons_to_zpaths_expanded_opened(src, tiny_expansion, idx_src_end);
+            zclipper.AddPaths(zsrc, ClipperLib_Z::ptSubject, false);
+            zsrc_splits.reserve(zsrc.size());
+            for (const ClipperLib_Z::Path &path : zsrc) {
+                assert(path.size() >= 2);
+                assert(path.front() == path.back());
+                zsrc_splits.emplace_back(path.front(), -1);
+            }
+            std::sort(zsrc_splits.begin(), zsrc_splits.end(), [](const auto &l, const auto &r){ return ClipperZUtils::zpoint_lower(l.first, r.first); });
+        }
+        ClipperLib_Z::PolyTree polytree;
+        zclipper.Execute(ClipperLib_Z::ctIntersection, polytree, ClipperLib_Z::pftNonZero, ClipperLib_Z::pftNonZero);
+        ClipperLib_Z::PolyTreeToPaths(std::move(polytree), segments);
+        merge_splits(segments, zsrc_splits);
+    }
+
+    // AABBTree over bounding boxes of boundaries.
+    // Only built if necessary, that is if any of the seed contours is closed, thus there is no intersection point
+    // with the boundary and all Z coordinates of the closed contour point to the source contour.
+    AABBTreeBBoxes aabb_tree;
+
+    // Sort paths into their respective islands.
+    // Each src x boundary will be processed (wave expanded) independently.
+    // Multiple pieces of a single src may intersect the same boundary.
+    WaveSeeds out;
+    out.reserve(segments.size());
+    int iseed = 0;
+    for (const ClipperLib_Z::Path &path : segments) {
+        assert(path.size() >= 2);
+        const ClipperLib_Z::IntPoint &front = path.front();
+        const ClipperLib_Z::IntPoint &back  = path.back();
+        // Both ends of a seed segment are supposed to be inside a single boundary expolygon.
+        // Thus as long as the seed contour is not closed, it should be open at a boundary point.
+        assert((front == back && front.z() >= idx_boundary_end && front.z() < idx_src_end) || 
+            //(front.z() < 0 && back.z() < 0));
+            // Hope that at least one end of an open polyline is clipped by the boundary, thus an intersection point is created.
+            (front.z() < 0 || back.z() < 0));
+        const Intersection *intersection = nullptr;
+        auto intersection_point_valid = [idx_boundary_end, idx_src_end](const Intersection &is) {
+            return is.first >= 1 && is.first < idx_boundary_end &&
+                   is.second >= idx_boundary_end && is.second < idx_src_end;
+        };
+        if (front.z() < 0) {
+            const Intersection &is = intersections[- front.z() - 1];
+            assert(intersection_point_valid(is));
+            if (intersection_point_valid(is))
+                intersection = &is;
+        }
+        if (! intersection && back.z() < 0) {
+            const Intersection &is = intersections[- back.z() - 1];
+            assert(intersection_point_valid(is));
+            if (intersection_point_valid(is))
+                intersection = &is;
+        }
+        if (intersection) {
+            // The path intersects the boundary contour at least at one side. 
+            out.push_back({ uint32_t(intersection->second - idx_boundary_end), uint32_t(intersection->first - 1), ClipperZUtils::from_zpath(path) });
+        } else {
+            // This should be a closed contour.
+            assert(front == back && front.z() >= idx_boundary_end && front.z() < idx_src_end);
+            // Find a source boundary expolygon of one sample of this closed path.
+            if (aabb_tree.empty())
+                aabb_tree = build_aabb_tree_over_expolygons(boundary);
+            int boundary_id = sample_in_expolygons(aabb_tree, boundary, Point(front.x(), front.y()));
+            // Boundary that contains the sample point was found.
+            assert(boundary_id >= 0);
+            if (boundary_id >= 0)
+                out.push_back({ uint32_t(front.z() - idx_boundary_end), uint32_t(boundary_id), ClipperZUtils::from_zpath(path) });
+        }
+        ++ iseed;
+    }
+
+    if (sorted)
+        // Sort the seeds by their intersection boundary and source contour.
+        std::sort(out.begin(), out.end(), lower_by_boundary_and_src);
+    return out;
+}
+
+static ClipperLib::Paths wavefront_initial(ClipperLib::ClipperOffset &co, const ClipperLib::Paths &polylines, float offset)
+{
+    ClipperLib::Paths out;
+    out.reserve(polylines.size());
+    ClipperLib::Paths out_this;
+    for (const ClipperLib::Path &path : polylines) {
+        assert(path.size() >= 2);
+        co.Clear();
+        co.AddPath(path, jtRound, path.front() == path.back() ? ClipperLib::etClosedLine : ClipperLib::etOpenRound);
+        co.Execute(out_this, offset);
+        append(out, std::move(out_this));
+    }
+    return out;
+}
+
+// Input polygons may consist of multiple expolygons, even nested expolygons.
+// After inflation some polygons may thus overlap, however the overlap is being resolved during the successive
+// clipping operation, thus it is not being done here.
+static ClipperLib::Paths wavefront_step(ClipperLib::ClipperOffset &co, const ClipperLib::Paths &polygons, float offset)
+{
+    ClipperLib::Paths out;
+    out.reserve(polygons.size());
+    ClipperLib::Paths out_this;
+    for (const ClipperLib::Path &polygon : polygons) {
+        co.Clear();
+        // Execute reorients the contours so that the outer most contour has a positive area. Thus the output
+        // contours will be CCW oriented even though the input paths are CW oriented.
+        // Offset is applied after contour reorientation, thus the signum of the offset value is reversed.
+        co.AddPath(polygon, jtRound, ClipperLib::etClosedPolygon);
+        bool ccw = ClipperLib::Orientation(polygon);
+        co.Execute(out_this, ccw ? offset : - offset);
+        if (! ccw) {
+            // Reverse the resulting contours.
+            for (ClipperLib::Path &path : out_this)
+                std::reverse(path.begin(), path.end());
+        }
+        append(out, std::move(out_this));
+    }
+    return out;
+}
+
+static ClipperLib::Paths wavefront_clip(const ClipperLib::Paths &wavefront, const Polygons &clipping)
+{
+    ClipperLib::Clipper clipper;
+    clipper.AddPaths(wavefront, ClipperLib::ptSubject, true);
+    clipper.AddPaths(ClipperUtils::PolygonsProvider(clipping),  ClipperLib::ptClip, true);
+    ClipperLib::Paths out;
+    clipper.Execute(ClipperLib::ctIntersection, out, ClipperLib::pftPositive, ClipperLib::pftPositive);
+    return out;
+}
+
+static Polygons propagate_wave_from_boundary(
+    ClipperLib::ClipperOffset   &co,
+    // Seed of the wave: Open polylines very close to the boundary.
+    const ClipperLib::Paths     &seed,
+    // Boundary inside which the waveform will propagate.
+    const ExPolygon             &boundary,
+    // How much to inflate the seed lines to produce the first wave area.
+    const float                  initial_step,
+    // How much to inflate the first wave area and the successive wave areas in each step.
+    const float                  other_step,
+    // Number of inflate steps after the initial step.
+    const size_t                 num_other_steps,
+    // Maximum inflation of seed contours over the boundary. Used to trim boundary to speed up
+    // clipping during wave propagation.
+    const float                  max_inflation)
+{
+    assert(! seed.empty() && seed.front().size() >= 2);
+    Polygons clipping = ClipperUtils::clip_clipper_polygons_with_subject_bbox(boundary, get_extents<true>(seed).inflated(max_inflation));
+    ClipperLib::Paths polygons = wavefront_clip(wavefront_initial(co, seed, initial_step), clipping);
+    // Now offset the remaining 
+    for (size_t ioffset = 0; ioffset < num_other_steps; ++ ioffset)
+        polygons = wavefront_clip(wavefront_step(co, polygons, other_step), clipping);
+    return to_polygons(polygons);
+}
+
+// Resulting regions are sorted by boundary id and source id.
+std::vector<RegionExpansion> propagate_waves(const WaveSeeds &seeds, const ExPolygons &boundary, const RegionExpansionParameters &params)
+{
+    std::vector<RegionExpansion> out;
+    ClipperLib::Paths            paths;
+    ClipperLib::ClipperOffset co;
+    co.ArcTolerance       = params.arc_tolerance;
+    co.ShortestEdgeLength = params.shortest_edge_length;
+    for (auto it_seed = seeds.begin(); it_seed != seeds.end();) {
+        auto it = it_seed;
+        paths.clear();
+        for (; it != seeds.end() && it->boundary == it_seed->boundary && it->src == it_seed->src; ++ it)
+            paths.emplace_back(it->path);
+        // Propagate the wavefront while clipping it with the trimmed boundary.
+        // Collect the expanded polygons, merge them with the source polygons.
+        RegionExpansion re;
+        for (Polygon &polygon : propagate_wave_from_boundary(co, paths, boundary[it_seed->boundary], params.initial_step, params.other_step, params.num_other_steps, params.max_inflation))
+            out.push_back({ std::move(polygon), it_seed->src, it_seed->boundary });
+        it_seed = it;
+    }
+
+    return out;
+}
+
+std::vector<RegionExpansion> propagate_waves(const ExPolygons &src, const ExPolygons &boundary, const RegionExpansionParameters &params)
+{
+    return propagate_waves(wave_seeds(src, boundary, params.tiny_expansion, true), boundary, params);
+}
+
+std::vector<RegionExpansion> propagate_waves(const ExPolygons &src, const ExPolygons &boundary,
+    // Scaled expansion value
+    float expansion, 
+    // Expand by waves of expansion_step size (expansion_step is scaled).
+    float expansion_step,
+    // Don't take more than max_nr_steps for small expansion_step.
+    size_t max_nr_steps)
+{
+    return propagate_waves(src, boundary, RegionExpansionParameters::build(expansion, expansion_step, max_nr_steps));
+}
+
+// Returns regions per source ExPolygon expanded into boundary.
+std::vector<RegionExpansionEx> propagate_waves_ex(const WaveSeeds &seeds, const ExPolygons &boundary, const RegionExpansionParameters &params)
+{
+    std::vector<RegionExpansion> expanded = propagate_waves(seeds, boundary, params);
+    assert(std::is_sorted(seeds.begin(), seeds.end(), [](const auto &l, const auto &r){ return l.boundary < r.boundary || (l.boundary == r.boundary && l.src < r.src); }));
+    Polygons acc;
+    std::vector<RegionExpansionEx> out;
+    for (auto it = expanded.begin(); it != expanded.end(); ) {
+        auto it2 = it;
+        acc.clear();
+        for (; it2 != expanded.end() && it2->boundary_id == it->boundary_id && it2->src_id == it->src_id; ++ it2)
+            acc.emplace_back(std::move(it2->polygon));
+        size_t size = it2 - it;
+        if (size == 1)
+            out.push_back({ ExPolygon{std::move(acc.front())}, it->src_id, it->boundary_id });
+        else {
+            ExPolygons expolys = union_ex(acc);
+            reserve_more_power_of_2(out, expolys.size());
+            for (ExPolygon &ex : expolys)
+                out.push_back({ std::move(ex), it->src_id, it->boundary_id });
+        }
+        it = it2;
+    }
+    return out;
+}
+
+// Returns regions per source ExPolygon expanded into boundary.
+std::vector<RegionExpansionEx> propagate_waves_ex(
+    // Source regions that are supposed to touch the boundary.
+    // Boundaries of source regions touching the "boundary" regions will be expanded into the "boundary" region.
+    const ExPolygons    &src,
+    const ExPolygons    &boundary,
+    // Scaled expansion value
+    float                full_expansion,
+    // Expand by waves of expansion_step size (expansion_step is scaled).
+    float                expansion_step,
+    // Don't take more than max_nr_steps for small expansion_step.
+    size_t               max_nr_expansion_steps)
+{
+    auto params = RegionExpansionParameters::build(full_expansion, expansion_step, max_nr_expansion_steps);
+    return propagate_waves_ex(wave_seeds(src, boundary, params.tiny_expansion, true), boundary, params);
+}
+
+std::vector<Polygons> expand_expolygons(const ExPolygons &src, const ExPolygons &boundary,
+    // Scaled expansion value
+    float expansion, 
+    // Expand by waves of expansion_step size (expansion_step is scaled).
+    float expansion_step,
+    // Don't take more than max_nr_steps for small expansion_step.
+    size_t max_nr_steps)
+{
+    std::vector<Polygons> out(src.size(), Polygons{});
+    for (RegionExpansion &r : propagate_waves(src, boundary, expansion, expansion_step, max_nr_steps))
+        out[r.src_id].emplace_back(std::move(r.polygon));
+    return out;
+}
+
+std::vector<ExPolygon> expand_merge_expolygons(ExPolygons &&src, const ExPolygons &boundary, const RegionExpansionParameters &params)
+{
+    // expanded regions are sorted by boundary id and source id
+    std::vector<RegionExpansion> expanded = propagate_waves(src, boundary, params);
+    // expanded regions will be merged into source regions, thus they will be re-sorted by source id.
+    std::sort(expanded.begin(), expanded.end(), [](const auto &l, const auto &r) { return l.src_id < r.src_id; });
+    uint32_t   last = 0;
+    Polygons   acc;
+    ExPolygons out;
+    out.reserve(src.size());
+    for (auto it = expanded.begin(); it != expanded.end();) {
+        for (; last < it->src_id; ++ last)
+            out.emplace_back(std::move(src[last]));
+        acc.clear();
+        assert(it->src_id == last);
+        for (; it != expanded.end() && it->src_id == last; ++ it)
+            acc.emplace_back(std::move(it->polygon));
+        //FIXME offset & merging could be more efficient, for example one does not need to copy the source expolygon
+        ExPolygon &src_ex = src[last ++];
+        assert(! src_ex.contour.empty());
+#if 0
+        {
+            static int iRun = 0;
+            BoundingBox bbox = get_extents(acc);
+            bbox.merge(get_extents(src_ex));
+            SVG svg(debug_out_path("expand_merge_expolygons-failed-union=%d.svg", iRun ++).c_str(), bbox);
+            svg.draw(acc);
+            svg.draw_outline(acc, "black", scale_(0.05));
+            svg.draw(src_ex, "red");
+            svg.Close();
+        }
+#endif
+        Point sample = src_ex.contour.front();
+        append(acc, to_polygons(std::move(src_ex)));
+        ExPolygons merged = union_safety_offset_ex(acc);
+        // Expanding one expolygon by waves should not change connectivity of the source expolygon:
+        // Single expolygon should be produced possibly with increased number of holes.
+        if (merged.size() > 1) {
+            // assert(merged.size() == 1);
+            // There is something wrong with the initial waves. Most likely the bridge was not valid at all
+            // or the boundary region was very close to some bridge edge, but not really touching.
+            // Pick only a single merged expolygon, which contains one sample point of the source expolygon.
+            auto aabb_tree = build_aabb_tree_over_expolygons(merged);
+            int id = sample_in_expolygons(aabb_tree, merged, sample);
+            assert(id != -1);
+            if (id != -1)
+                out.emplace_back(std::move(merged[id]));
+        } else if (merged.size() == 1)
+            out.emplace_back(std::move(merged.front()));
+    }
+    for (; last < uint32_t(src.size()); ++ last)
+        out.emplace_back(std::move(src[last]));
+    return out;
+}
+
+} // Algorithm
+} // Slic3r

src/libslic3r/Algorithm/RegionExpansion.hpp

@@ -0,0 +1,114 @@
+#ifndef SRC_LIBSLIC3R_ALGORITHM_REGION_EXPANSION_HPP_
+#define SRC_LIBSLIC3R_ALGORITHM_REGION_EXPANSION_HPP_
+
+#include <cstdint>
+#include <libslic3r/Point.hpp>
+#include <libslic3r/Polygon.hpp>
+#include <libslic3r/ExPolygon.hpp>
+
+namespace Slic3r {
+namespace Algorithm {
+
+struct RegionExpansionParameters
+{
+    // Initial expansion of src to make the source regions intersect with boundary regions just a bit.
+    float                  tiny_expansion;
+    // How much to inflate the seed lines to produce the first wave area.
+    float                  initial_step;
+    // How much to inflate the first wave area and the successive wave areas in each step.
+    float                  other_step;
+    // Number of inflate steps after the initial step.
+    size_t                 num_other_steps;
+    // Maximum inflation of seed contours over the boundary. Used to trim boundary to speed up
+    // clipping during wave propagation.
+    float                  max_inflation;
+
+    // Accuracy of the offsetter for wave propagation.
+    double                 arc_tolerance;
+    double                 shortest_edge_length;
+
+    static RegionExpansionParameters build(
+        // Scaled expansion value
+        float                full_expansion,
+        // Expand by waves of expansion_step size (expansion_step is scaled).
+        float                expansion_step,
+        // Don't take more than max_nr_steps for small expansion_step.
+        size_t               max_nr_expansion_steps);
+};
+
+struct WaveSeed {
+    uint32_t src;
+    uint32_t boundary;
+    Points   path;
+};
+using WaveSeeds = std::vector<WaveSeed>;
+
+inline bool lower_by_boundary_and_src(const WaveSeed &l, const WaveSeed &r)
+{
+    return l.boundary < r.boundary || (l.boundary == r.boundary && l.src < r.src);
+}
+
+inline bool lower_by_src_and_boundary(const WaveSeed &l, const WaveSeed &r)
+{
+    return l.src < r.src || (l.src == r.src && l.boundary < r.boundary);
+}
+
+// Expand src slightly outwards to intersect boundaries, trim the offsetted src polylines by the boundaries.
+// Return the trimmed paths annotated with their origin (source of the path, index of the boundary region).
+WaveSeeds wave_seeds(
+    // Source regions that are supposed to touch the boundary.
+    const ExPolygons      &src,
+    // Boundaries of source regions touching the "boundary" regions will be expanded into the "boundary" region.
+    const ExPolygons      &boundary,
+    // Initial expansion of src to make the source regions intersect with boundary regions just a bit.
+    float                  tiny_expansion,
+    bool                   sorted);
+
+struct RegionExpansion
+{
+    Polygon     polygon;
+    uint32_t    src_id;
+    uint32_t    boundary_id;
+};
+
+std::vector<RegionExpansion> propagate_waves(const WaveSeeds &seeds, const ExPolygons &boundary, const RegionExpansionParameters &params);
+
+std::vector<RegionExpansion> propagate_waves(const ExPolygons &src, const ExPolygons &boundary,
+    // Scaled expansion value
+    float expansion, 
+    // Expand by waves of expansion_step size (expansion_step is scaled).
+    float expansion_step,
+    // Don't take more than max_nr_steps for small expansion_step.
+    size_t max_nr_steps);
+
+struct RegionExpansionEx
+{
+    ExPolygon   expolygon;
+    uint32_t    src_id;
+    uint32_t    boundary_id;
+};
+
+std::vector<RegionExpansionEx> propagate_waves_ex(const WaveSeeds &seeds, const ExPolygons &boundary, const RegionExpansionParameters &params);
+
+std::vector<RegionExpansionEx> propagate_waves_ex(const ExPolygons &src, const ExPolygons &boundary,
+    // Scaled expansion value
+    float expansion, 
+    // Expand by waves of expansion_step size (expansion_step is scaled).
+    float expansion_step,
+    // Don't take more than max_nr_steps for small expansion_step.
+    size_t max_nr_steps);
+
+std::vector<Polygons> expand_expolygons(const ExPolygons &src, const ExPolygons &boundary,
+    // Scaled expansion value
+    float expansion, 
+    // Expand by waves of expansion_step size (expansion_step is scaled).
+    float expansion_step,
+    // Don't take more than max_nr_steps for small expansion_step.
+    size_t max_nr_steps);
+
+std::vector<ExPolygon> expand_merge_expolygons(ExPolygons &&src, const ExPolygons &boundary, const RegionExpansionParameters &params);
+
+} // Algorithm
+} // Slic3r
+
+#endif /* SRC_LIBSLIC3R_ALGORITHM_REGION_EXPANSION_HPP_ */

src/libslic3r/BoundingBox.hpp

@@ -22,24 +22,9 @@ public:
     BoundingBoxBase(const PointClass &p1, const PointClass &p2, const PointClass &p3) :
         min(p1), max(p1), defined(false) { merge(p2); merge(p3); }
 
-    template<class It, class = IteratorOnly<It> >
+    template<class It, class = IteratorOnly<It>>
-    BoundingBoxBase(It from, It to) : min(PointClass::Zero()), max(PointClass::Zero())
+    BoundingBoxBase(It from, It to)
-    {
+        { construct(*this, from, to); }
-        if (from == to) {
-            this->defined = false;
-            // throw Slic3r::InvalidArgument("Empty point set supplied to BoundingBoxBase constructor");
-        } else {
-            auto it = from;
-            this->min = it->template cast<typename PointClass::Scalar>();
-            this->max = this->min;
-            for (++ it; it != to; ++ it) {
-                auto vec = it->template cast<typename PointClass::Scalar>();
-                this->min = this->min.cwiseMin(vec);
-                this->max = this->max.cwiseMax(vec);
-            }
-            this->defined = (this->min.x() < this->max.x()) && (this->min.y() < this->max.y());
-        }
-    }
 
     BoundingBoxBase(const std::vector<PointClass> &points)
         : BoundingBoxBase(points.begin(), points.end())
@@ -70,6 +55,30 @@ public:
     }
     bool operator==(const BoundingBoxBase<PointClass> &rhs) { return this->min == rhs.min && this->max == rhs.max; }
     bool operator!=(const BoundingBoxBase<PointClass> &rhs) { return ! (*this == rhs); }
+
+private:
+    // to access construct()
+    friend BoundingBox get_extents<false>(const Points &pts);
+    friend BoundingBox get_extents<true>(const Points &pts);
+
+    // if IncludeBoundary, then a bounding box is defined even for a single point.
+    // otherwise a bounding box is only defined if it has a positive area.
+    // The output bounding box is expected to be set to "undefined" initially.
+    template<bool IncludeBoundary = false, class BoundingBoxType, class It, class = IteratorOnly<It>>
+    static void construct(BoundingBoxType &out, It from, It to)
+    {
+        if (from != to) {
+            auto it = from;
+            out.min = it->template cast<typename PointClass::Scalar>();
+            out.max = out.min;
+            for (++ it; it != to; ++ it) {
+                auto vec = it->template cast<typename PointClass::Scalar>();
+                out.min = out.min.cwiseMin(vec);
+                out.max = out.max.cwiseMax(vec);
+            }
+            out.defined = IncludeBoundary || (out.min.x() < out.max.x() && out.min.y() < out.max.y());
+        }
+    }
 };
 
 template <class PointClass>

src/libslic3r/BridgeDetector.hpp

@@ -75,12 +75,9 @@ private:
 
 
 //return ideal bridge direction and unsupported bridge endpoints distance.
-inline std::tuple<Vec2d, double> detect_bridging_direction(const Polygons &to_cover, const Polygons &anchors_area)
+inline std::tuple<Vec2d, double> detect_bridging_direction(const Lines &floating_edges, const Polygons &overhang_area)
 {
-    Polygons  overhang_area      = diff(to_cover, anchors_area);
+    if (floating_edges.empty()) {
-    Polylines floating_polylines = diff_pl(to_polylines(overhang_area), expand(anchors_area, float(SCALED_EPSILON)));
-
-    if (floating_polylines.empty()) {
         // consider this area anchored from all sides, pick bridging direction that will likely yield shortest bridges
         auto [pc1, pc2] = compute_principal_components(overhang_area);
         if (pc2 == Vec2f::Zero()) { // overhang may be smaller than resolution. In this case, any direction is ok
@@ -91,7 +88,6 @@ inline std::tuple<Vec2d, double> detect_bridging_direction(const Polygons &to_co
     }
 
     // Overhang is not fully surrounded by anchors, in that case, find such direction that will minimize the number of bridge ends/180turns in the air
-    Lines     floating_edges     = to_lines(floating_polylines);
     std::unordered_map<double, Vec2d> directions{};
     for (const Line &l : floating_edges) {
         Vec2d normal = l.normal().cast<double>().normalized();
@@ -125,6 +121,13 @@ inline std::tuple<Vec2d, double> detect_bridging_direction(const Polygons &to_co
     return {result_dir, min_cost};
 };
 
+//return ideal bridge direction and unsupported bridge endpoints distance.
+inline std::tuple<Vec2d, double> detect_bridging_direction(const Polygons &to_cover, const Polygons &anchors_area)
+{
+    Polygons  overhang_area      = diff(to_cover, anchors_area);
+    Lines     floating_edges     = to_lines(diff_pl(to_polylines(overhang_area), expand(anchors_area, float(SCALED_EPSILON))));
+    return detect_bridging_direction(floating_edges, overhang_area);
+}
 
 }
 

src/libslic3r/Brim.cpp

@@ -641,7 +641,7 @@ ExtrusionEntityCollection make_brim(const Print &print, PrintTryCancel try_cance
 			// perform operation
 			ClipperLib_Z::PolyTree loops_trimmed_tree;
 			clipper.Execute(ClipperLib_Z::ctDifference, loops_trimmed_tree, ClipperLib_Z::pftNonZero, ClipperLib_Z::pftNonZero);
-			ClipperLib_Z::PolyTreeToPaths(loops_trimmed_tree, loops_trimmed);
+			ClipperLib_Z::PolyTreeToPaths(std::move(loops_trimmed_tree), loops_trimmed);
 		}
 
 		// Third, produce the extrusions, sorted by the source loop indices.

src/libslic3r/CMakeLists.txt

@@ -22,6 +22,8 @@ set(SLIC3R_SOURCES
     AABBTreeLines.hpp
     AABBMesh.hpp
     AABBMesh.cpp
+    Algorithm/RegionExpansion.cpp
+    Algorithm/RegionExpansion.hpp
     AnyPtr.hpp
     BoundingBox.cpp
     BoundingBox.hpp
@@ -36,6 +38,7 @@ set(SLIC3R_SOURCES
     clipper.hpp
     ClipperUtils.cpp
     ClipperUtils.hpp
+    ClipperZUtils.hpp
     Color.cpp
     Color.hpp
     Config.cpp
@@ -79,6 +82,8 @@ set(SLIC3R_SOURCES
     Fill/FillBase.hpp
     Fill/FillConcentric.cpp
     Fill/FillConcentric.hpp
+    Fill/FillEnsuring.cpp
+    Fill/FillEnsuring.hpp
     Fill/FillHoneycomb.cpp
     Fill/FillHoneycomb.hpp
     Fill/FillGyroid.cpp

src/libslic3r/ClipperUtils.cpp

@@ -8,8 +8,6 @@
 #include "SVG.hpp"
 #endif /* CLIPPER_UTILS_DEBUG */
 
-#define CLIPPER_OFFSET_SHORTEST_EDGE_FACTOR (0.005f)
-
 namespace Slic3r {
 
 #ifdef CLIPPER_UTILS_DEBUG
@@ -267,7 +265,7 @@ static ClipperLib::Paths raw_offset(PathsProvider &&paths, float offset, Clipper
         co.ArcTolerance = miterLimit;
     else
         co.MiterLimit = miterLimit;
-    co.ShortestEdgeLength = double(std::abs(offset * CLIPPER_OFFSET_SHORTEST_EDGE_FACTOR));
+    co.ShortestEdgeLength = std::abs(offset * ClipperOffsetShortestEdgeFactor);
     for (const ClipperLib::Path &path : paths) {
         co.Clear();
         // Execute reorients the contours so that the outer most contour has a positive area. Thus the output
@@ -414,7 +412,7 @@ static int offset_expolygon_inner(const Slic3r::ExPolygon &expoly, const float d
             co.ArcTolerance = miterLimit;
         else
             co.MiterLimit = miterLimit;
-        co.ShortestEdgeLength = double(std::abs(delta * CLIPPER_OFFSET_SHORTEST_EDGE_FACTOR));
+        co.ShortestEdgeLength = std::abs(delta * ClipperOffsetShortestEdgeFactor);
         co.AddPath(expoly.contour.points, joinType, ClipperLib::etClosedPolygon);
         co.Execute(contours, delta);
     }
@@ -435,7 +433,7 @@ static int offset_expolygon_inner(const Slic3r::ExPolygon &expoly, const float d
                     co.ArcTolerance = miterLimit;
                 else
                     co.MiterLimit = miterLimit;
-                co.ShortestEdgeLength = double(std::abs(delta * CLIPPER_OFFSET_SHORTEST_EDGE_FACTOR));
+                co.ShortestEdgeLength = std::abs(delta * ClipperOffsetShortestEdgeFactor);
                 co.AddPath(hole.points, joinType, ClipperLib::etClosedPolygon);
                 ClipperLib::Paths out2;
                 // Execute reorients the contours so that the outer most contour has a positive area. Thus the output
@@ -720,6 +718,8 @@ Slic3r::ExPolygons diff_ex(const Slic3r::Surfaces &subject, const Slic3r::Surfac
     { return _clipper_ex(ClipperLib::ctDifference, ClipperUtils::SurfacesProvider(subject), ClipperUtils::SurfacesProvider(clip), do_safety_offset); }
 Slic3r::ExPolygons diff_ex(const Slic3r::SurfacesPtr &subject, const Slic3r::Polygons &clip, ApplySafetyOffset do_safety_offset)
     { return _clipper_ex(ClipperLib::ctDifference, ClipperUtils::SurfacesPtrProvider(subject), ClipperUtils::PolygonsProvider(clip), do_safety_offset); }
+Slic3r::ExPolygons diff_ex(const Slic3r::SurfacesPtr &subject, const Slic3r::ExPolygons &clip, ApplySafetyOffset do_safety_offset)
+    { return _clipper_ex(ClipperLib::ctDifference, ClipperUtils::SurfacesPtrProvider(subject), ClipperUtils::ExPolygonsProvider(clip), do_safety_offset); }
 
 Slic3r::ExPolygons intersection_ex(const Slic3r::Polygons &subject, const Slic3r::Polygons &clip, ApplySafetyOffset do_safety_offset)
     { return _clipper_ex(ClipperLib::ctIntersection, ClipperUtils::PolygonsProvider(subject), ClipperUtils::PolygonsProvider(clip), do_safety_offset); }
@@ -1062,7 +1062,7 @@ ClipperLib::Path mittered_offset_path_scaled(const Points &contour, const std::v
 		};
 
 		// Minimum edge length, squared.
-		double lmin  = *std::max_element(deltas.begin(), deltas.end()) * CLIPPER_OFFSET_SHORTEST_EDGE_FACTOR;
+		double lmin  = *std::max_element(deltas.begin(), deltas.end()) * ClipperOffsetShortestEdgeFactor;
 		double l2min = lmin * lmin;
 		// Minimum angle to consider two edges to be parallel.
 		// Vojtech's estimate.

src/libslic3r/ClipperUtils.hpp

@@ -39,6 +39,9 @@ static constexpr const Slic3r::ClipperLib::JoinType DefaultLineJoinType     = Sl
 // Miter limit is ignored for jtSquare.
 static constexpr const double                       DefaultLineMiterLimit   = 0.;
 
+// Decimation factor applied on input contour when doing offset, multiplied by the offset distance.
+static constexpr const double                       ClipperOffsetShortestEdgeFactor = 0.005;
+
 enum class ApplySafetyOffset {
     No,
     Yes
@@ -370,6 +373,8 @@ inline Slic3r::Polygons   shrink(const Slic3r::Polygons &polygons, const float d
     { assert(delta > 0); return offset(polygons, -delta, joinType, miterLimit); }
 inline Slic3r::ExPolygons shrink_ex(const Slic3r::Polygons &polygons, const float delta, ClipperLib::JoinType joinType = DefaultJoinType, double miterLimit = DefaultMiterLimit) 
     { assert(delta > 0); return offset_ex(polygons, -delta, joinType, miterLimit); }
+inline Slic3r::ExPolygons shrink_ex(const Slic3r::ExPolygons &polygons, const float delta, ClipperLib::JoinType joinType = DefaultJoinType, double miterLimit = DefaultMiterLimit) 
+    { assert(delta > 0); return offset_ex(polygons, -delta, joinType, miterLimit); }
 
 // Wherever applicable, please use the opening() / closing() variants instead, they convey their purpose better.
 // Input polygons for negative offset shall be "normalized": There must be no overlap / intersections between the input polygons.
@@ -430,6 +435,7 @@ 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::ExPolygons diff_ex(const Slic3r::SurfacesPtr &subject, const Slic3r::ExPolygons &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);
@@ -601,6 +607,6 @@ Polygons  variable_offset_outer(const ExPolygon &expoly, const std::vector<std::
 ExPolygons variable_offset_outer_ex(const ExPolygon &expoly, const std::vector<std::vector<float>> &deltas, double miter_limit = 2.);
 ExPolygons variable_offset_inner_ex(const ExPolygon &expoly, const std::vector<std::vector<float>> &deltas, double miter_limit = 2.);
 
-}
+} // namespace Slic3r
 
-#endif
+#endif // slic3r_ClipperUtils_hpp_

src/libslic3r/ClipperZUtils.hpp

@@ -0,0 +1,143 @@
+#ifndef slic3r_ClipperZUtils_hpp_
+#define slic3r_ClipperZUtils_hpp_
+
+#include <numeric>
+#include <vector>
+
+#include <clipper/clipper_z.hpp>
+#include <libslic3r/Point.hpp>
+
+namespace Slic3r {
+
+namespace ClipperZUtils {
+
+using ZPoint  = ClipperLib_Z::IntPoint;
+using ZPoints = ClipperLib_Z::Path;
+using ZPath   = ClipperLib_Z::Path;
+using ZPaths  = ClipperLib_Z::Paths;
+
+inline bool zpoint_lower(const ZPoint &l, const ZPoint &r)
+{
+    return l.x() < r.x() || (l.x() == r.x() && (l.y() < r.y() || (l.y() == r.y() && l.z() < r.z())));
+}
+
+// Convert a single path to path with a given Z coordinate.
+// If Open, then duplicate the first point at the end.
+template<bool Open = false>
+inline ZPath to_zpath(const Points &path, coord_t z)
+{
+    ZPath out;
+    if (! path.empty()) {
+        out.reserve((path.size() + Open) ? 1 : 0);
+        for (const Point &p : path)
+            out.emplace_back(p.x(), p.y(), z);
+        if (Open)
+            out.emplace_back(out.front());
+    }
+    return out;
+}
+
+// Convert multiple paths to paths with a given Z coordinate.
+// If Open, then duplicate the first point of each path at its end.
+template<bool Open = false>
+inline ZPaths to_zpaths(const std::vector<Points> &paths, coord_t z)
+{
+    ZPaths out;
+    out.reserve(paths.size());
+    for (const Points &path : paths)
+        out.emplace_back(to_zpath<Open>(path, z));
+    return out;
+}
+
+// Convert multiple expolygons into z-paths with Z specified by an index of the source expolygon
+// offsetted by base_index.
+// If Open, then duplicate the first point of each path at its end.
+template<bool Open = false>
+inline ZPaths expolygons_to_zpaths(const ExPolygons &src, coord_t &base_idx)
+{
+    ZPaths out;
+    out.reserve(std::accumulate(src.begin(), src.end(), size_t(0),
+        [](const size_t acc, const ExPolygon &expoly) { return acc + expoly.num_contours(); }));
+    for (const ExPolygon &expoly : src) {
+        out.emplace_back(to_zpath<Open>(expoly.contour.points, base_idx));
+        for (const Polygon &hole : expoly.holes)
+            out.emplace_back(to_zpath<Open>(hole.points, base_idx));
+        ++ base_idx;
+    }
+    return out;
+}
+
+// Convert a single path to path with a given Z coordinate.
+// If Open, then duplicate the first point at the end.
+template<bool Open = false>
+inline Points from_zpath(const ZPoints &path)
+{
+    Points out;
+    if (! path.empty()) {
+        out.reserve((path.size() + Open) ? 1 : 0);
+        for (const ZPoint &p : path)
+            out.emplace_back(p.x(), p.y());
+        if (Open)
+            out.emplace_back(out.front());
+    }
+    return out;
+}
+
+// Convert multiple paths to paths with a given Z coordinate.
+// If Open, then duplicate the first point of each path at its end.
+template<bool Open = false>
+inline void from_zpaths(const ZPaths &paths, std::vector<Points> &out)
+{
+    out.reserve(out.size() + paths.size());
+    for (const ZPoints &path : paths)
+        out.emplace_back(from_zpath<Open>(path));
+}
+template<bool Open = false>
+inline std::vector<Points> from_zpaths(const ZPaths &paths)
+{
+    std::vector<Points> out;
+    from_zpaths(paths, out);
+    return out;
+}
+
+class ClipperZIntersectionVisitor {
+public:
+    using Intersection  = std::pair<coord_t, coord_t>;
+    using Intersections = std::vector<Intersection>;
+    ClipperZIntersectionVisitor(Intersections &intersections) : m_intersections(intersections) {}
+    void reset() { m_intersections.clear(); }
+    void operator()(const ZPoint &e1bot, const ZPoint &e1top, const ZPoint &e2bot, const ZPoint &e2top, ZPoint &pt) {
+        coord_t srcs[4]{ e1bot.z(), e1top.z(), e2bot.z(), e2top.z() };
+        coord_t *begin = srcs;
+        coord_t *end = srcs + 4;
+        //FIXME bubble sort manually?
+        std::sort(begin, end);
+        end = std::unique(begin, end);
+        if (begin + 1 == end) {
+            // Self intersection may happen on source contour. Just copy the Z value.
+            pt.z() = *begin;
+        } else {
+            assert(begin + 2 == end);
+            if (begin + 2 <= end) {
+                // store a -1 based negative index into the "intersections" vector here.
+                m_intersections.emplace_back(srcs[0], srcs[1]);
+                pt.z() = -coord_t(m_intersections.size());
+            }
+        }
+    }
+    ClipperLib_Z::ZFillCallback clipper_callback() {
+        return [this](const ZPoint &e1bot, const ZPoint &e1top, 
+                 const ZPoint &e2bot, const ZPoint &e2top, ZPoint &pt)
+        { return (*this)(e1bot, e1top, e2bot, e2top, pt); };
+    }
+
+    const std::vector<std::pair<coord_t, coord_t>>& intersections() const { return m_intersections; }
+
+private:
+    std::vector<std::pair<coord_t, coord_t>> &m_intersections;
+};
+
+} // namespace ClipperZUtils
+} // namespace Slic3r
+
+#endif // slic3r_ClipperZUtils_hpp_

src/libslic3r/Config.hpp

@@ -303,7 +303,7 @@ template <class T>
 class ConfigOptionSingle : public ConfigOption {
 public:
     T value;
-    explicit ConfigOptionSingle(T value) : value(value) {}
+    explicit ConfigOptionSingle(T value) : value(std::move(value)) {}
     operator T() const { return this->value; }
     
     void set(const ConfigOption *rhs) override
@@ -847,9 +847,9 @@ using ConfigOptionIntsNullable = ConfigOptionIntsTempl<true>;
 class ConfigOptionString : public ConfigOptionSingle<std::string>
 {
 public:
-    ConfigOptionString() : ConfigOptionSingle<std::string>("") {}
+    ConfigOptionString() : ConfigOptionSingle<std::string>(std::string{}) {}
-    explicit ConfigOptionString(const std::string &value) : ConfigOptionSingle<std::string>(value) {}
+    explicit ConfigOptionString(std::string value) : ConfigOptionSingle<std::string>(std::move(value)) {}
-    
+
     static ConfigOptionType static_type() { return coString; }
     ConfigOptionType        type()  const override { return static_type(); }
     ConfigOption*           clone() const override { return new ConfigOptionString(*this); }

src/libslic3r/Fill/Fill.cpp

@@ -15,10 +15,12 @@
 #include "FillRectilinear.hpp"
 #include "FillLightning.hpp"
 #include "FillConcentric.hpp"
-
+#include "FillEnsuring.hpp"
 
 namespace Slic3r {
 
+static constexpr const float NarrowInfillAreaThresholdMM = 3.f;
+
 struct SurfaceFillParams
 {
 	// Zero based extruder ID.
@@ -159,7 +161,8 @@ std::vector<SurfaceFill> group_fills(const Layer &layer)
 		        // Calculate the actual flow we'll be using for this infill.
 		        params.bridge = is_bridge || Fill::use_bridge_flow(params.pattern);
 				params.flow   = params.bridge ?
-					layerm.bridging_flow(extrusion_role) :
+					// Always enable thick bridges for internal bridges.
+					layerm.bridging_flow(extrusion_role, surface.is_bridge() && ! surface.is_external()) :
 					layerm.flow(extrusion_role, (surface.thickness == -1) ? layer.height : surface.thickness);
 
 				// Calculate flow spacing for infill pattern generation.
@@ -302,6 +305,46 @@ std::vector<SurfaceFill> group_fills(const Layer &layer)
 		}
     }
 
+	// Detect narrow internal solid infill area and use ipEnsuring pattern instead.
+	{
+		std::vector<char> narrow_expolygons;
+		static constexpr const auto narrow_pattern = ipEnsuring;
+		for (size_t surface_fill_id = 0, num_old_fills = surface_fills.size(); surface_fill_id < num_old_fills; ++ surface_fill_id)
+			if (SurfaceFill &fill = surface_fills[surface_fill_id]; fill.surface.surface_type == stInternalSolid) {
+				size_t num_expolygons = fill.expolygons.size();
+				narrow_expolygons.clear();
+				narrow_expolygons.reserve(num_expolygons);
+				// Detect narrow expolygons.
+				int num_narrow = 0;
+				for (const ExPolygon &ex : fill.expolygons) {
+					bool narrow = offset_ex(ex, -scaled<float>(NarrowInfillAreaThresholdMM)).empty();
+					num_narrow += int(narrow);
+					narrow_expolygons.emplace_back(narrow);
+				}
+				if (num_narrow == num_expolygons) {
+					// All expolygons are narrow, change the fill pattern.
+					fill.params.pattern = narrow_pattern;
+				} else if (num_narrow > 0) {
+					// Some expolygons are narrow, split the fills.
+					params = fill.params;
+					params.pattern = narrow_pattern;
+					surface_fills.emplace_back(params);
+					SurfaceFill &old_fill = surface_fills[surface_fill_id];
+					SurfaceFill &new_fill = surface_fills.back();
+					new_fill.region_id 				= old_fill.region_id;
+					new_fill.surface.surface_type 	= stInternalSolid;
+					new_fill.surface.thickness 		= old_fill.surface.thickness;
+					new_fill.expolygons.reserve(num_narrow);
+					for (size_t i = 0; i < narrow_expolygons.size(); ++ i)
+						if (narrow_expolygons[i])
+							new_fill.expolygons.emplace_back(std::move(old_fill.expolygons[i]));
+					old_fill.expolygons.erase(std::remove_if(old_fill.expolygons.begin(), old_fill.expolygons.end(),
+						[&narrow_expolygons, ex_first = old_fill.expolygons.data()](const ExPolygon& ex) { return narrow_expolygons[&ex - ex_first]; }),
+						old_fill.expolygons.end());
+				}
+			}
+	}
+
 	return surface_fills;
 }
 
@@ -443,6 +486,14 @@ void Layer::make_fills(FillAdaptive::Octree* adaptive_fill_octree, FillAdaptive:
 
 	size_t first_object_layer_id = this->object()->get_layer(0)->id();
     for (SurfaceFill &surface_fill : surface_fills) {
+		//skip patterns for which additional input is nullptr
+		switch (surface_fill.params.pattern) {
+			case ipLightning: if (lightning_generator == nullptr) continue; break;
+			case ipAdaptiveCubic: if (adaptive_fill_octree == nullptr) continue; break;
+			case ipSupportCubic: if (support_fill_octree == nullptr) continue; break;
+			default: break;
+		}
+
         // Create the filler object.
         std::unique_ptr<Fill> f = std::unique_ptr<Fill>(Fill::new_from_type(surface_fill.params.pattern));
         f->set_bounding_box(bbox);
@@ -452,7 +503,9 @@ void Layer::make_fills(FillAdaptive::Octree* adaptive_fill_octree, FillAdaptive:
         f->layer_id = this->id() - first_object_layer_id;
         f->z 		= this->print_z;
         f->angle 	= surface_fill.params.angle;
-        f->adapt_fill_octree = (surface_fill.params.pattern == ipSupportCubic) ? support_fill_octree : adaptive_fill_octree;
+        f->adapt_fill_octree   = (surface_fill.params.pattern == ipSupportCubic) ? support_fill_octree : adaptive_fill_octree;
+        f->print_config        = &this->object()->print()->config();
+        f->print_object_config = &this->object()->config();
 
 		if (surface_fill.params.pattern == ipLightning) {
 			auto *lf = dynamic_cast<FillLightning::Filler*>(f.get());
@@ -460,11 +513,10 @@ void Layer::make_fills(FillAdaptive::Octree* adaptive_fill_octree, FillAdaptive:
 			lf->num_raft_layers = this->object()->slicing_parameters().raft_layers();
 		}
 
-        if (perimeter_generator.value == PerimeterGeneratorType::Arachne && surface_fill.params.pattern == ipConcentric) {
+        if (surface_fill.params.pattern == ipEnsuring) {
-            FillConcentric *fill_concentric = dynamic_cast<FillConcentric *>(f.get());
+            auto *fill_bounded_rectilinear = dynamic_cast<FillEnsuring *>(f.get());
-            assert(fill_concentric != nullptr);
+            assert(fill_bounded_rectilinear != nullptr);
-            fill_concentric->print_config        = &this->object()->print()->config();
+            fill_bounded_rectilinear->print_region_config = &m_regions[surface_fill.region_id]->region().config();
-            fill_concentric->print_object_config = &this->object()->config();
         }
 
         // calculate flow spacing for infill pattern generation
@@ -494,7 +546,7 @@ void Layer::make_fills(FillAdaptive::Octree* adaptive_fill_octree, FillAdaptive:
         params.anchor_length     = surface_fill.params.anchor_length;
         params.anchor_length_max = surface_fill.params.anchor_length_max;
         params.resolution        = resolution;
-        params.use_arachne       = perimeter_generator == PerimeterGeneratorType::Arachne && surface_fill.params.pattern == ipConcentric;
+        params.use_arachne       = (perimeter_generator == PerimeterGeneratorType::Arachne && surface_fill.params.pattern == ipConcentric) || surface_fill.params.pattern == ipEnsuring;
         params.layer_height      = layerm.layer()->height;
 
         for (ExPolygon &expoly : surface_fill.expolygons) {
@@ -595,6 +647,94 @@ void Layer::make_fills(FillAdaptive::Octree* adaptive_fill_octree, FillAdaptive:
 #endif
 }
 
+Polylines Layer::generate_sparse_infill_polylines_for_anchoring() const
+{
+    std::vector<SurfaceFill>  surface_fills = group_fills(*this);
+    const Slic3r::BoundingBox bbox          = this->object()->bounding_box();
+    const auto                resolution    = this->object()->print()->config().gcode_resolution.value;
+
+    Polylines sparse_infill_polylines{};
+
+    for (SurfaceFill &surface_fill : surface_fills) {
+        // skip patterns for which additional input is nullptr
+        switch (surface_fill.params.pattern) {
+        case ipLightning: continue; break;
+        case ipAdaptiveCubic: continue; break;
+        case ipSupportCubic: continue; break;
+        case ipCount: continue; break;
+        case ipSupportBase: continue; break;
+        case ipEnsuring: continue; break;
+        case ipRectilinear:
+        case ipMonotonic:
+        case ipMonotonicLines:
+        case ipAlignedRectilinear:
+        case ipGrid:
+        case ipTriangles:
+        case ipStars:
+        case ipCubic:
+        case ipLine:
+        case ipConcentric:
+        case ipHoneycomb:
+        case ip3DHoneycomb:
+        case ipGyroid:
+        case ipHilbertCurve:
+        case ipArchimedeanChords:
+        case ipOctagramSpiral: break;
+        }
+
+        // Create the filler object.
+        std::unique_ptr<Fill> f = std::unique_ptr<Fill>(Fill::new_from_type(surface_fill.params.pattern));
+        f->set_bounding_box(bbox);
+        f->layer_id = this->id();
+        f->z        = this->print_z;
+        f->angle    = surface_fill.params.angle;
+        // f->adapt_fill_octree   = (surface_fill.params.pattern == ipSupportCubic) ? support_fill_octree : adaptive_fill_octree;
+        f->print_config        = &this->object()->print()->config();
+        f->print_object_config = &this->object()->config();
+
+        // calculate flow spacing for infill pattern generation
+        double link_max_length = 0.;
+        if (!surface_fill.params.bridge) {
+#if 0
+            link_max_length = layerm.region()->config().get_abs_value(surface.is_external() ? "external_fill_link_max_length" : "fill_link_max_length", flow.spacing());
+//            printf("flow spacing: %f,  is_external: %d, link_max_length: %lf\n", flow.spacing(), int(surface.is_external()), link_max_length);
+#else
+            if (surface_fill.params.density > 80.) // 80%
+                link_max_length = 3. * f->spacing;
+#endif
+        }
+
+        // Maximum length of the perimeter segment linking two infill lines.
+        f->link_max_length = (coord_t) scale_(link_max_length);
+        // Used by the concentric infill pattern to clip the loops to create extrusion paths.
+        f->loop_clipping = coord_t(scale_(surface_fill.params.flow.nozzle_diameter()) * LOOP_CLIPPING_LENGTH_OVER_NOZZLE_DIAMETER);
+
+        LayerRegion &layerm = *m_regions[surface_fill.region_id];
+
+        // apply half spacing using this flow's own spacing and generate infill
+        FillParams params;
+        params.density           = float(0.01 * surface_fill.params.density);
+        params.dont_adjust       = false; //  surface_fill.params.dont_adjust;
+        params.anchor_length     = surface_fill.params.anchor_length;
+        params.anchor_length_max = surface_fill.params.anchor_length_max;
+        params.resolution        = resolution;
+        params.use_arachne       = false;
+        params.layer_height      = layerm.layer()->height;
+
+        for (ExPolygon &expoly : surface_fill.expolygons) {
+            // Spacing is modified by the filler to indicate adjustments. Reset it for each expolygon.
+            f->spacing                     = surface_fill.params.spacing;
+            surface_fill.surface.expolygon = std::move(expoly);
+            try {
+                Polylines polylines = f->fill_surface(&surface_fill.surface, params);
+                sparse_infill_polylines.insert(sparse_infill_polylines.end(), polylines.begin(), polylines.end());
+            } catch (InfillFailedException &) {}
+        }
+    }
+
+    return sparse_infill_polylines;
+}
+
 // Create ironing extrusions over top surfaces.
 void Layer::make_ironing()
 {

src/libslic3r/Fill/FillBase.cpp

@@ -20,6 +20,7 @@
 #include "FillRectilinear.hpp"
 #include "FillAdaptive.hpp"
 #include "FillLightning.hpp"
+#include "FillEnsuring.hpp"
 
 #include <boost/log/trivial.hpp>
 
@@ -50,6 +51,7 @@ Fill* Fill::new_from_type(const InfillPattern type)
     case ipSupportCubic:        return new FillAdaptive::Filler();
     case ipSupportBase:         return new FillSupportBase();
     case ipLightning:           return new FillLightning::Filler();
+    case ipEnsuring:            return new FillEnsuring();
     default: throw Slic3r::InvalidArgument("unknown type");
     }
 }

src/libslic3r/Fill/FillBase.hpp

@@ -91,6 +91,10 @@ public:
     // Octree builds on mesh for usage in the adaptive cubic infill
     FillAdaptive::Octree* adapt_fill_octree = nullptr;
 
+    // PrintConfig and PrintObjectConfig are used by infills that use Arachne (Concentric and FillEnsuring).
+    const PrintConfig       *print_config        = nullptr;
+    const PrintObjectConfig *print_object_config = nullptr;
+
 public:
     virtual ~Fill() {}
     virtual Fill* clone() const = 0;

src/libslic3r/Fill/FillConcentric.cpp

@@ -97,14 +97,8 @@ void FillConcentric::_fill_surface_single(const FillParams              &params,
                 continue;
 
             ThickPolyline thick_polyline = Arachne::to_thick_polyline(*extrusion);
-            if (extrusion->is_closed && thick_polyline.points.front() == thick_polyline.points.back() && thick_polyline.width.front() == thick_polyline.width.back()) {
+            if (extrusion->is_closed)
-                thick_polyline.points.pop_back();
+                thick_polyline.start_at_index(nearest_point_index(thick_polyline.points, last_pos));
-                assert(thick_polyline.points.size() * 2 == thick_polyline.width.size());
-                int nearest_idx = nearest_point_index(thick_polyline.points, last_pos);
-                std::rotate(thick_polyline.points.begin(), thick_polyline.points.begin() + nearest_idx, thick_polyline.points.end());
-                std::rotate(thick_polyline.width.begin(), thick_polyline.width.begin() + 2 * nearest_idx, thick_polyline.width.end());
-                thick_polyline.points.emplace_back(thick_polyline.points.front());
-            }
             thick_polylines_out.emplace_back(std::move(thick_polyline));
             last_pos = thick_polylines_out.back().last_point();
         }

src/libslic3r/Fill/FillConcentric.hpp

@@ -26,11 +26,6 @@ protected:
                               ThickPolylines                &thick_polylines_out) override;
 
     bool no_sort() const override { return true; }
-
-    const PrintConfig       *print_config        = nullptr;
-    const PrintObjectConfig *print_object_config = nullptr;
-
-    friend class Layer;
 };
 
 } // namespace Slic3r

src/libslic3r/Fill/FillEnsuring.cpp

@@ -0,0 +1,83 @@
+#include "../ClipperUtils.hpp"
+#include "../ShortestPath.hpp"
+#include "../Arachne/WallToolPaths.hpp"
+
+#include "FillEnsuring.hpp"
+
+#include <boost/log/trivial.hpp>
+
+namespace Slic3r {
+
+ThickPolylines FillEnsuring::fill_surface_arachne(const Surface *surface, const FillParams &params)
+{
+    assert(params.use_arachne);
+    assert(this->print_config != nullptr && this->print_object_config != nullptr && this->print_region_config != nullptr);
+
+    const coord_t               scaled_spacing         = scaled<coord_t>(this->spacing);
+
+    // Perform offset.
+    Slic3r::ExPolygons expp = this->overlap != 0. ? offset_ex(surface->expolygon, scaled<float>(this->overlap)) : ExPolygons{surface->expolygon};
+    // Create the infills for each of the regions.
+    ThickPolylines thick_polylines_out;
+    for (ExPolygon &ex_poly : expp) {
+        Point    bbox_size   = ex_poly.contour.bounding_box().size();
+        coord_t  loops_count = std::max(bbox_size.x(), bbox_size.y()) / scaled_spacing + 1;
+        Polygons polygons    = to_polygons(ex_poly);
+        Arachne::WallToolPaths wall_tool_paths(polygons, scaled_spacing, scaled_spacing, loops_count, 0, params.layer_height, *this->print_object_config, *this->print_config);
+        if (std::vector<Arachne::VariableWidthLines> loops = wall_tool_paths.getToolPaths(); !loops.empty()) {
+            assert(!is_bounded_rectilinear || loops.size() == 1);
+            std::vector<const Arachne::ExtrusionLine *> all_extrusions;
+            for (Arachne::VariableWidthLines &loop : loops) {
+                if (loop.empty())
+                    continue;
+                for (const Arachne::ExtrusionLine &wall : loop)
+                    all_extrusions.emplace_back(&wall);
+            }
+
+            // Split paths using a nearest neighbor search.
+            size_t firts_poly_idx = thick_polylines_out.size();
+            Point  last_pos(0, 0);
+            for (const Arachne::ExtrusionLine *extrusion : all_extrusions) {
+                if (extrusion->empty())
+                    continue;
+
+                ThickPolyline thick_polyline = Arachne::to_thick_polyline(*extrusion);
+                if (thick_polyline.length() == 0.)
+                    //FIXME this should not happen.
+                    continue;
+                assert(thick_polyline.size() > 1);
+                assert(thick_polyline.length() > 0.);
+                //assert(thick_polyline.points.size() == thick_polyline.width.size());
+                if (extrusion->is_closed)
+                    thick_polyline.start_at_index(nearest_point_index(thick_polyline.points, last_pos));
+
+                assert(thick_polyline.size() > 1);
+                //assert(thick_polyline.points.size() == thick_polyline.width.size());
+                thick_polylines_out.emplace_back(std::move(thick_polyline));
+                last_pos = thick_polylines_out.back().last_point();
+            }
+
+            // clip the paths to prevent the extruder from getting exactly on the first point of the loop
+            // Keep valid paths only.
+            size_t j = firts_poly_idx;
+            for (size_t i = firts_poly_idx; i < thick_polylines_out.size(); ++i) {
+                assert(thick_polylines_out[i].size() > 1);
+                assert(thick_polylines_out[i].length() > 0.);
+                //assert(thick_polylines_out[i].points.size() == thick_polylines_out[i].width.size());
+                thick_polylines_out[i].clip_end(this->loop_clipping);
+                assert(thick_polylines_out[i].size() > 1);
+                if (thick_polylines_out[i].is_valid()) {
+                    if (j < i)
+                        thick_polylines_out[j] = std::move(thick_polylines_out[i]);
+                    ++j;
+                }
+            }
+            if (j < thick_polylines_out.size())
+                thick_polylines_out.erase(thick_polylines_out.begin() + int(j), thick_polylines_out.end());
+        }
+    }
+
+    return thick_polylines_out;
+}
+
+} // namespace Slic3r

src/libslic3r/Fill/FillEnsuring.hpp

@@ -0,0 +1,30 @@
+#ifndef slic3r_FillEnsuring_hpp_
+#define slic3r_FillEnsuring_hpp_
+
+#include "FillBase.hpp"
+#include "FillRectilinear.hpp"
+
+namespace Slic3r {
+
+class FillEnsuring : public FillRectilinear
+{
+public:
+    Fill *clone() const override { return new FillEnsuring(*this); }
+    ~FillEnsuring() override = default;
+    Polylines      fill_surface(const Surface *surface, const FillParams &params) override { return {}; };
+    ThickPolylines fill_surface_arachne(const Surface *surface, const FillParams &params) override;
+
+protected:
+    void fill_surface_single_arachne(const Surface &surface, const FillParams &params, ThickPolylines &thick_polylines_out);
+
+    bool no_sort() const override { return true; }
+
+    // PrintRegionConfig is used for computing overlap between boundary contour and inner Rectilinear infill.
+    const PrintRegionConfig *print_region_config = nullptr;
+
+    friend class Layer;
+};
+
+} // namespace Slic3r
+
+#endif // slic3r_FillEnsuring_hpp_

src/libslic3r/Fill/FillRectilinear.hpp

@@ -7,6 +7,7 @@
 
 namespace Slic3r {
 
+class PrintRegionConfig;
 class Surface;
 
 class FillRectilinear : public Fill

src/libslic3r/GCode/CoolingBuffer.cpp

@@ -378,7 +378,8 @@ std::vector<PerExtruderAdjustments> CoolingBuffer::parse_layer_gcode(const std::
                 size_t axis = (*c >= 'X' && *c <= 'Z') ? (*c - 'X') :
                               (*c == extrusion_axis) ? 3 : (*c == 'F') ? 4 : size_t(-1);
                 if (axis != size_t(-1)) {
-                    auto [pend, ec] = fast_float::from_chars(&*(++ c), sline.data() + sline.size(), new_pos[axis]);
+                    //auto [pend, ec] = 
+                        fast_float::from_chars(&*(++ c), sline.data() + sline.size(), new_pos[axis]);
                     if (axis == 4) {
                         // Convert mm/min to mm/sec.
                         new_pos[4] /= 60.f;
@@ -497,7 +498,8 @@ std::vector<PerExtruderAdjustments> CoolingBuffer::parse_layer_gcode(const std::
             bool   has_S = pos_S > 0;
             bool   has_P = pos_P > 0;
             if (has_S || has_P) {
-                auto [pend, ec] = fast_float::from_chars(sline.data() + (has_S ? pos_S : pos_P) + 1, sline.data() + sline.size(), line.time);
+                //auto [pend, ec] = 
+                    fast_float::from_chars(sline.data() + (has_S ? pos_S : pos_P) + 1, sline.data() + sline.size(), line.time);
                 if (has_P)
                     line.time *= 0.001f;
             } else
@@ -846,7 +848,8 @@ std::string CoolingBuffer::apply_layer_cooldown(
             if (line->slowdown)
                 new_feedrate = int(floor(60. * line->feedrate + 0.5));
             else
-                auto res = std::from_chars(fpos, line_end, new_feedrate);
+                //auto res = 
+                    std::from_chars(fpos, line_end, new_feedrate);
             if (new_feedrate == current_feedrate) {
                 // No need to change the F value.
                 if ((line->type & (CoolingLine::TYPE_ADJUSTABLE | CoolingLine::TYPE_ADJUSTABLE_EMPTY | CoolingLine::TYPE_EXTERNAL_PERIMETER | CoolingLine::TYPE_WIPE)) || line->length == 0.)

src/libslic3r/GCode/RetractWhenCrossingPerimeters.cpp

@@ -19,20 +19,7 @@ bool RetractWhenCrossingPerimeters::travel_inside_internal_regions(const Layer &
                 if (surface.is_internal())
                     m_internal_islands.emplace_back(&surface.expolygon);
         // Calculate bounding boxes of internal slices.
-        class BBoxWrapper {
+        std::vector<AABBTreeIndirect::BoundingBoxWrapper> bboxes;
-        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]));

src/libslic3r/Geometry/MedialAxis.cpp

@@ -468,9 +468,6 @@ void MedialAxis::build(ThickPolylines* polylines)
     }
     */
     
-    //typedef const VD::vertex_type vert_t;
-    using edge_t = const VD::edge_type;
-    
     // collect valid edges (i.e. prune those not belonging to MAT)
     // note: this keeps twins, so it inserts twice the number of the valid edges
     m_edge_data.assign(m_vd.edges().size() / 2, EdgeData{});

src/libslic3r/Layer.cpp

@@ -1,5 +1,5 @@
 #include "Layer.hpp"
-#include <clipper/clipper_z.hpp>
+#include "ClipperZUtils.hpp"
 #include "ClipperUtils.hpp"
 #include "Print.hpp"
 #include "Fill/Fill.hpp"
@@ -302,48 +302,16 @@ void Layer::build_up_down_graph(Layer& below, Layer& above)
     coord_t             paths_end = paths_above_offset + coord_t(above.lslices.size());
 #endif // NDEBUG
 
-    class ZFill {
-    public:
-        ZFill() = default;
-        void reset() { m_intersections.clear(); }
-        void operator()(
-            const ClipperLib_Z::IntPoint& e1bot, const ClipperLib_Z::IntPoint& e1top,
-            const ClipperLib_Z::IntPoint& e2bot, const ClipperLib_Z::IntPoint& e2top,
-            ClipperLib_Z::IntPoint& pt) {
-            coord_t srcs[4]{ e1bot.z(), e1top.z(), e2bot.z(), e2top.z() };
-            coord_t* begin = srcs;
-            coord_t* end = srcs + 4;
-            std::sort(begin, end);
-            end = std::unique(begin, end);
-            if (begin + 1 == end) {
-                // Self intersection may happen on source contour. Just copy the Z value.
-                pt.z() = *begin;
-            } else {
-                assert(begin + 2 == end);
-                if (begin + 2 <= end) {
-                    // store a -1 based negative index into the "intersections" vector here.
-                    m_intersections.emplace_back(srcs[0], srcs[1]);
-                    pt.z() = -coord_t(m_intersections.size());
-                }
-            }
-        }
-        const std::vector<std::pair<coord_t, coord_t>>& intersections() const { return m_intersections; }
-
-    private:
-        std::vector<std::pair<coord_t, coord_t>> m_intersections;
-    } zfill;
-
     ClipperLib_Z::Clipper  clipper;
     ClipperLib_Z::PolyTree result;
-    clipper.ZFillFunction(
+    ClipperZUtils::ClipperZIntersectionVisitor::Intersections intersections;
-        [&zfill](const ClipperLib_Z::IntPoint &e1bot, const ClipperLib_Z::IntPoint &e1top, 
+    ClipperZUtils::ClipperZIntersectionVisitor visitor(intersections);
-                 const ClipperLib_Z::IntPoint &e2bot, const ClipperLib_Z::IntPoint &e2top, ClipperLib_Z::IntPoint &pt)
+    clipper.ZFillFunction(visitor.clipper_callback());
-        { return zfill(e1bot, e1top, e2bot, e2top, pt); });
     clipper.AddPaths(paths_below, ClipperLib_Z::ptSubject, true);
     clipper.AddPaths(paths_above, ClipperLib_Z::ptClip, true);
     clipper.Execute(ClipperLib_Z::ctIntersection, result, ClipperLib_Z::pftNonZero, ClipperLib_Z::pftNonZero);
 
-    connect_layer_slices(below, above, result, zfill.intersections(), paths_below_offset, paths_above_offset
+    connect_layer_slices(below, above, result, intersections, paths_below_offset, paths_above_offset
 #ifndef NDEBUG
         , paths_end
 #endif // NDEBUG

src/libslic3r/Layer.hpp

@@ -134,7 +134,7 @@ public:
     
     Flow    flow(FlowRole role) const;
     Flow    flow(FlowRole role, double layer_height) const;
-    Flow    bridging_flow(FlowRole role) const;
+    Flow    bridging_flow(FlowRole role, bool force_thick_bridges = false) const;
 
     void    slices_to_fill_surfaces_clipped();
     void    prepare_fill_surfaces();
@@ -369,6 +369,7 @@ public:
     // Phony version of make_fills() without parameters for Perl integration only.
     void                    make_fills() { this->make_fills(nullptr, nullptr, nullptr); }
     void                    make_fills(FillAdaptive::Octree* adaptive_fill_octree, FillAdaptive::Octree* support_fill_octree, FillLightning::Generator* lightning_generator);
+    Polylines               generate_sparse_infill_polylines_for_anchoring() const;
     void 					make_ironing();
 
     void                    export_region_slices_to_svg(const char *path) const;

src/libslic3r/LayerRegion.cpp

@@ -8,6 +8,7 @@
 #include "Surface.hpp"
 #include "BoundingBox.hpp"
 #include "SVG.hpp"
+#include "Algorithm/RegionExpansion.hpp"
 
 #include <string>
 #include <map>
@@ -26,12 +27,12 @@ Flow LayerRegion::flow(FlowRole role, double layer_height) const
     return m_region->flow(*m_layer->object(), role, layer_height, m_layer->id() == 0);
 }
 
-Flow LayerRegion::bridging_flow(FlowRole role) const
+Flow LayerRegion::bridging_flow(FlowRole role, bool force_thick_bridges) const
 {
     const PrintRegion       &region         = this->region();
     const PrintRegionConfig &region_config  = region.config();
     const PrintObject       &print_object   = *this->layer()->object();
-    if (print_object.config().thick_bridges) {
+    if (print_object.config().thick_bridges || force_thick_bridges) {
         // The old Slic3r way (different from all other slicers): Use rounded extrusions.
         // Get the configured nozzle_diameter for the extruder associated to the flow role requested.
         // Here this->extruder(role) - 1 may underflow to MAX_INT, but then the get_at() will follback to zero'th element, so everything is all right.
@@ -139,6 +140,273 @@ void LayerRegion::make_perimeters(
     }
 }
 
+#if 1
+
+// Extract surfaces of given type from surfaces, extract fill (layer) thickness of one of the surfaces.
+static ExPolygons fill_surfaces_extract_expolygons(Surfaces &surfaces, SurfaceType surface_type, double &thickness)
+{
+    size_t cnt = 0;
+    for (const Surface &surface : surfaces)
+        if (surface.surface_type == surface_type) {
+            ++ cnt;
+            thickness = surface.thickness;
+        }
+    if (cnt == 0)
+        return {};
+
+    ExPolygons out;
+    out.reserve(cnt);
+    for (Surface &surface : surfaces)
+        if (surface.surface_type == surface_type)
+            out.emplace_back(std::move(surface.expolygon));
+    return out;
+}
+
+// Extract bridging surfaces from "surfaces", expand them into "shells" using expansion_params,
+// detect bridges.
+// Trim "shells" by the expanded bridges.
+Surfaces expand_bridges_detect_orientations(
+    Surfaces                                    &surfaces,
+    ExPolygons                                  &shells,
+    const Algorithm::RegionExpansionParameters  &expansion_params)
+{
+    using namespace Slic3r::Algorithm;
+
+    double thickness;
+    ExPolygons bridges_ex = fill_surfaces_extract_expolygons(surfaces, stBottomBridge, thickness);
+    if (bridges_ex.empty())
+        return {};
+
+    // Calculate bridge anchors and their expansions in their respective shell region.
+    WaveSeeds                       bridge_anchors    = wave_seeds(bridges_ex, shells, expansion_params.tiny_expansion, true);
+    std::vector<RegionExpansionEx>  bridge_expansions = propagate_waves_ex(bridge_anchors, shells, expansion_params);
+
+    // Cache for detecting bridge orientation and merging regions with overlapping expansions.
+    struct Bridge {
+        ExPolygon                                       expolygon;
+        uint32_t                                        group_id;
+        std::vector<RegionExpansionEx>::const_iterator  bridge_expansion_begin;
+        double                                          angle = -1;
+    };
+    std::vector<Bridge> bridges;
+    {
+        bridges.reserve(bridges_ex.size());
+        uint32_t group_id = 0;
+        for (ExPolygon &ex : bridges_ex)
+            bridges.push_back({ std::move(ex), group_id ++, bridge_expansions.end() });
+        bridges_ex.clear();
+    }
+
+    // Group the bridge surfaces by overlaps.
+    auto group_id = [&bridges](uint32_t src_id) {
+        uint32_t group_id = bridges[src_id].group_id;
+        while (group_id != src_id) {
+            src_id = group_id;
+            group_id = bridges[src_id].group_id;
+        }
+        bridges[src_id].group_id = group_id;
+        return group_id;
+    };
+
+    {
+        // Cache of bboxes per expansion boundary.
+        std::vector<BoundingBox> bboxes;
+        // Detect overlaps of bridge anchors inside their respective shell regions.
+        // bridge_expansions are sorted by boundary id and source id.
+        for (auto it = bridge_expansions.begin(); it != bridge_expansions.end();) {
+            // For each boundary region:
+            auto it_begin = it;
+            auto it_end   = std::next(it_begin);
+            for (; it_end != bridge_expansions.end() && it_end->boundary_id == it_begin->boundary_id; ++ it_end) ;
+            bboxes.clear();
+            bboxes.reserve(it_end - it_begin);
+            for (auto it2 = it_begin; it2 != it_end; ++ it2)
+                bboxes.emplace_back(get_extents(it2->expolygon.contour));
+            // For each bridge anchor of the current source:
+            for (; it != it_end; ++ it) {
+                // A grup id for this bridge.
+                for (auto it2 = std::next(it); it2 != it_end; ++ it2)
+                    if (it->src_id != it2->src_id &&
+                        bboxes[it - it_begin].overlap(bboxes[it2 - it_begin]) &&
+                        // One may ignore holes, they are irrelevant for intersection test.
+                        ! intersection(it->expolygon.contour, it2->expolygon.contour).empty()) {
+                        // The two bridge regions intersect. Give them the same group id.
+                        uint32_t id  = group_id(it->src_id);
+                        uint32_t id2 = group_id(it2->src_id);
+                        bridges[it->src_id].group_id = bridges[it2->src_id].group_id = std::min(id, id2);
+                    }
+            }
+        }
+    }
+
+    // Detect bridge directions.
+    {
+        std::sort(bridge_anchors.begin(), bridge_anchors.end(), Algorithm::lower_by_src_and_boundary);
+        auto it_bridge_anchor = bridge_anchors.begin();
+        Lines lines;
+        Polygons anchor_areas;
+        for (uint32_t bridge_id = 0; bridge_id < uint32_t(bridges.size()); ++ bridge_id) {
+            Bridge &bridge = bridges[bridge_id];
+//            lines.clear();
+            anchor_areas.clear();
+            int32_t last_anchor_id = -1;
+            for (; it_bridge_anchor != bridge_anchors.end() && it_bridge_anchor->src == bridge_id; ++ it_bridge_anchor) {
+                if (last_anchor_id != int(it_bridge_anchor->boundary)) {
+                    last_anchor_id = int(it_bridge_anchor->boundary);
+                    append(anchor_areas, to_polygons(shells[last_anchor_id]));
+                }
+//                if (Points &polyline = it_bridge_anchor->path; polyline.size() >= 2) {
+//                    reserve_more_power_of_2(lines, polyline.size() - 1);
+//                    for (size_t i = 1; i < polyline.size(); ++ i)
+//                        lines.push_back({ polyline[i - 1], polyline[1] });
+//                }
+            }
+            lines = to_lines(diff_pl(to_polylines(bridge.expolygon), expand(anchor_areas, float(SCALED_EPSILON))));
+            auto [bridging_dir, unsupported_dist] = detect_bridging_direction(lines, to_polygons(bridge.expolygon));
+            bridge.angle = M_PI + std::atan2(bridging_dir.y(), bridging_dir.x());
+            // #if 1
+            //     coordf_t    stroke_width = scale_(0.06);
+            //     BoundingBox bbox         = get_extents(initial);
+            //     bbox.offset(scale_(1.));
+            //     ::Slic3r::SVG
+            //     svg(debug_out_path(("bridge"+std::to_string(bridges[idx_last].bridge_angle)+"_"+std::to_string(this->layer()->bottom_z())).c_str()),
+            //     bbox);
+
+            //     svg.draw(initial, "cyan");
+            //     svg.draw(to_lines(lower_layer->lslices), "green", stroke_width);
+            // #endif
+        }
+    }
+
+    // Merge the groups with the same group id, produce surfaces by merging source overhangs with their newly expanded anchors.
+    Surfaces out;
+    {
+        Polygons acc;
+        Surface templ{ stBottomBridge, {} };
+        std::sort(bridge_expansions.begin(), bridge_expansions.end(), [](auto &l, auto &r) {
+            return l.src_id < r.src_id || (l.src_id == r.src_id && l.boundary_id < r.boundary_id);
+        });
+        for (auto it = bridge_expansions.begin(); it != bridge_expansions.end(); ) {
+            bridges[it->src_id].bridge_expansion_begin = it;
+            uint32_t src_id = it->src_id;
+            for (++ it; it != bridge_expansions.end() && it->src_id == src_id; ++ it) ;
+        }
+        for (uint32_t bridge_id = 0; bridge_id < uint32_t(bridges.size()); ++ bridge_id) {
+            acc.clear();
+            for (uint32_t bridge_id2 = bridge_id; bridge_id2 < uint32_t(bridges.size()); ++ bridge_id2)
+                if (group_id(bridge_id) == bridge_id) {
+                    append(acc, to_polygons(std::move(bridges[bridge_id2].expolygon)));
+                    auto it_bridge_expansion = bridges[bridge_id2].bridge_expansion_begin;
+                    assert(it_bridge_expansion == bridge_expansions.end() || it_bridge_expansion->src_id == bridge_id2);
+                    for (; it_bridge_expansion != bridge_expansions.end() && it_bridge_expansion->src_id == bridge_id2; ++ it_bridge_expansion)
+                        append(acc, to_polygons(std::move(it_bridge_expansion->expolygon)));
+                }
+            //FIXME try to be smart and pick the best bridging angle for all?
+            templ.bridge_angle = bridges[bridge_id].angle;
+            // without safety offset, artifacts are generated (GH #2494)
+            for (ExPolygon &ex : union_safety_offset_ex(acc))
+                out.emplace_back(templ, std::move(ex));
+        }
+    }
+
+    // Clip the shells by the expanded bridges.
+    shells = diff_ex(shells, out);
+    return out;
+}
+
+// Extract bridging surfaces from "surfaces", expand them into "shells" using expansion_params.
+// Trim "shells" by the expanded bridges.
+static Surfaces expand_merge_surfaces(
+    Surfaces                                   &surfaces,
+    SurfaceType                                 surface_type,
+    ExPolygons                                 &shells,
+    const Algorithm::RegionExpansionParameters &params,
+    const double                                bridge_angle = -1.)
+{
+    double thickness;
+    ExPolygons src = fill_surfaces_extract_expolygons(surfaces, surface_type, thickness);
+    if (src.empty())
+        return {};
+
+    std::vector<ExPolygon> expanded = expand_merge_expolygons(std::move(src), shells, params);
+    // Trim the shells by the expanded expolygons.
+    shells = diff_ex(shells, expanded);
+
+    Surface templ{ surface_type, {} };
+    templ.bridge_angle = bridge_angle;
+    Surfaces out;
+    out.reserve(expanded.size());
+    for (auto &expoly : expanded)
+        out.emplace_back(templ, std::move(expoly));
+    return out;
+}
+
+void LayerRegion::process_external_surfaces(const Layer *lower_layer, const Polygons *lower_layer_covered)
+{
+#ifdef SLIC3R_DEBUG_SLICE_PROCESSING
+    export_region_fill_surfaces_to_svg_debug("4_process_external_surfaces-initial");
+#endif /* SLIC3R_DEBUG_SLICE_PROCESSING */
+
+    // Width of the perimeters.
+    float shell_width = 0;
+    if (int num_perimeters = this->region().config().perimeters; num_perimeters > 0) {
+        Flow external_perimeter_flow = this->flow(frExternalPerimeter);
+        Flow perimeter_flow          = this->flow(frPerimeter);
+        shell_width += 0.5f * external_perimeter_flow.scaled_width() + external_perimeter_flow.scaled_spacing();
+        shell_width += perimeter_flow.scaled_spacing() * (num_perimeters - 1);
+    } else {
+    }
+
+    // Scaled expansions of the respective external surfaces.
+    float                           expansion_top           = shell_width * sqrt(2.);
+    float                           expansion_bottom        = expansion_top;
+    float                           expansion_bottom_bridge = expansion_top;
+    // Expand by waves of expansion_step size (expansion_step is scaled), but with no more steps than max_nr_expansion_steps.
+    static constexpr const float    expansion_step          = scaled<float>(0.1);
+    // Don't take more than max_nr_steps for small expansion_step.
+    static constexpr const size_t   max_nr_expansion_steps  = 5;
+
+    // Expand the top / bottom / bridge surfaces into the shell thickness solid infills.
+    double     layer_thickness;
+    ExPolygons shells = union_ex(fill_surfaces_extract_expolygons(m_fill_surfaces.surfaces, stInternalSolid, layer_thickness));
+
+    SurfaceCollection bridges;
+    {
+        BOOST_LOG_TRIVIAL(trace) << "Processing external surface, detecting bridges. layer" << this->layer()->print_z;
+        const double custom_angle = this->region().config().bridge_angle.value;
+        const auto   params = Algorithm::RegionExpansionParameters::build(expansion_bottom_bridge, expansion_step, max_nr_expansion_steps);
+        bridges.surfaces = custom_angle > 0 ?
+            expand_merge_surfaces(m_fill_surfaces.surfaces, stBottomBridge, shells, params, custom_angle) :
+            expand_bridges_detect_orientations(m_fill_surfaces.surfaces, shells, params);
+        BOOST_LOG_TRIVIAL(trace) << "Processing external surface, detecting bridges - done";
+#if 0
+        {
+            static int iRun = 0;
+            bridges.export_to_svg(debug_out_path("bridges-after-grouping-%d.svg", iRun++), true);
+        }
+#endif
+    }
+
+    Surfaces    bottoms = expand_merge_surfaces(m_fill_surfaces.surfaces, stBottom, shells,
+        Algorithm::RegionExpansionParameters::build(expansion_bottom, expansion_step, max_nr_expansion_steps));
+    Surfaces    tops    = expand_merge_surfaces(m_fill_surfaces.surfaces, stTop, shells,
+        Algorithm::RegionExpansionParameters::build(expansion_top, expansion_step, max_nr_expansion_steps));
+
+    m_fill_surfaces.remove_types({ stBottomBridge, stBottom, stTop, stInternalSolid });
+    reserve_more(m_fill_surfaces.surfaces, shells.size() + bridges.size() + bottoms.size() + tops.size());
+    Surface solid_templ(stInternalSolid, {});
+    solid_templ.thickness = layer_thickness;
+    m_fill_surfaces.append(std::move(shells), solid_templ);
+    m_fill_surfaces.append(std::move(bridges.surfaces));
+    m_fill_surfaces.append(std::move(bottoms));
+    m_fill_surfaces.append(std::move(tops));
+
+#ifdef SLIC3R_DEBUG_SLICE_PROCESSING
+    export_region_fill_surfaces_to_svg_debug("4_process_external_surfaces-final");
+#endif /* SLIC3R_DEBUG_SLICE_PROCESSING */
+}
+#else
+
 //#define EXTERNAL_SURFACES_OFFSET_PARAMETERS ClipperLib::jtMiter, 3.
 //#define EXTERNAL_SURFACES_OFFSET_PARAMETERS ClipperLib::jtMiter, 1.5
 #define EXTERNAL_SURFACES_OFFSET_PARAMETERS ClipperLib::jtSquare, 0.
@@ -146,10 +414,11 @@ void LayerRegion::make_perimeters(
 void LayerRegion::process_external_surfaces(const Layer *lower_layer, const Polygons *lower_layer_covered)
 {
     const bool      has_infill = this->region().config().fill_density.value > 0.;
-    const float		margin 	   = float(scale_(EXTERNAL_INFILL_MARGIN));
+//    const float		margin     = scaled<float>(0.1); // float(scale_(EXTERNAL_INFILL_MARGIN));
+    const float     margin     = float(scale_(EXTERNAL_INFILL_MARGIN));
 
 #ifdef SLIC3R_DEBUG_SLICE_PROCESSING
-    export_region_fill_surfaces_to_svg_debug("3_process_external_surfaces-initial");
+    export_region_fill_surfaces_to_svg_debug("4_process_external_surfaces-initial");
 #endif /* SLIC3R_DEBUG_SLICE_PROCESSING */
 
     // 1) Collect bottom and bridge surfaces, each of them grown by a fixed 3mm offset
@@ -164,7 +433,6 @@ void LayerRegion::process_external_surfaces(const Layer *lower_layer, const Poly
     Surfaces                    internal;
     // Areas, where an infill of various types (top, bottom, bottom bride, sparse, void) could be placed.
     Polygons                    fill_boundaries = to_polygons(this->fill_expolygons());
-    Polygons  					lower_layer_covered_tmp;
 
     // Collect top surfaces and internal surfaces.
     // Collect fill_boundaries: If we're slicing with no infill, we can't extend external surfaces over non-existent infill.
@@ -174,33 +442,42 @@ void LayerRegion::process_external_surfaces(const Layer *lower_layer, const Poly
         // Voids are sparse infills if infill rate is zero.
         Polygons voids;
         for (const Surface &surface : this->fill_surfaces()) {
-            if (surface.is_top()) {
+            assert(! surface.empty());
-                // Collect the top surfaces, inflate them and trim them by the bottom surfaces.
+            if (! surface.empty()) {
-                // This gives the priority to bottom surfaces.
+                if (surface.is_top()) {
-                surfaces_append(top, offset_ex(surface.expolygon, margin, EXTERNAL_SURFACES_OFFSET_PARAMETERS), surface);
+                    // Collect the top surfaces, inflate them and trim them by the bottom surfaces.
-            } else if (surface.surface_type == stBottom || (surface.surface_type == stBottomBridge && lower_layer == nullptr)) {
+                    // This gives the priority to bottom surfaces.
-                // Grown by 3mm.
+                    surfaces_append(top, offset_ex(surface.expolygon, margin, EXTERNAL_SURFACES_OFFSET_PARAMETERS), surface);
-                surfaces_append(bottom, offset_ex(surface.expolygon, margin, EXTERNAL_SURFACES_OFFSET_PARAMETERS), surface);
+                } else if (surface.surface_type == stBottom || (surface.surface_type == stBottomBridge && lower_layer == nullptr)) {
-            } else if (surface.surface_type == stBottomBridge) {
+                    // Grown by 3mm.
-                if (! surface.empty())
+                    surfaces_append(bottom, offset_ex(surface.expolygon, margin, EXTERNAL_SURFACES_OFFSET_PARAMETERS), surface);
+                } else if (surface.surface_type == stBottomBridge) {
                     bridges.emplace_back(surface);
-            }
+                } else {
-            if (surface.is_internal()) {
+                    assert(surface.is_internal());
-            	assert(surface.surface_type == stInternal || surface.surface_type == stInternalSolid);
+                	assert(surface.surface_type == stInternal || surface.surface_type == stInternalSolid);
-            	if (! has_infill && lower_layer != nullptr)
+                	if (! has_infill && lower_layer != nullptr)
-            		polygons_append(voids, surface.expolygon);
+                		polygons_append(voids, surface.expolygon);
-            	internal.emplace_back(std::move(surface));
+                	internal.emplace_back(std::move(surface));
+                }
             }
         }
-        if (! has_infill && lower_layer != nullptr && ! voids.empty()) {
+        if (! voids.empty()) {
+            // There are some voids (empty infill regions) on this layer. Usually one does not want to expand
+            // any infill into these voids, with the exception the expanded infills are supported by layers below
+            // with nonzero inill.
+            assert(! has_infill && lower_layer != nullptr);
         	// Remove voids from fill_boundaries, that are not supported by the layer below.
+            Polygons lower_layer_covered_tmp;
             if (lower_layer_covered == nullptr) {
             	lower_layer_covered = &lower_layer_covered_tmp;
             	lower_layer_covered_tmp = to_polygons(lower_layer->lslices);
             }
             if (! lower_layer_covered->empty())
+                // Allow the top / bottom surfaces to expand into the voids of this layer if supported by the layer below.
             	voids = diff(voids, *lower_layer_covered);
-            fill_boundaries = diff(fill_boundaries, voids);
+            if (! voids.empty())
+                fill_boundaries = diff(fill_boundaries, voids);
         }
     }
 
@@ -224,13 +501,12 @@ void LayerRegion::process_external_surfaces(const Layer *lower_layer, const Poly
 #ifdef SLIC3R_DEBUG_SLICE_PROCESSING
         {
             static int iRun = 0;
-            SVG svg(debug_out_path("3_process_external_surfaces-fill_regions-%d.svg", iRun ++).c_str(), get_extents(fill_boundaries_ex));
+            SVG svg(debug_out_path("4_process_external_surfaces-fill_regions-%d.svg", iRun ++).c_str(), get_extents(fill_boundaries_ex));
             svg.draw(fill_boundaries_ex);
             svg.draw_outline(fill_boundaries_ex, "black", "blue", scale_(0.05)); 
             svg.Close();
         }
-
+//        export_region_fill_surfaces_to_svg_debug("4_process_external_surfaces-initial");
-//        export_region_fill_surfaces_to_svg_debug("3_process_external_surfaces-initial");
 #endif /* SLIC3R_DEBUG_SLICE_PROCESSING */
  
         {
@@ -253,7 +529,8 @@ void LayerRegion::process_external_surfaces(const Layer *lower_layer, const Poly
                 if (idx_island == -1) {
 				    BOOST_LOG_TRIVIAL(trace) << "Bridge did not fall into the source region!";
                 } else {
-                    // Found an island, to which this bridge region belongs. Trim it,
+                    // Found an island, to which this bridge region belongs. Trim the expanded bridging region
+                    // with its source region, so it does not overflow into a neighbor region.
                     polys = intersection(polys, fill_boundaries_ex[idx_island]);
                 }
                 bridge_bboxes.push_back(get_extents(polys));
@@ -371,10 +648,10 @@ void LayerRegion::process_external_surfaces(const Layer *lower_layer, const Poly
 
     Surfaces new_surfaces;
     {
-        // Merge top and bottom in a single collection.
-        surfaces_append(top, std::move(bottom));
         // Intersect the grown surfaces with the actual fill boundaries.
         Polygons bottom_polygons = to_polygons(bottom);
+        // Merge top and bottom in a single collection.
+        surfaces_append(top, std::move(bottom));
         for (size_t i = 0; i < top.size(); ++ i) {
             Surface &s1 = top[i];
             if (s1.empty())
@@ -422,9 +699,10 @@ void LayerRegion::process_external_surfaces(const Layer *lower_layer, const Poly
     m_fill_surfaces.surfaces = std::move(new_surfaces);
 
 #ifdef SLIC3R_DEBUG_SLICE_PROCESSING
-    export_region_fill_surfaces_to_svg_debug("3_process_external_surfaces-final");
+    export_region_fill_surfaces_to_svg_debug("4_process_external_surfaces-final");
 #endif /* SLIC3R_DEBUG_SLICE_PROCESSING */
 }
+#endif
 
 void LayerRegion::prepare_fill_surfaces()
 {

src/libslic3r/PerimeterGenerator.cpp

@@ -433,10 +433,12 @@ static ClipperLib_Z::Paths clip_extrusion(const ClipperLib_Z::Path &subject, con
     clipper.AddPath(subject, ClipperLib_Z::ptSubject, false);
     clipper.AddPaths(clip, ClipperLib_Z::ptClip, true);
 
-    ClipperLib_Z::PolyTree clipped_polytree;
     ClipperLib_Z::Paths    clipped_paths;
-    clipper.Execute(clipType, clipped_polytree, ClipperLib_Z::pftNonZero, ClipperLib_Z::pftNonZero);
+    {
-    ClipperLib_Z::PolyTreeToPaths(clipped_polytree, clipped_paths);
+        ClipperLib_Z::PolyTree clipped_polytree;
+        clipper.Execute(clipType, clipped_polytree, ClipperLib_Z::pftNonZero, ClipperLib_Z::pftNonZero);
+        ClipperLib_Z::PolyTreeToPaths(std::move(clipped_polytree), clipped_paths);
+    }
 
     // Clipped path could contain vertices from the clip with a Z coordinate equal to zero.
     // For those vertices, we must assign value based on the subject.

src/libslic3r/PlaceholderParser.cpp

@@ -185,75 +185,107 @@ namespace client
     template<typename Iterator>
     struct expr
     {
-                 expr() : type(TYPE_EMPTY) {}
+                 expr() {}
-        explicit expr(bool b) : type(TYPE_BOOL) { data.b = b; }
+        explicit expr(bool b) : m_type(TYPE_BOOL) { m_data.b = b; }
-        explicit expr(bool b, const Iterator &it_begin, const Iterator &it_end) : type(TYPE_BOOL), it_range(it_begin, it_end) { data.b = b; }
+        explicit expr(bool b, const Iterator &it_begin, const Iterator &it_end) : m_type(TYPE_BOOL), it_range(it_begin, it_end) { m_data.b = b; }
-        explicit expr(int i) : type(TYPE_INT) { data.i = i; }
+        explicit expr(int i) : m_type(TYPE_INT) { m_data.i = i; }
-        explicit expr(int i, const Iterator &it_begin, const Iterator &it_end) : type(TYPE_INT), it_range(it_begin, it_end) { data.i = i; }
+        explicit expr(int i, const Iterator &it_begin, const Iterator &it_end) : m_type(TYPE_INT), it_range(it_begin, it_end) { m_data.i = i; }
-        explicit expr(double d) : type(TYPE_DOUBLE) { data.d = d; }
+        explicit expr(double d) : m_type(TYPE_DOUBLE) { m_data.d = d; }
-        explicit expr(double d, const Iterator &it_begin, const Iterator &it_end) : type(TYPE_DOUBLE), it_range(it_begin, it_end) { data.d = d; }
+        explicit expr(double d, const Iterator &it_begin, const Iterator &it_end) : m_type(TYPE_DOUBLE), it_range(it_begin, it_end) { m_data.d = d; }
-        explicit expr(const char *s) : type(TYPE_STRING) { data.s = new std::string(s); }
+        explicit expr(const char *s) : m_type(TYPE_STRING) { m_data.s = new std::string(s); }
-        explicit expr(const std::string &s) : type(TYPE_STRING) { data.s = new std::string(s); }
+        explicit expr(const std::string &s) : m_type(TYPE_STRING) { m_data.s = new std::string(s); }
         explicit expr(const std::string &s, const Iterator &it_begin, const Iterator &it_end) : 
-            type(TYPE_STRING), it_range(it_begin, it_end) { data.s = new std::string(s); }
+            m_type(TYPE_STRING), it_range(it_begin, it_end) { m_data.s = new std::string(s); }
-                 expr(const expr &rhs) : type(rhs.type), it_range(rhs.it_range)
+                 expr(const expr &rhs) : m_type(rhs.type()), it_range(rhs.it_range)
-            { if (rhs.type == TYPE_STRING) data.s = new std::string(*rhs.data.s); else data.set(rhs.data); }
+            { if (rhs.type() == TYPE_STRING) m_data.s = new std::string(*rhs.m_data.s); else m_data.set(rhs.m_data); }
-        explicit expr(expr &&rhs) : type(rhs.type), it_range(rhs.it_range)
+        explicit expr(expr &&rhs) : expr(rhs, rhs.it_range.begin(), rhs.it_range.end()) {}
-            { data.set(rhs.data); rhs.type = TYPE_EMPTY; }
+        explicit expr(expr &&rhs, const Iterator &it_begin, const Iterator &it_end) : m_type(rhs.type()), it_range{ it_begin, it_end }
-        explicit expr(expr &&rhs, const Iterator &it_begin, const Iterator &it_end) : type(rhs.type), it_range(it_begin, it_end)
+        {   
-            { data.set(rhs.data); rhs.type = TYPE_EMPTY; }
+            m_data.set(rhs.m_data);
-        ~expr() { this->reset(); }
+            rhs.m_type = TYPE_EMPTY;
-
+        }
-        expr &operator=(const expr &rhs) 
+        expr &operator=(const expr &rhs)
         { 
-            this->type      = rhs.type;
+            if (rhs.type() == TYPE_STRING) {
-            this->it_range  = rhs.it_range;
+                this->set_s(rhs.s());
-            if (rhs.type == TYPE_STRING) 
+            } else  {
-                this->data.s = new std::string(*rhs.data.s);
+                m_type = rhs.type();
-            else 
+                m_data.set(rhs.m_data);
-                this->data.set(rhs.data);
+            }
-            return *this; 
+            this->it_range = rhs.it_range;
+            return *this;
         }
 
         expr &operator=(expr &&rhs) 
         { 
-            type            = rhs.type;
+            if (this != &rhs) {
-            this->it_range  = rhs.it_range;
+                this->reset();
-            data.set(rhs.data);
+                m_type          = rhs.type();
-            rhs.type        = TYPE_EMPTY;
+                this->it_range  = rhs.it_range;
+                m_data.set(rhs.m_data);
+                rhs.m_type      = TYPE_EMPTY;
+            }
             return *this;
         }
 
         void                reset()   
         { 
-            if (this->type == TYPE_STRING) 
+            if (this->type() == TYPE_STRING)
-                delete data.s;
+                delete m_data.s;
-            this->type = TYPE_EMPTY;
+            m_type = TYPE_EMPTY;
         }
 
-        bool&               b()       { return data.b; }
+        enum Type {
-        bool                b() const { return data.b; }
+            TYPE_EMPTY = 0,
-        void                set_b(bool v) { this->reset(); this->data.b = v; this->type = TYPE_BOOL; }
+            TYPE_BOOL,
-        int&                i()       { return data.i; }
+            TYPE_INT,
-        int                 i() const { return data.i; }
+            TYPE_DOUBLE,
-        void                set_i(int v) { this->reset(); this->data.i = v; this->type = TYPE_INT; }
+            TYPE_STRING,
-        int                 as_i() const { return (this->type == TYPE_INT) ? this->i() : int(this->d()); }
+        };
-        int                 as_i_rounded() const { return (this->type == TYPE_INT) ? this->i() : int(std::round(this->d())); }
+        Type                type() const { return m_type; }
-        double&             d()       { return data.d; }
+
-        double              d() const { return data.d; }
+        bool&               b()       { return m_data.b; }
-        void                set_d(double v) { this->reset(); this->data.d = v; this->type = TYPE_DOUBLE; }
+        bool                b() const { return m_data.b; }
-        double              as_d() const { return (this->type == TYPE_DOUBLE) ? this->d() : double(this->i()); }
+        void                set_b(bool v) { this->reset(); this->set_b_lite(v); }
-        std::string&        s()       { return *data.s; }
+        void                set_b_lite(bool v) { assert(this->type() != TYPE_STRING); Data tmp; tmp.b = v; m_data.set(tmp); m_type = TYPE_BOOL; }
-        const std::string&  s() const { return *data.s; }
+        int&                i()       { return m_data.i; }
-        void                set_s(const std::string &s) { this->reset(); this->data.s = new std::string(s); this->type = TYPE_STRING; }
+        int                 i() const { return m_data.i; }
-        void                set_s(std::string &&s) { this->reset(); this->data.s = new std::string(std::move(s)); this->type = TYPE_STRING; }
+        void                set_i(int v) { this->reset(); set_i_lite(v); }
+        void                set_i_lite(int v) { assert(this->type() != TYPE_STRING); Data tmp; tmp.i = v; m_data.set(tmp); m_type = TYPE_INT; }
+        int                 as_i() const { return this->type() == TYPE_INT ? this->i() : int(this->d()); }
+        int                 as_i_rounded() const { return this->type() == TYPE_INT ? this->i() : int(std::round(this->d())); }
+        double&             d()       { return m_data.d; }
+        double              d() const { return m_data.d; }
+        void                set_d(double v) { this->reset(); this->set_d_lite(v); }
+        void                set_d_lite(double v) { assert(this->type() != TYPE_STRING); Data tmp; tmp.d = v; m_data.set(tmp); m_type = TYPE_DOUBLE; }
+        double              as_d() const { return this->type() == TYPE_DOUBLE ? this->d() : double(this->i()); }
+        std::string&        s()       { return *m_data.s; }
+        const std::string&  s() const { return *m_data.s; }
+        void                set_s(const std::string &s) {
+            if (this->type() == TYPE_STRING)
+                *m_data.s = s;
+            else 
+                this->set_s_take_ownership(new std::string(s));
+        }
+        void                set_s(std::string &&s) {
+            if (this->type() == TYPE_STRING)
+                *m_data.s = std::move(s);
+            else
+                this->set_s_take_ownership(new std::string(std::move(s)));
+        }
+        void                set_s(const char *s) {
+            if (this->type() == TYPE_STRING)
+                *m_data.s = s;
+            else
+                this->set_s_take_ownership(new std::string(s));
+        }
         
         std::string         to_string() const 
         {
             std::string out;
-            switch (type) {
+            switch (this->type()) {
-			case TYPE_BOOL:   out = data.b ? "true" : "false"; break;
+			case TYPE_BOOL:   out = this->b() ? "true" : "false"; break;
-            case TYPE_INT:    out = std::to_string(data.i); break;
+            case TYPE_INT:    out = std::to_string(this->i()); break;
             case TYPE_DOUBLE: 
 #if 0
                 // The default converter produces trailing zeros after the decimal point.
@@ -263,48 +295,24 @@ namespace client
                 // It seems to be doing what the old boost::to_string() did.
 				{
 					std::ostringstream ss;
-					ss << data.d;
+					ss << this->d();
 					out = ss.str();
 				}
 #endif
 				break;
-            case TYPE_STRING: out = *data.s; break;
+            case TYPE_STRING: out = this->s(); break;
             default:          break;
             }
             return out;
         }
 
-        union Data {
-            // Raw image of the other data members.
-            // The C++ compiler will consider a possible aliasing of char* with any other union member,
-            // therefore copying the raw data is safe.
-            char         raw[8];
-            bool         b;
-            int          i;
-            double       d;
-            std::string *s;
-
-            // Copy the largest member variable through char*, which will alias with all other union members by default.
-            void set(const Data &rhs) { memcpy(this->raw, rhs.raw, sizeof(rhs.raw)); }
-        } data;
-
-        enum Type {
-            TYPE_EMPTY = 0,
-            TYPE_BOOL,
-            TYPE_INT,
-            TYPE_DOUBLE,
-            TYPE_STRING,
-        };
-
-        Type type;
-
         // Range of input iterators covering this expression.
         // Used for throwing parse exceptions.
         boost::iterator_range<Iterator>  it_range;
 
         expr unary_minus(const Iterator start_pos) const
         { 
-            switch (this->type) {
+            switch (this->type()) {
             case TYPE_INT :
                 return expr<Iterator>(- this->i(), start_pos, this->it_range.end());
             case TYPE_DOUBLE:
@@ -319,7 +327,7 @@ namespace client
 
         expr unary_integer(const Iterator start_pos) const
         { 
-            switch (this->type) {
+            switch (this->type()) {
             case TYPE_INT:
                 return expr<Iterator>(this->i(), start_pos, this->it_range.end());
             case TYPE_DOUBLE:
@@ -334,7 +342,7 @@ namespace client
 
         expr round(const Iterator start_pos) const
         { 
-            switch (this->type) {
+            switch (this->type()) {
             case TYPE_INT:
                 return expr<Iterator>(this->i(), start_pos, this->it_range.end());
             case TYPE_DOUBLE:
@@ -349,7 +357,7 @@ namespace client
 
         expr unary_not(const Iterator start_pos) const
         { 
-            switch (this->type) {
+            switch (this->type()) {
             case TYPE_BOOL:
                 return expr<Iterator>(! this->b(), start_pos, this->it_range.end());
             default:
@@ -362,23 +370,20 @@ namespace client
 
         expr &operator+=(const expr &rhs)
         { 
-            if (this->type == TYPE_STRING) {
+            if (this->type() == TYPE_STRING) {
                 // Convert the right hand side to string and append.
-                *this->data.s += rhs.to_string();
+                *m_data.s += rhs.to_string();
-            } else if (rhs.type == TYPE_STRING) {
+            } else if (rhs.type() == TYPE_STRING) {
                 // Conver the left hand side to string, append rhs.
-                this->data.s = new std::string(this->to_string() + rhs.s());
+                this->set_s(this->to_string() + rhs.s());
-                this->type = TYPE_STRING;
             } else {
                 const char *err_msg = "Cannot add non-numeric types.";
                 this->throw_if_not_numeric(err_msg);
                 rhs.throw_if_not_numeric(err_msg);
-                if (this->type == TYPE_DOUBLE || rhs.type == TYPE_DOUBLE) {
+                if (this->type() == TYPE_DOUBLE || rhs.type() == TYPE_DOUBLE)
-                    double d = this->as_d() + rhs.as_d();
+                    this->set_d_lite(this->as_d() + rhs.as_d());
-                    this->data.d = d;
+                else
-                    this->type = TYPE_DOUBLE;
+                    m_data.i += rhs.i();
-                } else
-                    this->data.i += rhs.i();
             }
             this->it_range = boost::iterator_range<Iterator>(this->it_range.begin(), rhs.it_range.end());
             return *this;
@@ -389,12 +394,10 @@ namespace client
             const char *err_msg = "Cannot subtract non-numeric types.";
             this->throw_if_not_numeric(err_msg);
             rhs.throw_if_not_numeric(err_msg);
-            if (this->type == TYPE_DOUBLE || rhs.type == TYPE_DOUBLE) {
+            if (this->type() == TYPE_DOUBLE || rhs.type() == TYPE_DOUBLE)
-                double d = this->as_d() - rhs.as_d();
+                this->set_d_lite(this->as_d() - rhs.as_d());
-                this->data.d = d;
+            else
-                this->type = TYPE_DOUBLE;
+                m_data.i -= rhs.i();
-            } else
-                this->data.i -= rhs.i();
             this->it_range = boost::iterator_range<Iterator>(this->it_range.begin(), rhs.it_range.end());
             return *this;
         }
@@ -404,12 +407,10 @@ namespace client
             const char *err_msg = "Cannot multiply with non-numeric type.";
             this->throw_if_not_numeric(err_msg);
             rhs.throw_if_not_numeric(err_msg);
-            if (this->type == TYPE_DOUBLE || rhs.type == TYPE_DOUBLE) {
+            if (this->type() == TYPE_DOUBLE || rhs.type() == TYPE_DOUBLE)
-                double d = this->as_d() * rhs.as_d();
+                this->set_d_lite(this->as_d() * rhs.as_d());
-                this->data.d = d;
+            else
-                this->type = TYPE_DOUBLE;
+                m_data.i *= rhs.i();
-            } else
-                this->data.i *= rhs.i();
             this->it_range = boost::iterator_range<Iterator>(this->it_range.begin(), rhs.it_range.end());
             return *this;
         }
@@ -418,14 +419,12 @@ namespace client
         {
             this->throw_if_not_numeric("Cannot divide a non-numeric type.");
             rhs.throw_if_not_numeric("Cannot divide with a non-numeric type.");
-            if ((rhs.type == TYPE_INT) ? (rhs.i() == 0) : (rhs.d() == 0.))
+            if (rhs.type() == TYPE_INT ? (rhs.i() == 0) : (rhs.d() == 0.))
                 rhs.throw_exception("Division by zero");
-            if (this->type == TYPE_DOUBLE || rhs.type == TYPE_DOUBLE) {
+            if (this->type() == TYPE_DOUBLE || rhs.type() == TYPE_DOUBLE)
-                double d = this->as_d() / rhs.as_d();
+                this->set_d_lite(this->as_d() / rhs.as_d());
-                this->data.d = d;
+            else
-                this->type = TYPE_DOUBLE;
+                m_data.i /= rhs.i();
-            } else
-                this->data.i /= rhs.i();
             this->it_range = boost::iterator_range<Iterator>(this->it_range.begin(), rhs.it_range.end());
             return *this;
         }
@@ -434,14 +433,12 @@ namespace client
         {
             this->throw_if_not_numeric("Cannot divide a non-numeric type.");
             rhs.throw_if_not_numeric("Cannot divide with a non-numeric type.");
-            if ((rhs.type == TYPE_INT) ? (rhs.i() == 0) : (rhs.d() == 0.))
+            if (rhs.type() == TYPE_INT ? (rhs.i() == 0) : (rhs.d() == 0.))
                 rhs.throw_exception("Division by zero");
-            if (this->type == TYPE_DOUBLE || rhs.type == TYPE_DOUBLE) {
+            if (this->type() == TYPE_DOUBLE || rhs.type() == TYPE_DOUBLE)
-                double d = std::fmod(this->as_d(), rhs.as_d());
+                this->set_d_lite(std::fmod(this->as_d(), rhs.as_d()));
-                this->data.d = d;
+            else
-                this->type = TYPE_DOUBLE;
+                m_data.i %= rhs.i();
-            } else
-                this->data.i %= rhs.i();
             this->it_range = boost::iterator_range<Iterator>(this->it_range.begin(), rhs.it_range.end());
             return *this;
         }
@@ -453,14 +450,14 @@ namespace client
 
         static void evaluate_boolean(expr &self, bool &out)
         {
-            if (self.type != TYPE_BOOL)
+            if (self.type() != TYPE_BOOL)
                 self.throw_exception("Not a boolean expression");
             out = self.b();
         }
 
         static void evaluate_boolean_to_string(expr &self, std::string &out)
         {
-            if (self.type != TYPE_BOOL)
+            if (self.type() != TYPE_BOOL)
                 self.throw_exception("Not a boolean expression");
             out = self.b() ? "true" : "false";
         }
@@ -469,31 +466,31 @@ namespace client
         static void compare_op(expr &lhs, expr &rhs, char op, bool invert)
         {
             bool value = false;
-            if ((lhs.type == TYPE_INT || lhs.type == TYPE_DOUBLE) &&
+            if ((lhs.type() == TYPE_INT || lhs.type() == TYPE_DOUBLE) &&
-                (rhs.type == TYPE_INT || rhs.type == TYPE_DOUBLE)) {
+                (rhs.type() == TYPE_INT || rhs.type() == TYPE_DOUBLE)) {
                 // Both types are numeric.
                 switch (op) {
                     case '=':
-                        value = (lhs.type == TYPE_DOUBLE || rhs.type == TYPE_DOUBLE) ? 
+                        value = (lhs.type() == TYPE_DOUBLE || rhs.type() == TYPE_DOUBLE) ? 
                             (std::abs(lhs.as_d() - rhs.as_d()) < 1e-8) : (lhs.i() == rhs.i());
                         break;
                     case '<':
-                        value = (lhs.type == TYPE_DOUBLE || rhs.type == TYPE_DOUBLE) ? 
+                        value = (lhs.type() == TYPE_DOUBLE || rhs.type() == TYPE_DOUBLE) ? 
                             (lhs.as_d() < rhs.as_d()) : (lhs.i() < rhs.i());
                         break;
                     case '>':
                     default:
-                        value = (lhs.type == TYPE_DOUBLE || rhs.type == TYPE_DOUBLE) ? 
+                        value = (lhs.type() == TYPE_DOUBLE || rhs.type() == TYPE_DOUBLE) ? 
                             (lhs.as_d() > rhs.as_d()) : (lhs.i() > rhs.i());
                         break;
                 }
-            } else if (lhs.type == TYPE_BOOL && rhs.type == TYPE_BOOL) {
+            } else if (lhs.type() == TYPE_BOOL && rhs.type() == TYPE_BOOL) {
                 // Both type are bool.
                 if (op != '=')
                     boost::throw_exception(qi::expectation_failure<Iterator>(
                         lhs.it_range.begin(), rhs.it_range.end(), spirit::info("*Cannot compare the types.")));
                 value = lhs.b() == rhs.b();
-            } else if (lhs.type == TYPE_STRING || rhs.type == TYPE_STRING) {
+            } else if (lhs.type() == TYPE_STRING || rhs.type() == TYPE_STRING) {
                 // One type is string, the other could be converted to string.
                 value = (op == '=') ? (lhs.to_string() == rhs.to_string()) : 
                         (op == '<') ? (lhs.to_string() < rhs.to_string()) : (lhs.to_string() > rhs.to_string());
@@ -502,8 +499,7 @@ namespace client
                     lhs.it_range.begin(), rhs.it_range.end(), spirit::info("*Cannot compare the types.")));
             }
             lhs.reset();
-            lhs.type = TYPE_BOOL;
+            lhs.set_b_lite(invert ? ! value : value);
-            lhs.data.b = invert ? ! value : value;
         }
         // Compare operators, store the result into lhs.
         static void equal    (expr &lhs, expr &rhs) { compare_op(lhs, rhs, '=', false); }
@@ -528,15 +524,14 @@ namespace client
         { 
             throw_if_not_numeric(param1);
             throw_if_not_numeric(param2);
-            if (param1.type == TYPE_DOUBLE || param2.type == TYPE_DOUBLE) {
+            if (param1.type() == TYPE_DOUBLE || param2.type() == TYPE_DOUBLE) {
                 double d = 0.;
                 switch (fun) {
                     case FUNCTION_MIN:  d = std::min(param1.as_d(), param2.as_d()); break;
                     case FUNCTION_MAX:  d = std::max(param1.as_d(), param2.as_d()); break;
                     default: param1.throw_exception("Internal error: invalid function");
                 }
-                param1.data.d = d;
+                param1.set_d_lite(d);
-                param1.type = TYPE_DOUBLE;
             } else {
                 int i = 0;
                 switch (fun) {
@@ -544,8 +539,7 @@ namespace client
                     case FUNCTION_MAX:  i = std::max(param1.as_i(), param2.as_i()); break;
                     default: param1.throw_exception("Internal error: invalid function");
                 }
-                param1.data.i = i;
+                param1.set_i_lite(i);
-                param1.type = TYPE_INT;
             }
         }
         // Store the result into param1.
@@ -557,13 +551,10 @@ namespace client
         { 
             throw_if_not_numeric(param1);
             throw_if_not_numeric(param2);
-            if (param1.type == TYPE_DOUBLE || param2.type == TYPE_DOUBLE) {
+            if (param1.type() == TYPE_DOUBLE || param2.type() == TYPE_DOUBLE)
-                param1.data.d = std::uniform_real_distribution<>(param1.as_d(), param2.as_d())(rng);
+                param1.set_d_lite(std::uniform_real_distribution<>(param1.as_d(), param2.as_d())(rng));
-                param1.type   = TYPE_DOUBLE;
+            else
-            } else {
+                param1.set_i_lite(std::uniform_int_distribution<>(param1.as_i(), param2.as_i())(rng));
-                param1.data.i = std::uniform_int_distribution<>(param1.as_i(), param2.as_i())(rng);
-                param1.type   = TYPE_INT;
-            }
         }
 
         // Store the result into param1.
@@ -572,10 +563,10 @@ namespace client
         static void digits(expr &param1, expr &param2, expr &param3)
         { 
             throw_if_not_numeric(param1);
-            if (param2.type != TYPE_INT)
+            if (param2.type() != TYPE_INT)
                 param2.throw_exception("digits: second parameter must be integer");
-            bool has_decimals = param3.type != TYPE_EMPTY;
+            bool has_decimals = param3.type() != TYPE_EMPTY;
-            if (has_decimals && param3.type != TYPE_INT)
+            if (has_decimals && param3.type() != TYPE_INT)
                 param3.throw_exception("digits: third parameter must be integer");
 
             char buf[256];
@@ -593,7 +584,7 @@ namespace client
         static void regex_op(expr &lhs, boost::iterator_range<Iterator> &rhs, char op)
         {
             const std::string *subject  = nullptr;
-            if (lhs.type == TYPE_STRING) {
+            if (lhs.type() == TYPE_STRING) {
                 // One type is string, the other could be converted to string.
                 subject = &lhs.s();
             } else {
@@ -604,9 +595,7 @@ namespace client
                 bool result = SLIC3R_REGEX_NAMESPACE::regex_match(*subject, SLIC3R_REGEX_NAMESPACE::regex(pattern));
                 if (op == '!')
                     result = ! result;
-                lhs.reset();
+                lhs.set_b(result);
-                lhs.type = TYPE_BOOL;
-                lhs.data.b = result;
             } catch (SLIC3R_REGEX_NAMESPACE::regex_error &ex) {
                 // Syntax error in the regular expression
                 boost::throw_exception(qi::expectation_failure<Iterator>(
@@ -620,21 +609,20 @@ namespace client
         static void logical_op(expr &lhs, expr &rhs, char op)
         {
             bool value = false;
-            if (lhs.type == TYPE_BOOL && rhs.type == TYPE_BOOL) {
+            if (lhs.type() == TYPE_BOOL && rhs.type() == TYPE_BOOL) {
                 value = (op == '|') ? (lhs.b() || rhs.b()) : (lhs.b() && rhs.b());
             } else {
                 boost::throw_exception(qi::expectation_failure<Iterator>(
                     lhs.it_range.begin(), rhs.it_range.end(), spirit::info("*Cannot apply logical operation to non-boolean operators.")));
             }
-            lhs.type   = TYPE_BOOL;
+            lhs.set_b_lite(value);
-            lhs.data.b = value;
         }
         static void logical_or (expr &lhs, expr &rhs) { logical_op(lhs, rhs, '|'); }
         static void logical_and(expr &lhs, expr &rhs) { logical_op(lhs, rhs, '&'); }
 
         static void ternary_op(expr &lhs, expr &rhs1, expr &rhs2)
         {
-            if (lhs.type != TYPE_BOOL)
+            if (lhs.type() != TYPE_BOOL)
                 lhs.throw_exception("Not a boolean expression");
             if (lhs.b())
                 lhs = std::move(rhs1);
@@ -658,9 +646,25 @@ namespace client
 
         void throw_if_not_numeric(const char *message) const 
         {
-            if (this->type != TYPE_INT && this->type != TYPE_DOUBLE)
+            if (this->type() != TYPE_INT && this->type() != TYPE_DOUBLE)
                 this->throw_exception(message);
         }
+
+    private:
+        // This object will take ownership of the parameter string object "s".
+        void        set_s_take_ownership(std::string* s) { assert(this->type() != TYPE_STRING); Data tmp; tmp.s = s; m_data.set(tmp); m_type = TYPE_STRING; }
+
+        Type        m_type = TYPE_EMPTY;
+
+        union Data {
+            bool         b;
+            int          i;
+            double       d;
+            std::string *s;
+
+            // Copy the largest member variable through char*, which will alias with all other union members by default.
+            void set(const Data &rhs) { memcpy(this, &rhs, sizeof(rhs)); }
+        } m_data;
     };
 
     template<typename ITERATOR>
@@ -668,7 +672,7 @@ namespace client
     {
         typedef expr<ITERATOR> Expr;
         os << std::string(expression.it_range.begin(), expression.it_range.end()) << " - ";
-        switch (expression.type) {
+        switch (expression.type()) {
         case Expr::TYPE_EMPTY:    os << "empty"; break;
         case Expr::TYPE_BOOL:     os << "bool ("   << expression.b() << ")"; break;
         case Expr::TYPE_INT:      os << "int ("    << expression.i() << ")"; break;
@@ -802,6 +806,7 @@ namespace client
             case coInt:     output.set_i(opt.opt->getInt());     break;
             case coString:  output.set_s(static_cast<const ConfigOptionString*>(opt.opt)->value); break;
             case coPercent: output.set_d(opt.opt->getFloat());   break;
+            case coEnum:
             case coPoint:   output.set_s(opt.opt->serialize());  break;
             case coBool:    output.set_b(opt.opt->getBool());    break;
             case coFloatOrPercent:
@@ -869,6 +874,7 @@ namespace client
             case coPercents: output.set_d(static_cast<const ConfigOptionPercents*>(opt.opt)->values[idx]); break;
             case coPoints:   output.set_s(to_string(static_cast<const ConfigOptionPoints  *>(opt.opt)->values[idx])); break;
             case coBools:    output.set_b(static_cast<const ConfigOptionBools   *>(opt.opt)->values[idx] != 0); break;
+            //case coEnums:    output.set_s(opt.opt->vserialize()[idx]); break;
             default:
                 ctx->throw_exception("Unknown vector variable type", opt.it_range);
             }
@@ -912,7 +918,7 @@ namespace client
         template <typename Iterator>
         static void evaluate_index(expr<Iterator> &expr_index, int &output)
         {
-            if (expr_index.type != expr<Iterator>::TYPE_INT)                
+            if (expr_index.type() != expr<Iterator>::TYPE_INT)                
                 expr_index.throw_exception("Non-integer index is not allowed to address a vector variable.");
             output = expr_index.i();
         }

src/libslic3r/PlaceholderParser.hpp

@@ -5,6 +5,7 @@
 #include <map>
 #include <random>
 #include <string>
+#include <string_view>
 #include <vector>
 #include "PrintConfig.hpp"
 
@@ -38,6 +39,8 @@ public:
 
     // Add new ConfigOption values to m_config.
     void set(const std::string &key, const std::string &value)  { this->set(key, new ConfigOptionString(value)); }
+    void set(const std::string &key, std::string_view value)    { this->set(key, new ConfigOptionString(std::string(value))); }
+    void set(const std::string &key, const char *value)         { this->set(key, new ConfigOptionString(value)); }
     void set(const std::string &key, int value)                 { this->set(key, new ConfigOptionInt(value)); }
     void set(const std::string &key, unsigned int value)        { this->set(key, int(value)); }
     void set(const std::string &key, bool value)                { this->set(key, new ConfigOptionBool(value)); }

src/libslic3r/Point.cpp

@@ -84,18 +84,28 @@ Points collect_duplicates(Points pts /* Copy */)
     return duplicits;
 }
 
+template<bool IncludeBoundary>
 BoundingBox get_extents(const Points &pts)
 { 
-    return BoundingBox(pts);
+    BoundingBox out;
+    BoundingBox::construct<IncludeBoundary>(out, pts.begin(), pts.end());
+    return out;
 }
+template BoundingBox get_extents<false>(const Points &pts);
+template BoundingBox get_extents<true>(const Points &pts);
 
+// if IncludeBoundary, then a bounding box is defined even for a single point.
+// otherwise a bounding box is only defined if it has a positive area.
+template<bool IncludeBoundary>
 BoundingBox get_extents(const std::vector<Points> &pts)
 {
     BoundingBox bbox;
     for (const Points &p : pts)
-        bbox.merge(get_extents(p));
+        bbox.merge(get_extents<IncludeBoundary>(p));
     return bbox;
 }
+template BoundingBox get_extents<false>(const std::vector<Points> &pts);
+template BoundingBox get_extents<true>(const std::vector<Points> &pts);
 
 BoundingBoxf get_extents(const std::vector<Vec2d> &pts)
 {

src/libslic3r/Point.hpp

@@ -237,8 +237,20 @@ inline Point lerp(const Point &a, const Point &b, double t)
     return ((1. - t) * a.cast<double>() + t * b.cast<double>()).cast<coord_t>();
 }
 
+// if IncludeBoundary, then a bounding box is defined even for a single point.
+// otherwise a bounding box is only defined if it has a positive area.
+template<bool IncludeBoundary = false>
 BoundingBox get_extents(const Points &pts);
+extern template BoundingBox get_extents<false>(const Points &pts);
+extern template BoundingBox get_extents<true>(const Points &pts);
+
+// if IncludeBoundary, then a bounding box is defined even for a single point.
+// otherwise a bounding box is only defined if it has a positive area.
+template<bool IncludeBoundary = false>
 BoundingBox get_extents(const std::vector<Points> &pts);
+extern template BoundingBox get_extents<false>(const std::vector<Points> &pts);
+extern template BoundingBox get_extents<true>(const std::vector<Points> &pts);
+
 BoundingBoxf get_extents(const std::vector<Vec2d> &pts);
 
 int nearest_point_index(const Points &points, const Point &pt);

src/libslic3r/Polyline.cpp

@@ -292,6 +292,19 @@ void ThickPolyline::clip_end(double distance)
     assert(this->width.size() == (this->points.size() - 1) * 2);
 }
 
+void ThickPolyline::start_at_index(int index)
+{
+    assert(index >= 0 && index < this->points.size());
+    assert(this->points.front() == this->points.back() && this->width.front() == this->width.back());
+    if (index != 0 && index != (this->points.size() - 1) && this->points.front() == this->points.back() && this->width.front() == this->width.back()) {
+        this->points.pop_back();
+        assert(this->points.size() * 2 == this->width.size());
+        std::rotate(this->points.begin(), this->points.begin() + index, this->points.end());
+        std::rotate(this->width.begin(), this->width.begin() + 2 * index, this->width.end());
+        this->points.emplace_back(this->points.front());
+    }
+}
+
 double Polyline3::length() const
 {
     double l = 0;

src/libslic3r/Polyline.hpp

@@ -153,6 +153,25 @@ inline void polylines_append(Polylines &dst, Polylines &&src)
     }
 }
 
+// Merge polylines at their respective end points.
+// dst_first: the merge point is at dst.begin() or dst.end()?
+// src_first: the merge point is at src.begin() or src.end()?
+// The orientation of the resulting polyline is unknown, the output polyline may start
+// either with src piece or dst piece.
+template<typename PointType>
+inline void polylines_merge(std::vector<PointType> &dst, bool dst_first, std::vector<PointType> &&src, bool src_first)
+{
+    if (dst_first) {
+        if (src_first)
+            std::reverse(dst.begin(), dst.end());
+        else
+            std::swap(dst, src);
+    } else if (! src_first)
+        std::reverse(src.begin(), src.end());
+    // Merge src into dst.
+    append(dst, std::move(src));
+}
+
 const Point& leftmost_point(const Polylines &polylines);
 
 bool remove_degenerate(Polylines &polylines);
@@ -166,6 +185,7 @@ struct ThickPolyline {
 
     const Point& first_point()  const { return this->points.front(); }
     const Point& last_point()   const { return this->points.back(); }
+    size_t       size()         const { return this->points.size(); }
     bool         is_valid()     const { return this->points.size() >= 2; }
     double       length()       const { return Slic3r::length(this->points); }
 
@@ -179,6 +199,11 @@ struct ThickPolyline {
 
     void clip_end(double distance);
 
+    // Make this closed ThickPolyline starting in the specified index.
+    // Be aware that this method can be applicable just for closed ThickPolyline.
+    // On open ThickPolyline make no effect.
+    void start_at_index(int index);
+
     Points                  points;
     std::vector<coordf_t>   width;
     std::pair<bool,bool>    endpoints { false, false };

src/libslic3r/Preset.cpp

@@ -786,7 +786,7 @@ std::pair<Preset*, bool> PresetCollection::load_external_preset(
 {
     // Load the preset over a default preset, so that the missing fields are filled in from the default preset.
     DynamicPrintConfig cfg(this->default_preset_for(combined_config).config);
-    t_config_option_keys keys = std::move(cfg.keys());
+    t_config_option_keys keys = cfg.keys();
     cfg.apply_only(combined_config, keys, true);
     std::string                 &inherits = Preset::inherits(cfg);
     if (select == LoadAndSelect::Never) {

src/libslic3r/PrintConfig.cpp

@@ -591,7 +591,7 @@ void PrintConfigDef::init_fff_params()
         "Fan speeds for overhang sizes in between are calculated via linear interpolation. ");
 
     def           = this->add("overhang_fan_speed_0", coInts);
-    def->label    = L("speed for 0\% overlap (bridge)");
+    def->label    = L("speed for 0% overlap (bridge)");
     def->tooltip  = fan_speed_setting_description;
     def->sidetext = L("%");
     def->min      = 0;
@@ -600,7 +600,7 @@ void PrintConfigDef::init_fff_params()
     def->set_default_value(new ConfigOptionInts{0});
 
     def           = this->add("overhang_fan_speed_1", coInts);
-    def->label    = L("speed for 25\% overlap");
+    def->label    = L("speed for 25% overlap");
     def->tooltip  = fan_speed_setting_description;
     def->sidetext = L("%");
     def->min      = 0;
@@ -609,7 +609,7 @@ void PrintConfigDef::init_fff_params()
     def->set_default_value(new ConfigOptionInts{0});
 
     def           = this->add("overhang_fan_speed_2", coInts);
-    def->label    = L("speed for 50\% overlap");
+    def->label    = L("speed for 50% overlap");
     def->tooltip  = fan_speed_setting_description;
     def->sidetext = L("%");
     def->min      = 0;
@@ -618,7 +618,7 @@ void PrintConfigDef::init_fff_params()
     def->set_default_value(new ConfigOptionInts{0});
 
     def           = this->add("overhang_fan_speed_3", coInts);
-    def->label    = L("speed for 75\% overlap");
+    def->label    = L("speed for 75% overlap");
     def->tooltip  = fan_speed_setting_description;
     def->sidetext = L("%");
     def->min      = 0;

src/libslic3r/PrintConfig.hpp

@@ -60,6 +60,7 @@ enum InfillPattern : int {
     ipRectilinear, ipMonotonic, ipMonotonicLines, ipAlignedRectilinear, ipGrid, ipTriangles, ipStars, ipCubic, ipLine, ipConcentric, ipHoneycomb, ip3DHoneycomb,
     ipGyroid, ipHilbertCurve, ipArchimedeanChords, ipOctagramSpiral, ipAdaptiveCubic, ipSupportCubic, ipSupportBase,
     ipLightning,
+    ipEnsuring,
     ipCount,
 };
 
@@ -162,6 +163,7 @@ CONFIG_OPTION_ENUM_DECLARE_STATIC_MAPS(GCodeThumbnailsFormat)
 CONFIG_OPTION_ENUM_DECLARE_STATIC_MAPS(ForwardCompatibilitySubstitutionRule)
 CONFIG_OPTION_ENUM_DECLARE_STATIC_MAPS(PerimeterGeneratorType)
 
+
 #undef CONFIG_OPTION_ENUM_DECLARE_STATIC_MAPS
 
 // Defines each and every confiuration option of Slic3r, including the properties of the GUI dialogs.

src/libslic3r/SupportMaterial.cpp

@@ -4755,4 +4755,3 @@ sub clip_with_shape {
 */
 
 } // namespace Slic3r
-

src/libslic3r/SupportSpotsGenerator.cpp

@@ -901,7 +901,7 @@ std::tuple<SupportPoints, PartialObjects> check_stability(const PrintObject *po,
                                                                   params)) {
                                 if (bridge.support_point_generated.has_value()) {
                                     reckon_new_support_point(*bridge.support_point_generated, create_support_point_position(bridge.b),
-                                                             -EPSILON, Vec2f::Zero());
+                                                             float(-EPSILON), Vec2f::Zero());
                                 }
                             }
                         }
@@ -916,7 +916,7 @@ std::tuple<SupportPoints, PartialObjects> check_stability(const PrintObject *po,
                                                                                          params);
                     for (const ExtrusionLine &perim : perims) {
                         if (perim.support_point_generated.has_value()) {
-                            reckon_new_support_point(*perim.support_point_generated, create_support_point_position(perim.b), -EPSILON,
+                            reckon_new_support_point(*perim.support_point_generated, create_support_point_position(perim.b), float(-EPSILON),
                                                      Vec2f::Zero());
                         }
                         if (perim.is_external_perimeter()) {

src/libslic3r/SupportSpotsGenerator.hpp

@@ -145,6 +145,7 @@ struct PartialObject
 
 using PartialObjects = std::vector<PartialObject>;
 
+// Both support points and partial objects are sorted from the lowest z to the highest
 std::tuple<SupportPoints, PartialObjects> full_search(const PrintObject *po, const PrintTryCancel& cancel_func, const Params &params);
 
 void estimate_supports_malformations(std::vector<SupportLayer *> &layers, float supports_flow_width, const Params &params);

src/libslic3r/Surface.hpp

@@ -33,40 +33,31 @@ class Surface
 public:
     SurfaceType     surface_type;
     ExPolygon       expolygon;
-    double          thickness;          // in mm
+    double          thickness        { -1 };  // in mm
-    unsigned short  thickness_layers;   // in layers
+    unsigned short  thickness_layers {  1 };  // in layers
-    double          bridge_angle;       // in radians, ccw, 0 = East, only 0+ (negative means undefined)
+    double          bridge_angle     { -1. }; // in radians, ccw, 0 = East, only 0+ (negative means undefined)
-    unsigned short  extra_perimeters;
+    unsigned short  extra_perimeters {  0 };
     
-    Surface(const Slic3r::Surface &rhs)
+    Surface(const Slic3r::Surface &rhs) :
-        : surface_type(rhs.surface_type), expolygon(rhs.expolygon),
+        surface_type(rhs.surface_type), expolygon(rhs.expolygon),
-            thickness(rhs.thickness), thickness_layers(rhs.thickness_layers), 
+        thickness(rhs.thickness), thickness_layers(rhs.thickness_layers), 
-            bridge_angle(rhs.bridge_angle), extra_perimeters(rhs.extra_perimeters)
+        bridge_angle(rhs.bridge_angle), extra_perimeters(rhs.extra_perimeters) {}
-        {};
+    Surface(SurfaceType surface_type, const ExPolygon &expolygon) : 
-
+        surface_type(surface_type), expolygon(expolygon) {}
-    Surface(SurfaceType _surface_type, const ExPolygon &_expolygon)
+    Surface(const Surface &templ, const ExPolygon &expolygon) :
-        : surface_type(_surface_type), expolygon(_expolygon),
+        surface_type(templ.surface_type), expolygon(expolygon),
-            thickness(-1), thickness_layers(1), bridge_angle(-1), extra_perimeters(0)
+        thickness(templ.thickness), thickness_layers(templ.thickness_layers),
-        {};
+        bridge_angle(templ.bridge_angle), extra_perimeters(templ.extra_perimeters) {}
-    Surface(const Surface &other, const ExPolygon &_expolygon)
+    Surface(Surface &&rhs) :
-        : surface_type(other.surface_type), expolygon(_expolygon),
+        surface_type(rhs.surface_type), expolygon(std::move(rhs.expolygon)),
-            thickness(other.thickness), thickness_layers(other.thickness_layers), 
+        thickness(rhs.thickness), thickness_layers(rhs.thickness_layers), 
-            bridge_angle(other.bridge_angle), extra_perimeters(other.extra_perimeters)
+        bridge_angle(rhs.bridge_angle), extra_perimeters(rhs.extra_perimeters) {}
-        {};
+    Surface(SurfaceType surface_type, ExPolygon &&expolygon) : 
-    Surface(Surface &&rhs)
+        surface_type(surface_type), expolygon(std::move(expolygon)) {}
-        : surface_type(rhs.surface_type), expolygon(std::move(rhs.expolygon)),
+    Surface(const Surface &templ, ExPolygon &&expolygon) :
-            thickness(rhs.thickness), thickness_layers(rhs.thickness_layers), 
+        surface_type(templ.surface_type), expolygon(std::move(expolygon)),
-            bridge_angle(rhs.bridge_angle), extra_perimeters(rhs.extra_perimeters)
+            thickness(templ.thickness), thickness_layers(templ.thickness_layers), 
-        {};
+            bridge_angle(templ.bridge_angle), extra_perimeters(templ.extra_perimeters) {}
-    Surface(SurfaceType _surface_type, ExPolygon &&_expolygon)
-        : surface_type(_surface_type), expolygon(std::move(_expolygon)),
-            thickness(-1), thickness_layers(1), bridge_angle(-1), extra_perimeters(0)
-        {};
-    Surface(const Surface &other, ExPolygon &&_expolygon)
-        : surface_type(other.surface_type), expolygon(std::move(_expolygon)),
-            thickness(other.thickness), thickness_layers(other.thickness_layers), 
-            bridge_angle(other.bridge_angle), extra_perimeters(other.extra_perimeters)
-        {};
 
     Surface& operator=(const Surface &rhs)
     {

src/libslic3r/SurfaceCollection.cpp

@@ -51,16 +51,12 @@ SurfacesPtr SurfaceCollection::filter_by_type(const SurfaceType type) const
     return ss;
 }
 
-SurfacesPtr SurfaceCollection::filter_by_types(const SurfaceType *types, int ntypes) const
+SurfacesPtr SurfaceCollection::filter_by_types(std::initializer_list<SurfaceType> types) const
 {
     SurfacesPtr ss;
     for (const Surface &surface : this->surfaces)
-        for (int i = 0; i < ntypes; ++ i) {
+        if (std::find(types.begin(), types.end(), surface.surface_type) != types.end())
-            if (surface.surface_type == types[i]) {
+            ss.push_back(&surface);
-                ss.push_back(&surface);
-                break;
-            }
-        }
     return ss;
 }
 
@@ -85,23 +81,15 @@ void SurfaceCollection::keep_type(const SurfaceType type)
         surfaces.erase(surfaces.begin() + j, surfaces.end());
 }
 
-void SurfaceCollection::keep_types(const SurfaceType *types, int ntypes)
+void SurfaceCollection::keep_types(std::initializer_list<SurfaceType> types)
 {
     size_t j = 0;
-    for (size_t i = 0; i < surfaces.size(); ++ i) {
+    for (size_t i = 0; i < surfaces.size(); ++ i)
-        bool keep = false;
+        if (std::find(types.begin(), types.end(), surfaces[i].surface_type) != types.end()) {
-        for (int k = 0; k < ntypes; ++ k) {
-            if (surfaces[i].surface_type == types[k]) {
-                keep = true;
-                break;
-            }
-        }
-        if (keep) {
             if (j < i)
                 std::swap(surfaces[i], surfaces[j]);
             ++ j;
         }
-    }
     if (j < surfaces.size())
         surfaces.erase(surfaces.begin() + j, surfaces.end());
 }
@@ -136,23 +124,15 @@ void SurfaceCollection::remove_type(const SurfaceType type, ExPolygons *polygons
         surfaces.erase(surfaces.begin() + j, surfaces.end());
 }
 
-void SurfaceCollection::remove_types(const SurfaceType *types, int ntypes)
+void SurfaceCollection::remove_types(std::initializer_list<SurfaceType> types)
 {
     size_t j = 0;
-    for (size_t i = 0; i < surfaces.size(); ++ i) {
+    for (size_t i = 0; i < surfaces.size(); ++ i)
-        bool remove = false;
+        if (std::find(types.begin(), types.end(), surfaces[i].surface_type) == types.end()) {
-        for (int k = 0; k < ntypes; ++ k) {
-            if (surfaces[i].surface_type == types[k]) {
-                remove = true;
-                break;
-            }
-        }
-        if (! remove) {
             if (j < i)
                 std::swap(surfaces[i], surfaces[j]);
             ++ j;
         }
-    }
     if (j < surfaces.size())
         surfaces.erase(surfaces.begin() + j, surfaces.end());
 }

src/libslic3r/SurfaceCollection.hpp

@@ -3,6 +3,7 @@
 
 #include "libslic3r.h"
 #include "Surface.hpp"
+#include <initializer_list>
 #include <vector>
 
 namespace Slic3r {
@@ -27,11 +28,11 @@ public:
         return false;
     }
     SurfacesPtr filter_by_type(const SurfaceType type) const;
-    SurfacesPtr filter_by_types(const SurfaceType *types, int ntypes) const;
+    SurfacesPtr filter_by_types(std::initializer_list<SurfaceType> types) const;
     void keep_type(const SurfaceType type);
-    void keep_types(const SurfaceType *types, int ntypes);
+    void keep_types(std::initializer_list<SurfaceType> types);
     void remove_type(const SurfaceType type);
-    void remove_types(const SurfaceType *types, int ntypes);
+    void remove_types(std::initializer_list<SurfaceType> types);
     void filter_by_type(SurfaceType type, Polygons *polygons) const;
     void remove_type(const SurfaceType type, ExPolygons *polygons);
     void set_type(SurfaceType type) {

src/libslic3r/TreeSupport.cpp

@@ -2421,7 +2421,6 @@ static void merge_influence_areas(
     tbb::parallel_for(tbb::blocked_range<size_t>(0, num_buckets_initial),
         [&](const tbb::blocked_range<size_t> &range) {
         for (size_t idx = range.begin(); idx < range.end(); ++ idx) {
-            const size_t bucket_pair_idx = idx * 2;
             // Merge bucket_count adjacent to each other, merging uneven bucket numbers into even buckets
             buckets[idx].second = merge_influence_areas_leaves(volumes, config, layer_idx, buckets[idx].first, buckets[idx].second);
             throw_on_cancel();
@@ -4012,8 +4011,12 @@ static indexed_triangle_set draw_branches(
                         // Only one link points to a node above from below.
                         assert(!(++it != map_downwards_old.end() && it->first == &elem));
                     }
-                    const SupportElement *pchild = child == -1 ? nullptr : &move_bounds[layer_idx - 1][child];
+#ifndef NDEBUG
-                    assert(pchild ? pchild->state.result_on_layer_is_set() : elem.state.target_height > layer_idx);
+                    {
+                        const SupportElement *pchild = child == -1 ? nullptr : &move_bounds[layer_idx - 1][child];
+                        assert(pchild ? pchild->state.result_on_layer_is_set() : elem.state.target_height > layer_idx);
+                    }
+#endif // NDEBUG
                 }
                 for (int32_t parent_idx : elem.parents) {
                     SupportElement &parent = (*layer_above)[parent_idx];
@@ -4078,19 +4081,22 @@ static indexed_triangle_set draw_branches(
                     partial_mesh.clear();
                     extrude_branch(path, config, slicing_params, move_bounds, partial_mesh);
 #if 0
-                    char fname[2048];
+                    {
-                    sprintf(fname, "d:\\temp\\meshes\\tree-raw-%d.obj", ++ irun);
+                        char fname[2048];
-                    its_write_obj(partial_mesh, fname);
+                        static int irun = 0;
-#if 0
+                        sprintf(fname, "d:\\temp\\meshes\\tree-raw-%d.obj", ++ irun);
-                    temp_mesh.clear();
+                        its_write_obj(partial_mesh, fname);
-                    cut_mesh(partial_mesh, layer_z(slicing_params, path.back()->state.layer_idx) + EPSILON, nullptr, &temp_mesh, false);
+    #if 0
-                    sprintf(fname, "d:\\temp\\meshes\\tree-trimmed1-%d.obj", irun);
+                        temp_mesh.clear();
-                    its_write_obj(temp_mesh, fname);
+                        cut_mesh(partial_mesh, layer_z(slicing_params, path.back()->state.layer_idx) + EPSILON, nullptr, &temp_mesh, false);
-                    partial_mesh.clear();
+                        sprintf(fname, "d:\\temp\\meshes\\tree-trimmed1-%d.obj", irun);
-                    cut_mesh(temp_mesh, layer_z(slicing_params, path.front()->state.layer_idx) - EPSILON, &partial_mesh, nullptr, false);
+                        its_write_obj(temp_mesh, fname);
-                    sprintf(fname, "d:\\temp\\meshes\\tree-trimmed2-%d.obj", irun);
+                        partial_mesh.clear();
-#endif
+                        cut_mesh(temp_mesh, layer_z(slicing_params, path.front()->state.layer_idx) - EPSILON, &partial_mesh, nullptr, false);
-                    its_write_obj(partial_mesh, fname);
+                        sprintf(fname, "d:\\temp\\meshes\\tree-trimmed2-%d.obj", irun);
+    #endif
+                        its_write_obj(partial_mesh, fname);
+                    }
 #endif
                     its_merge(cummulative_mesh, partial_mesh);
                 }

src/libslic3r/TriangleMeshSlicer.cpp

@@ -62,6 +62,8 @@ public:
     // Inherits coord_t x, y
 };
 
+#define DEBUG_INTERSECTIONLINE (! defined(NDEBUG) || defined(SLIC3R_DEBUG_SLICE_PROCESSING))
+
 class IntersectionLine : public Line
 {
 public:
@@ -119,14 +121,14 @@ public:
     };
     uint32_t        flags { 0 };
 
-#ifndef NDEBUG
+#if DEBUG_INTERSECTIONLINE
     enum class Source {
         BottomPlane,
         TopPlane,
         Slab,
     };
     Source          source { Source::BottomPlane };
-#endif // NDEBUG
+#endif
 };
 
 using IntersectionLines = std::vector<IntersectionLine>;
@@ -1440,24 +1442,24 @@ static std::vector<Polygons> make_slab_loops(
                         for (const IntersectionLine &l : lines.at_slice[slice_below])
                             if (l.edge_type != IntersectionLine::FacetEdgeType::Top) {
                                 in.emplace_back(l);
-#ifndef NDEBUG
+#if DEBUG_INTERSECTIONLINE
                                 in.back().source = IntersectionLine::Source::BottomPlane;
-#endif // NDEBUG
+#endif // DEBUG_INTERSECTIONLINE
                             }
                     }
                     {
                         // Edges in between slice_below and slice_above.
-#ifndef NDEBUG
+#if DEBUG_INTERSECTIONLINE
                         size_t old_size = in.size();
-#endif // NDEBUG
+#endif // DEBUG_INTERSECTIONLINE
                         // Edge IDs of end points on in-between lines that touch the layer above are already increased with num_edges.
                         append(in, lines.between_slices[line_idx]);
-#ifndef NDEBUG
+#if DEBUG_INTERSECTIONLINE
                         for (auto it = in.begin() + old_size; it != in.end(); ++ it) {
                             assert(it->edge_type == IntersectionLine::FacetEdgeType::Slab);
                             it->source = IntersectionLine::Source::Slab;
                         }
-#endif // NDEBUG
+#endif // DEBUG_INTERSECTIONLINE
                     }
                     if (has_slice_above) {
                         for (const IntersectionLine &lsrc : lines.at_slice[slice_above])
@@ -1470,9 +1472,9 @@ static std::vector<Polygons> make_slab_loops(
                                     l.edge_a_id += num_edges;
                                 if (l.edge_b_id >= 0)
                                     l.edge_b_id += num_edges;
-#ifndef NDEBUG
+#if DEBUG_INTERSECTIONLINE
                                 l.source = IntersectionLine::Source::TopPlane;
-#endif // NDEBUG
+#endif // DEBUG_INTERSECTIONLINE
                             }
                     }
                     if (! in.empty()) {

src/libslic3r/libslic3r.h

@@ -124,8 +124,7 @@ inline void append(std::vector<T>& dest, std::vector<T>&& src)
         dest.insert(dest.end(),
             std::make_move_iterator(src.begin()),
             std::make_move_iterator(src.end()));
-
+        // Release memory of the source contour now.
-        // Vojta wants back compatibility
         src.clear();
         src.shrink_to_fit();
     }
@@ -161,8 +160,7 @@ inline void append_reversed(std::vector<T>& dest, std::vector<T>&& src)
         dest.insert(dest.end(), 
             std::make_move_iterator(src.rbegin()),
             std::make_move_iterator(src.rend()));
-
+    // Release memory of the source contour now.
-    // Vojta wants back compatibility
     src.clear();
     src.shrink_to_fit();
 }

t/shells.t

@@ -1,268 +0,0 @@
-use Test::More tests => 17;
-use strict;
-use warnings;
-
-BEGIN {
-    use FindBin;
-    use lib "$FindBin::Bin/../lib";
-    use local::lib "$FindBin::Bin/../local-lib";
-}
-
-use List::Util qw(first sum);
-use Slic3r;
-use Slic3r::Geometry qw(epsilon);
-use Slic3r::Test;
-
-# issue #1161
-{
-    my $config = Slic3r::Config::new_from_defaults;
-    $config->set('layer_height', 0.3);
-    $config->set('first_layer_height', $config->layer_height);
-    $config->set('bottom_solid_layers', 0);
-    $config->set('top_solid_layers', 3);
-    $config->set('cooling', [ 0 ]);
-    $config->set('bridge_speed', 99);
-    $config->set('solid_infill_speed', 99);
-    $config->set('top_solid_infill_speed', 99);
-    $config->set('first_layer_speed', '100%');
-    $config->set('enable_dynamic_overhang_speeds', 0);  # prevent speed alteration
-    
-    my $print = Slic3r::Test::init_print('V', config => $config);
-    my %layers_with_solid_infill = ();  # Z => 1
-    Slic3r::GCode::Reader->new->parse(Slic3r::Test::gcode($print), sub {
-        my ($self, $cmd, $args, $info) = @_;
-        
-        $layers_with_solid_infill{$self->Z} = 1
-            if $info->{extruding} && ($args->{F} // $self->F) == $config->solid_infill_speed*60;
-    });
-    is scalar(map $layers_with_solid_infill{$_}, grep $_ <= 7.2, keys %layers_with_solid_infill), 3,
-        "correct number of top solid shells is generated in V-shaped object";
-}
-
-{
-    my $config = Slic3r::Config::new_from_defaults;
-    # we need to check against one perimeter because this test is calibrated
-    # (shape, extrusion_width) so that perimeters cover the bottom surfaces of
-    # their lower layer - the test checks that shells are not generated on the
-    # above layers (thus 'across' the shadow perimeter)
-    # the test is actually calibrated to leave a narrow bottom region for each
-    # layer - we test that in case of fill_density = 0 such narrow shells are 
-    # discarded instead of grown
-    $config->set('perimeters', 1);
-    $config->set('fill_density', 0);
-    $config->set('cooling', [ 0 ]);             # prevent speed alteration
-    $config->set('first_layer_speed', '100%');  # prevent speed alteration
-    $config->set('enable_dynamic_overhang_speeds', 0);  # prevent speed alteration
-    $config->set('layer_height', 0.4);
-    $config->set('first_layer_height', $config->layer_height);
-    $config->set('extrusion_width', 0.55);
-    $config->set('bottom_solid_layers', 3);
-    $config->set('top_solid_layers', 0);
-    $config->set('solid_infill_speed', 99);
-    
-    my $print = Slic3r::Test::init_print('V', config => $config);
-    my %layers = ();  # Z => 1
-    Slic3r::GCode::Reader->new->parse(Slic3r::Test::gcode($print), sub {
-        my ($self, $cmd, $args, $info) = @_;
-        $layers{$self->Z} = 1
-            if $info->{extruding} && ($args->{F} // $self->F) == $config->solid_infill_speed*60;
-    });
-    is scalar(keys %layers), $config->bottom_solid_layers,
-        "shells are not propagated across perimeters of the neighbor layer";
-}
-
-{
-    my $config = Slic3r::Config::new_from_defaults;
-    $config->set('perimeters', 3);
-    $config->set('cooling', [ 0 ]);             # prevent speed alteration
-    $config->set('first_layer_speed', '100%');  # prevent speed alteration
-    $config->set('enable_dynamic_overhang_speeds', 0);  # prevent speed alteration
-    $config->set('layer_height', 0.4);
-    $config->set('first_layer_height', $config->layer_height);
-    $config->set('bottom_solid_layers', 3);
-    $config->set('top_solid_layers', 3);
-    $config->set('solid_infill_speed', 99);
-    $config->set('top_solid_infill_speed', 99);
-    $config->set('bridge_speed', 99);
-    $config->set('filament_diameter', [ 3.0 ]);
-    $config->set('nozzle_diameter', [ 0.5 ]);
-
-    my $print = Slic3r::Test::init_print('sloping_hole', config => $config);
-    my %solid_layers = ();  # Z => 1
-    Slic3r::GCode::Reader->new->parse(Slic3r::Test::gcode($print), sub {
-        my ($self, $cmd, $args, $info) = @_;
-        $solid_layers{$self->Z} = 1
-            if $info->{extruding} && ($args->{F} // $self->F) == $config->solid_infill_speed*60;
-    });
-    is scalar(keys %solid_layers), $config->bottom_solid_layers + $config->top_solid_layers,
-        "no superfluous shells are generated";
-}
-
-{
-    my $config = Slic3r::Config::new_from_defaults;
-    $config->set('perimeters', 1);
-    $config->set('fill_density', 0);
-    $config->set('top_solid_layers', 0);
-    $config->set('spiral_vase', 1);
-    $config->set('bottom_solid_layers', 0);
-    $config->set('skirts', 0);
-    $config->set('first_layer_height', $config->layer_height);
-    $config->set('start_gcode', '');
-    $config->set('temperature', [200]);
-    $config->set('first_layer_temperature', [205]);
-    
-    # TODO: this needs to be tested with a model with sloping edges, where starting
-    # points of each layer are not aligned - in that case we would test that no
-    # travel moves are left to move to the new starting point - in a cube, end
-    # points coincide with next layer starting points (provided there's no clipping)
-    my $test = sub {
-        my ($model_name, $description) = @_;
-        my $print = Slic3r::Test::init_print($model_name, config => $config);
-        my $travel_moves_after_first_extrusion = 0;
-        my $started_extruding = 0;
-        my $first_layer_temperature_set = 0;
-        my $temperature_set = 0;
-        my @z_steps = ();
-        Slic3r::GCode::Reader->new->parse(Slic3r::Test::gcode($print), sub {
-            my ($self, $cmd, $args, $info) = @_;
-            
-            if ($cmd eq 'G1') {
-                $started_extruding = 1 if $info->{extruding};
-                push @z_steps, $info->{dist_Z}
-                    if $started_extruding && $info->{dist_Z} > 0;
-                $travel_moves_after_first_extrusion++
-                    if $info->{travel} && $info->{dist_XY} > 0 && $started_extruding && !exists $args->{Z};
-            } elsif ($cmd eq 'M104') {
-                $first_layer_temperature_set = 1 if $args->{S} == 205;
-                $temperature_set = 1 if $args->{S} == 200;
-            }
-        });
-        
-        ok $first_layer_temperature_set, 'first layer temperature is preserved';
-        ok $temperature_set, 'temperature is preserved';
-        
-        # we allow one travel move after first extrusion: i.e. when moving to the first
-        # spiral point after moving to second layer (bottom layer had loop clipping, so
-        # we're slightly distant from the starting point of the loop)
-        ok $travel_moves_after_first_extrusion <= 1, "no gaps in spiral vase ($description)";
-        ok !(grep { $_ > $config->layer_height + epsilon } @z_steps), "no gaps in Z ($description)";
-    };
-    
-    $test->('20mm_cube', 'solid model');
-    
-    $config->set('z_offset', -10);
-    $test->('20mm_cube', 'solid model with negative z-offset');
-    
-    ### Disabled because the current unreliable medial axis code doesn't
-    ### always produce valid loops.
-    ###$test->('40x10', 'hollow model with negative z-offset');
-}
-
-{
-    my $config = Slic3r::Config::new_from_defaults;
-    $config->set('spiral_vase', 1);
-    $config->set('perimeters', 1);
-    $config->set('fill_density', 0);
-    $config->set('top_solid_layers', 0);
-    $config->set('bottom_solid_layers', 0);
-    $config->set('retract_layer_change', [0]);
-    $config->set('skirts', 0);
-    $config->set('layer_height', 0.4);
-    $config->set('first_layer_height', $config->layer_height);
-    $config->set('start_gcode', '');
-#    $config->set('use_relative_e_distances', 1);
-    $config->validate;
-    
-    my $print = Slic3r::Test::init_print('20mm_cube', config => $config);
-    my $z_moves = 0;
-    my @this_layer = ();  # [ dist_Z, dist_XY ], ...
-    
-    my $bottom_layer_not_flat = 0;
-    my $null_z_moves_not_layer_changes = 0;
-    my $null_z_moves_not_multiples_of_layer_height = 0;
-    my $sum_of_partial_z_equals_to_layer_height = 0;
-    my $all_layer_segments_have_same_slope = 0;
-    my $horizontal_extrusions = 0;
-    
-    Slic3r::GCode::Reader->new->parse(Slic3r::Test::gcode($print), sub {
-        my ($self, $cmd, $args, $info) = @_;
-        
-        if ($cmd eq 'G1') {
-            if ($z_moves < 2) {
-                # skip everything up to the second Z move
-                # (i.e. start of second layer)
-                if (exists $args->{Z}) {
-                    $z_moves++;
-                    $bottom_layer_not_flat = 1
-                        if $info->{dist_Z} > 0 && $info->{dist_Z} != $config->layer_height;
-                }
-            } elsif ($info->{dist_Z} == 0 && $args->{Z}) {
-                $null_z_moves_not_layer_changes = 1
-                    if $info->{dist_XY} != 0;
-                
-                # % doesn't work easily with floats
-                $null_z_moves_not_multiples_of_layer_height = 1
-                    if abs(($args->{Z} / $config->layer_height) * $config->layer_height - $args->{Z}) > epsilon;
-                
-                my $total_dist_XY = sum(map $_->[1], @this_layer);
-                $sum_of_partial_z_equals_to_layer_height = 1
-                    if abs(sum(map $_->[0], @this_layer) - $config->layer_height) > 
-                        # The first segment on the 2nd layer has extrusion interpolated from zero 
-                        # and the 1st segment has such a low extrusion assigned, that it is effectively zero, thus the move
-                        # is considered non-extruding and a higher epsilon is required.
-                        ($z_moves == 2 ? 0.0021 : epsilon);
-                #printf ("Total height: %f, layer height: %f, good: %d\n", sum(map $_->[0], @this_layer), $config->layer_height, $sum_of_partial_z_equals_to_layer_height);
-                
-                foreach my $segment (@this_layer) {
-                    # check that segment's dist_Z is proportioned to its dist_XY
-                    $all_layer_segments_have_same_slope = 1
-                        if abs($segment->[0]*$total_dist_XY/$config->layer_height - $segment->[1]) > 0.2;
-                }
-                
-                @this_layer = ();
-            } elsif ($info->{extruding} && $info->{dist_XY} > 0) {
-                $horizontal_extrusions = 1
-                    if $info->{dist_Z} == 0;
-                #printf("Pushing dist_z: %f, dist_xy: %f\n", $info->{dist_Z}, $info->{dist_XY});
-                push @this_layer, [ $info->{dist_Z}, $info->{dist_XY} ];
-            }
-        }
-    });
-    ok !$bottom_layer_not_flat, 'bottom layer is flat when using spiral vase';
-    ok !$null_z_moves_not_layer_changes, 'null Z moves are layer changes';
-    ok !$null_z_moves_not_multiples_of_layer_height, 'null Z moves are multiples of layer height';
-    ok !$sum_of_partial_z_equals_to_layer_height, 'sum of partial Z increments equals to a full layer height';
-    ok !$all_layer_segments_have_same_slope, 'all layer segments have the same slope';
-    ok !$horizontal_extrusions, 'no horizontal extrusions';
-}
-
-# The current Spiral Vase slicing code removes the holes and all but the largest contours from each slice,
-# therefore the following test is no more valid.
-#{
-#    my $config = Slic3r::Config::new_from_defaults;
-#    $config->set('perimeters', 1);
-#    $config->set('fill_density', 0);
-#    $config->set('top_solid_layers', 0);
-#    $config->set('spiral_vase', 1);
-#    $config->set('bottom_solid_layers', 0);
-#    $config->set('skirts', 0);
-#    $config->set('first_layer_height', $config->layer_height);
-#    $config->set('start_gcode', '');
-#    
-#    my $print = Slic3r::Test::init_print('two_hollow_squares', config => $config);
-#    my $diagonal_moves = 0;
-#    Slic3r::GCode::Reader->new->parse(Slic3r::Test::gcode($print), sub {
-#        my ($self, $cmd, $args, $info) = @_;
-#        
-#        if ($cmd eq 'G1') {
-#            if ($info->{extruding} && $info->{dist_XY} > 0) {
-#                if ($info->{dist_Z} > 0) {
-#                    $diagonal_moves++;
-#                }
-#            }
-#        }
-#    });
-#    is $diagonal_moves, 0, 'no spiral moves on two-island object';
-#}
-
-__END__

tests/fff_print/test_clipper.cpp

@@ -1,7 +1,7 @@
 #include <catch2/catch.hpp>
 
 #include "test_data.hpp"
-#include "clipper/clipper_z.hpp"
+#include "libslic3r/ClipperZUtils.hpp"
 #include "libslic3r/clipper.hpp"
 
 using namespace Slic3r;
@@ -132,3 +132,72 @@ SCENARIO("Clipper Z", "[ClipperZ]")
         REQUIRE(pt.z() == 1);
 }
 
+SCENARIO("Intersection with multiple polylines", "[ClipperZ]")
+{
+    // 1000x1000 CCQ square
+    ClipperLib_Z::Path clip { { 0, 0, 1 }, { 1000, 0, 1 }, { 1000, 1000, 1 }, { 0, 1000, 1 } };
+    // Two lines interseting inside the square above, crossing the bottom edge of the square.
+    ClipperLib_Z::Path line1 { { +100, -100, 2 }, { +900, +900, 2 } };
+    ClipperLib_Z::Path line2 { { +100, +900, 3 }, { +900, -100, 3 } };
+
+    ClipperLib_Z::Clipper clipper;
+    ClipperZUtils::ClipperZIntersectionVisitor::Intersections intersections;
+    ClipperZUtils::ClipperZIntersectionVisitor visitor(intersections);
+    clipper.ZFillFunction(visitor.clipper_callback());
+    clipper.AddPath(line1, ClipperLib_Z::ptSubject, false);
+    clipper.AddPath(line2, ClipperLib_Z::ptSubject, false);
+    clipper.AddPath(clip,  ClipperLib_Z::ptClip, true);
+
+    ClipperLib_Z::PolyTree polytree;
+    ClipperLib_Z::Paths    paths;
+    clipper.Execute(ClipperLib_Z::ctIntersection, polytree, ClipperLib_Z::pftNonZero, ClipperLib_Z::pftNonZero);
+    ClipperLib_Z::PolyTreeToPaths(polytree, paths);
+
+    REQUIRE(paths.size() == 2);
+
+    THEN("First output polyline is a trimmed 2nd line") {
+        // Intermediate point (intersection) was removed)
+        REQUIRE(paths.front().size() == 2);
+        REQUIRE(paths.front().front().z() == 3);
+        REQUIRE(paths.front().back().z() < 0);
+        REQUIRE(intersections[- paths.front().back().z() - 1] == std::pair<coord_t, coord_t>(1, 3));
+    }
+
+    THEN("Second output polyline is a trimmed 1st line") {
+        // Intermediate point (intersection) was removed)
+        REQUIRE(paths[1].size() == 2);
+        REQUIRE(paths[1].front().z() < 0);
+        REQUIRE(paths[1].back().z() == 2);
+        REQUIRE(intersections[- paths[1].front().z() - 1] == std::pair<coord_t, coord_t>(1, 2));
+    }
+}
+
+SCENARIO("Interseting a closed loop as an open polyline", "[ClipperZ]")
+{
+    // 1000x1000 CCQ square
+    ClipperLib_Z::Path clip{ { 0, 0, 1 }, { 1000, 0, 1 }, { 1000, 1000, 1 }, { 0, 1000, 1 } };
+    // Two lines interseting inside the square above, crossing the bottom edge of the square.
+    ClipperLib_Z::Path rect{ { 500, 500, 2}, { 500, 1500, 2 }, { 1500, 1500, 2}, { 500, 1500, 2}, { 500, 500, 2 } };
+
+    ClipperLib_Z::Clipper clipper;
+    clipper.AddPath(rect, ClipperLib_Z::ptSubject, false);
+    clipper.AddPath(clip, ClipperLib_Z::ptClip, true);
+
+    ClipperLib_Z::PolyTree polytree;
+    ClipperLib_Z::Paths    paths;
+    ClipperZUtils::ClipperZIntersectionVisitor::Intersections intersections;
+    ClipperZUtils::ClipperZIntersectionVisitor visitor(intersections);
+    clipper.ZFillFunction(visitor.clipper_callback());
+    clipper.Execute(ClipperLib_Z::ctIntersection, polytree, ClipperLib_Z::pftNonZero, ClipperLib_Z::pftNonZero);
+    ClipperLib_Z::PolyTreeToPaths(std::move(polytree), paths);
+
+    THEN("Open polyline is clipped into two pieces") {
+        REQUIRE(paths.size() == 2);
+        REQUIRE(paths.front().size() == 2);
+        REQUIRE(paths.back().size() == 2);
+        REQUIRE(paths.front().front().z() == 2);
+        REQUIRE(paths.back().back().z() == 2);
+        REQUIRE(paths.front().front().x() == paths.back().back().x());
+        REQUIRE(paths.front().front().y() == paths.back().back().y());
+    }
+}

tests/fff_print/test_shells.cpp

@@ -9,16 +9,14 @@ using namespace Slic3r;
 
 SCENARIO("Shells", "[Shells]") {
     GIVEN("20mm box") {
-        auto test = [](const DynamicPrintConfig &config){
+        auto test = [](const DynamicPrintConfig &config){            
-            std::string gcode = Slic3r::Test::slice({ Slic3r::Test::TestMesh::cube_20x20x20 }, config);
-            
             std::vector<coord_t> zs;
             std::set<coord_t> layers_with_solid_infill;
             std::set<coord_t> layers_with_bridge_infill;
             const double solid_infill_speed = config.opt_float("solid_infill_speed") * 60;
             const double bridge_speed       = config.opt_float("bridge_speed") * 60;
             GCodeReader parser;
-            parser.parse_buffer(gcode,
+            parser.parse_buffer(Slic3r::Test::slice({ Slic3r::Test::TestMesh::cube_20x20x20 }, config),
                 [&zs, &layers_with_solid_infill, &layers_with_bridge_infill, solid_infill_speed, bridge_speed]
                     (Slic3r::GCodeReader &self, const Slic3r::GCodeReader::GCodeLine &line)
             {
@@ -110,3 +108,294 @@ SCENARIO("Shells", "[Shells]") {
         }
     }
 }
+
+static std::set<double> layers_with_speed(const std::string &gcode, int speed)
+{
+    std::set<double> out;
+    GCodeReader parser;
+    parser.parse_buffer(gcode, [&out, speed](Slic3r::GCodeReader &self, const Slic3r::GCodeReader::GCodeLine &line) {
+        if (line.extruding(self) && is_approx<double>(line.new_F(self), speed * 60.))
+            out.insert(self.z());
+    });
+    return out;
+}
+
+SCENARIO("Shells (from Perl)", "[Shells]") {
+    GIVEN("V shape, Slic3r GH #1161") {
+        int solid_speed = 99;
+        auto config = Slic3r::DynamicPrintConfig::full_print_config_with({
+            { "layer_height",           0.3 },
+            { "first_layer_height",     0.3 },
+            { "bottom_solid_layers",    0 },
+            { "top_solid_layers",       3 },
+            // to prevent speeds from being altered
+            { "cooling",                "0" },
+            { "bridge_speed",           solid_speed },
+            { "solid_infill_speed",     solid_speed },
+            { "top_solid_infill_speed", solid_speed },
+            // to prevent speeds from being altered
+            { "first_layer_speed",      "100%" },
+            // prevent speed alteration
+            { "enable_dynamic_overhang_speeds", 0 }
+        });
+        
+        THEN("correct number of top solid shells is generated in V-shaped object") {
+            size_t n = 0;
+            for (auto z : layers_with_speed(Slic3r::Test::slice({TestMesh::V}, config), solid_speed))
+                if (z <= 7.2)
+                    ++ n;
+            REQUIRE(n == 3);
+        }
+    }
+    GIVEN("V shape") {
+        // we need to check against one perimeter because this test is calibrated
+        // (shape, extrusion_width) so that perimeters cover the bottom surfaces of
+        // their lower layer - the test checks that shells are not generated on the
+        // above layers (thus 'across' the shadow perimeter)
+        // the test is actually calibrated to leave a narrow bottom region for each
+        // layer - we test that in case of fill_density = 0 such narrow shells are 
+        // discarded instead of grown
+        int bottom_solid_layers = 3;
+        auto config = Slic3r::DynamicPrintConfig::full_print_config_with({
+            { "perimeters",             1 },
+            { "fill_density",           0 },
+            // to prevent speeds from being altered
+            { "cooling",                "0" },
+            // to prevent speeds from being altered
+            { "first_layer_speed",      "100%" },
+            // prevent speed alteration
+            { "enable_dynamic_overhang_speeds", 0 },
+            { "layer_height",           0.4 },
+            { "first_layer_height",     0.4 },
+            { "extrusion_width",        0.55 },
+            { "bottom_solid_layers",    bottom_solid_layers },
+            { "top_solid_layers",       0 },
+            { "solid_infill_speed",     99 }
+        });
+        THEN("shells are not propagated across perimeters of the neighbor layer") {
+            std::string gcode = Slic3r::Test::slice({TestMesh::V}, config);
+            REQUIRE(layers_with_speed(gcode, 99).size() == bottom_solid_layers);
+        }
+    }
+    GIVEN("sloping_hole") {
+        int bottom_solid_layers = 3;
+        int top_solid_layers    = 3;
+        int solid_speed         = 99;
+        auto config = Slic3r::DynamicPrintConfig::full_print_config_with({
+            { "perimeters",             3 },
+            // to prevent speeds from being altered
+            { "cooling",                "0" },
+            // to prevent speeds from being altered
+            { "first_layer_speed",      "100%" },
+            // prevent speed alteration
+            { "enable_dynamic_overhang_speeds", 0 },
+            { "layer_height",           0.4 },
+            { "first_layer_height",     0.4 },
+            { "bottom_solid_layers",    bottom_solid_layers },
+            { "top_solid_layers",       top_solid_layers },
+            { "solid_infill_speed",     solid_speed },
+            { "top_solid_infill_speed", solid_speed },
+            { "bridge_speed",           solid_speed },
+            { "filament_diameter",      3. },
+            { "nozzle_diameter",        0.5 }
+        });
+        THEN("no superfluous shells are generated") {
+            std::string gcode = Slic3r::Test::slice({TestMesh::sloping_hole}, config);
+            REQUIRE(layers_with_speed(gcode, solid_speed).size() == bottom_solid_layers + top_solid_layers);
+        }
+    }
+    GIVEN("20mm_cube, spiral vase") {
+        double layer_height = 0.3;
+        auto config = Slic3r::DynamicPrintConfig::full_print_config_with({
+            { "perimeters",             1 },
+            { "fill_density",           0 },
+            { "layer_height",           layer_height },
+            { "first_layer_height",     layer_height },
+            { "top_solid_layers",       0 },
+            { "spiral_vase",            1 },
+            { "bottom_solid_layers",    0 },
+            { "skirts",                 0 },
+            { "start_gcode",            "" },
+            { "temperature",            200 },
+            { "first_layer_temperature", 205}
+        });
+        
+        // TODO: this needs to be tested with a model with sloping edges, where starting
+        // points of each layer are not aligned - in that case we would test that no
+        // travel moves are left to move to the new starting point - in a cube, end
+        // points coincide with next layer starting points (provided there's no clipping)
+        auto test = [layer_height](const DynamicPrintConfig &config) {
+            size_t              travel_moves_after_first_extrusion  = 0;
+            bool                started_extruding                   = false;
+            bool                first_layer_temperature_set         = false;
+            bool                temperature_set                     = false;
+            std::vector<double> z_steps;
+            GCodeReader         parser;
+            parser.parse_buffer(Slic3r::Test::slice({TestMesh::cube_20x20x20}, config), 
+                [&](Slic3r::GCodeReader &self, const Slic3r::GCodeReader::GCodeLine &line) {
+                if (line.cmd_is("G1")) {
+                    if (line.extruding(self))
+                        started_extruding = true;
+                    if (started_extruding) {
+                        if (double dz = line.dist_Z(self); dz > 0)
+                            z_steps.emplace_back(dz);
+                        if (line.travel() && line.dist_XY(self) > 0 && ! line.has(Z))
+                            ++ travel_moves_after_first_extrusion;
+                    }
+                } else if (line.cmd_is("M104")) {
+                    int s;
+                    if (line.has_value('S', s)) {
+                        if (s == 205)
+                            first_layer_temperature_set = true;
+                        else if (s == 200)
+                            temperature_set = true;
+                    }
+                }
+            });
+            THEN("first layer temperature is set") {
+                REQUIRE(first_layer_temperature_set);
+            }
+            THEN("temperature is set") {
+                REQUIRE(temperature_set);
+            }
+            // we allow one travel move after first extrusion: i.e. when moving to the first
+            // spiral point after moving to second layer (bottom layer had loop clipping, so
+            // we're slightly distant from the starting point of the loop)
+            THEN("no gaps in spiral vase") {
+                REQUIRE(travel_moves_after_first_extrusion <= 1);
+            }
+            THEN("no gaps in Z") {
+                REQUIRE(std::count_if(z_steps.begin(), z_steps.end(), 
+                    [&layer_height](auto z_step) { return z_step > layer_height + EPSILON; }) == 0);
+            }
+        };
+        WHEN("solid model") {
+            test(config);
+        }
+        WHEN("solid model with negative z-offset") {
+            config.set_deserialize_strict("z_offset", "-10");
+            test(config);
+        }
+        // Disabled because the current unreliable medial axis code doesn't always produce valid loops.
+        // $test->('40x10', 'hollow model with negative z-offset');
+    }
+    GIVEN("20mm_cube, spiral vase") {
+        double layer_height = 0.4;
+        auto config = Slic3r::DynamicPrintConfig::full_print_config_with({
+            { "spiral_vase",            1 },
+            { "perimeters",             1 },
+            { "fill_density",           0 },
+            { "top_solid_layers",       0 },
+            { "bottom_solid_layers",    0 },
+            { "retract_layer_change",   0 },
+            { "skirts",                 0 },
+            { "layer_height",           layer_height },
+            { "first_layer_height",     layer_height },
+            { "start_gcode",            "" },
+            // { "use_relative_e_distances", 1}
+        });
+        config.validate();
+        
+        std::vector<std::pair<double, double>> this_layer; // [ dist_Z, dist_XY ], ...
+        int  z_moves                                    = 0;
+        bool bottom_layer_not_flat                      = false;
+        bool null_z_moves_not_layer_changes             = false;
+        bool null_z_moves_not_multiples_of_layer_height = false;
+        bool sum_of_partial_z_equals_to_layer_height    = false;
+        bool all_layer_segments_have_same_slope         = false;
+        bool horizontal_extrusions                      = false;
+        GCodeReader parser;
+        parser.parse_buffer(Slic3r::Test::slice({TestMesh::cube_20x20x20}, config), 
+            [&](Slic3r::GCodeReader &self, const Slic3r::GCodeReader::GCodeLine &line) {
+            if (line.cmd_is("G1")) {
+                if (z_moves < 2) {
+                    // skip everything up to the second Z move
+                    // (i.e. start of second layer)
+                    if (line.has(Z)) {
+                        ++ z_moves;
+                        if (double dz = line.dist_Z(self); dz > 0 && ! is_approx<double>(dz, layer_height))
+                            bottom_layer_not_flat = true;
+                    }
+                } else if (line.dist_Z(self) == 0 && line.has(Z)) {
+                    if (line.dist_XY(self) != 0)
+                        null_z_moves_not_layer_changes = true;
+                    double z = line.new_Z(self);
+                    if (fmod(z + EPSILON, layer_height) > 2 * EPSILON)
+                        null_z_moves_not_multiples_of_layer_height = true;
+                    double total_dist_XY = 0;
+                    double total_dist_Z  = 0;
+                    for (auto &seg : this_layer) {
+                        total_dist_Z  += seg.first;
+                        total_dist_XY += seg.second;
+                    }
+                    if (std::abs(total_dist_Z - layer_height) >
+                            // The first segment on the 2nd layer has extrusion interpolated from zero 
+                            // and the 1st segment has such a low extrusion assigned, that it is effectively zero, thus the move
+                            // is considered non-extruding and a higher epsilon is required.
+                            (z_moves == 2 ? 0.0021 : EPSILON))
+                        sum_of_partial_z_equals_to_layer_height = true;
+                    //printf("Total height: %f, layer height: %f, good: %d\n", sum(map $_->[0], @this_layer), $config->layer_height, $sum_of_partial_z_equals_to_layer_height);
+                    for (auto &seg : this_layer)
+                        // check that segment's dist_Z is proportioned to its dist_XY
+                        if (std::abs(seg.first * total_dist_XY / layer_height - seg.second) > 0.2)
+                            all_layer_segments_have_same_slope = true;
+                    this_layer.clear();
+                } else if (line.extruding(self) && line.dist_XY(self) > 0) {
+                    if (line.dist_Z(self) == 0)
+                        horizontal_extrusions = true;
+                    //printf("Pushing dist_z: %f, dist_xy: %f\n", $info->{dist_Z}, $info->{dist_XY});
+                    this_layer.emplace_back(line.dist_Z(self), line.dist_XY(self));
+                }
+            }
+        });
+        THEN("bottom layer is flat when using spiral vase") {
+            REQUIRE(! bottom_layer_not_flat);
+        }
+        THEN("null Z moves are layer changes") {
+            REQUIRE(! null_z_moves_not_layer_changes);
+        }
+        THEN("null Z moves are multiples of layer height") {
+            REQUIRE(! null_z_moves_not_multiples_of_layer_height);
+        }
+        THEN("sum of partial Z increments equals to a full layer height") {
+            REQUIRE(! sum_of_partial_z_equals_to_layer_height);
+        }
+        THEN("all layer segments have the same slope") {
+            REQUIRE(! all_layer_segments_have_same_slope);
+        }
+        THEN("no horizontal extrusions") {
+            REQUIRE(! horizontal_extrusions);
+        }
+    }
+}
+
+#if 0
+// The current Spiral Vase slicing code removes the holes and all but the largest contours from each slice,
+// therefore the following test is no more valid.
+{
+    my $config = Slic3r::Config::new_from_defaults;
+    $config->set('perimeters', 1);
+    $config->set('fill_density', 0);
+    $config->set('top_solid_layers', 0);
+    $config->set('spiral_vase', 1);
+    $config->set('bottom_solid_layers', 0);
+    $config->set('skirts', 0);
+    $config->set('first_layer_height', $config->layer_height);
+    $config->set('start_gcode', '');
+    
+    my $print = Slic3r::Test::init_print('two_hollow_squares', config => $config);
+    my $diagonal_moves = 0;
+    Slic3r::GCode::Reader->new->parse(Slic3r::Test::gcode($print), sub {
+        my ($self, $cmd, $args, $info) = @_;
+        
+        if ($cmd eq 'G1') {
+            if ($info->{extruding} && $info->{dist_XY} > 0) {
+                if ($info->{dist_Z} > 0) {
+                    $diagonal_moves++;
+                }
+            }
+        }
+    });
+    is $diagonal_moves, 0, 'no spiral moves on two-island object';
+}
+#endif

tests/libslic3r/CMakeLists.txt

@@ -23,6 +23,7 @@ add_executable(${_TEST_NAME}_tests
 	test_stl.cpp
 	test_meshboolean.cpp
 	test_marchingsquares.cpp
+	test_region_expansion.cpp
 	test_timeutils.cpp
 	test_utils.cpp
 	test_voronoi.cpp

tests/libslic3r/test_placeholder_parser.cpp

@@ -31,6 +31,7 @@ SCENARIO("Placeholder parser scripting", "[PlaceholderParser]") {
 	parser.set("foo", 0);
 	parser.set("bar", 2);
 	parser.set("num_extruders", 4);
+    parser.set("gcode_flavor", "marlin");
 
     SECTION("nested config options (legacy syntax)") { REQUIRE(parser.process("[temperature_[foo]]") == "357"); }
     SECTION("array reference") { REQUIRE(parser.process("{temperature[foo]}") == "357"); }
@@ -115,4 +116,5 @@ SCENARIO("Placeholder parser scripting", "[PlaceholderParser]") {
     SECTION("complex expression") { REQUIRE(boolean_expression("printer_notes=~/.*PRINTER_VENDOR_PRUSA3D.*/ and printer_notes=~/.*PRINTER_MODEL_MK2.*/ and nozzle_diameter[0]==0.6 and num_extruders>1")); }
     SECTION("complex expression2") { REQUIRE(boolean_expression("printer_notes=~/.*PRINTER_VEwerfNDOR_PRUSA3D.*/ or printer_notes=~/.*PRINTertER_MODEL_MK2.*/ or (nozzle_diameter[0]==0.6 and num_extruders>1)")); }
     SECTION("complex expression3") { REQUIRE(! boolean_expression("printer_notes=~/.*PRINTER_VEwerfNDOR_PRUSA3D.*/ or printer_notes=~/.*PRINTertER_MODEL_MK2.*/ or (nozzle_diameter[0]==0.3 and num_extruders>1)")); }
+    SECTION("enum expression") { REQUIRE(boolean_expression("gcode_flavor == \"marlin\"")); }
 }

tests/libslic3r/test_polygon.cpp

@@ -196,19 +196,6 @@ SCENARIO("Simplify polygon", "[Polygon]")
             }
         }
     }
-    GIVEN("hole in square") {
-        // CW oriented
-        auto hole_in_square = Polygon{ {140, 140}, {140, 160}, {160, 160}, {160, 140} };
-        WHEN("simplified") {
-            Polygons simplified = hole_in_square.simplify(2.);
-            THEN("hole simplification returns one polygon") {
-                REQUIRE(simplified.size() == 1);
-            }
-            THEN("hole simplification turns cw polygon into ccw polygon") {
-                REQUIRE(simplified.front().is_counter_clockwise());
-            }
-        }
-    }
 }
 
 #include "libslic3r/ExPolygon.hpp"

tests/libslic3r/test_region_expansion.cpp

@@ -0,0 +1,284 @@
+#include <catch2/catch.hpp>
+
+#include <libslic3r/libslic3r.h>
+#include <libslic3r/Algorithm/RegionExpansion.hpp>
+#include <libslic3r/ClipperUtils.hpp>
+#include <libslic3r/ExPolygon.hpp>
+#include <libslic3r/Polygon.hpp>
+#include <libslic3r/SVG.cpp>
+
+using namespace Slic3r;
+
+//#define DEBUG_TEMP_DIR "d:\\temp\\"
+
+SCENARIO("Region expansion basics", "[RegionExpansion]") {
+    static constexpr const coord_t ten = scaled<coord_t>(10.);
+    GIVEN("two touching squares") {
+        Polygon square1{ { 1 * ten, 1 * ten }, { 2 * ten, 1 * ten }, { 2 * ten, 2 * ten }, { 1 * ten, 2 * ten } };
+        Polygon square2{ { 2 * ten, 1 * ten }, { 3 * ten, 1 * ten }, { 3 * ten, 2 * ten }, { 2 * ten, 2 * ten } };
+        Polygon square3{ { 1 * ten, 2 * ten }, { 2 * ten, 2 * ten }, { 2 * ten, 3 * ten }, { 1 * ten, 3 * ten } };
+        static constexpr const float expansion = scaled<float>(1.);
+        auto test_expansion = [](const Polygon &src, const Polygon &boundary) {
+            std::vector<Polygons> expanded = Algorithm::expand_expolygons({ ExPolygon{src} }, { ExPolygon{boundary} },
+                expansion,
+                scaled<float>(0.3), // expansion step
+                5);                 // max num steps
+            THEN("Single anchor is produced") {
+                REQUIRE(expanded.size() == 1);
+            }
+            THEN("The area of the anchor is 10mm2") {
+                REQUIRE(area(expanded.front()) == Approx(expansion * ten));
+            }
+        };
+
+        WHEN("second square expanded into the first square (to left)") {
+            test_expansion(square2, square1);
+        }
+        WHEN("first square expanded into the second square (to right)") {
+            test_expansion(square1, square2);
+        }
+        WHEN("third square expanded into the first square (down)") {
+            test_expansion(square3, square1);
+        }
+        WHEN("first square expanded into the third square (up)") {
+            test_expansion(square1, square3);
+        }
+    }
+
+    GIVEN("simple bridge") {
+        Polygon square1{ { 1 * ten, 1 * ten }, { 2 * ten, 1 * ten }, { 2 * ten, 2 * ten }, { 1 * ten, 2 * ten } };
+        Polygon square2{ { 2 * ten, 1 * ten }, { 3 * ten, 1 * ten }, { 3 * ten, 2 * ten }, { 2 * ten, 2 * ten } };
+        Polygon square3{ { 3 * ten, 1 * ten }, { 4 * ten, 1 * ten }, { 4 * ten, 2 * ten }, { 3 * ten, 2 * ten } };
+
+        WHEN("expanded") {
+            static constexpr const float expansion = scaled<float>(1.);
+            std::vector<Polygons> expanded = Algorithm::expand_expolygons({ ExPolygon{square2} }, { ExPolygon{square1}, ExPolygon{square3} },
+                expansion,
+                scaled<float>(0.3), // expansion step
+                5);                 // max num steps
+            THEN("Two anchors are produced") {
+                REQUIRE(expanded.size() == 1);
+                REQUIRE(expanded.front().size() == 2);
+            }
+            THEN("The area of each anchor is 10mm2") {
+                REQUIRE(area(expanded.front().front()) == Approx(expansion * ten));
+                REQUIRE(area(expanded.front().back()) == Approx(expansion * ten));
+            }
+        }
+
+        WHEN("fully expanded") {
+            static constexpr const float expansion = scaled<float>(10.1);
+            std::vector<Polygons> expanded = Algorithm::expand_expolygons({ ExPolygon{square2} }, { ExPolygon{square1}, ExPolygon{square3} },
+                expansion,
+                scaled<float>(2.3), // expansion step
+                5);                 // max num steps
+            THEN("Two anchors are produced") {
+                REQUIRE(expanded.size() == 1);
+                REQUIRE(expanded.front().size() == 2);
+            }
+            THEN("The area of each anchor is 100mm2") {
+                REQUIRE(area(expanded.front().front()) == Approx(sqr<double>(ten)));
+                REQUIRE(area(expanded.front().back()) == Approx(sqr<double>(ten)));
+            }
+        }
+    }
+
+    GIVEN("two bridges") {
+        Polygon left_support  { { 1 * ten, 1 * ten }, { 2 * ten, 1 * ten }, { 2 * ten, 4 * ten }, { 1 * ten, 4 * ten } };
+        Polygon right_support { { 3 * ten, 1 * ten }, { 4 * ten, 1 * ten }, { 4 * ten, 4 * ten }, { 3 * ten, 4 * ten } };
+        Polygon bottom_bridge { { 2 * ten, 1 * ten }, { 3 * ten, 1 * ten }, { 3 * ten, 2 * ten }, { 2 * ten, 2 * ten } };
+        Polygon top_bridge    { { 2 * ten, 3 * ten }, { 3 * ten, 3 * ten }, { 3 * ten, 4 * ten }, { 2 * ten, 4 * ten } };
+
+        WHEN("expanded") {
+            static constexpr const float expansion = scaled<float>(1.);
+            std::vector<Polygons> expanded = Algorithm::expand_expolygons({ ExPolygon{bottom_bridge}, ExPolygon{top_bridge} }, { ExPolygon{left_support}, ExPolygon{right_support} },
+                expansion,
+                scaled<float>(0.3), // expansion step
+                5);                 // max num steps
+#if 0
+            SVG::export_expolygons(DEBUG_TEMP_DIR "two_bridges-out.svg",
+                { { { { ExPolygon{left_support}, ExPolygon{right_support} } }, { "supports", "orange", 0.5f } },
+                  { { { ExPolygon{bottom_bridge}, ExPolygon{top_bridge} } },   { "bridges",  "blue",   0.5f } },
+                  { { union_ex(union_(expanded.front(), expanded.back())) },   { "expanded", "red",    "black", "", scaled<coord_t>(0.1f), 0.5f } } });
+#endif
+            THEN("Two anchors are produced for each bridge") {
+                REQUIRE(expanded.size() == 2);
+                REQUIRE(expanded.front().size() == 2);
+                REQUIRE(expanded.back().size() == 2);
+            }
+            THEN("The area of each anchor is 10mm2") {
+                double a = expansion * ten + M_PI * sqr(expansion) / 4;
+                double eps = sqr(scaled<double>(0.1));
+                REQUIRE(is_approx(area(expanded.front().front()), a, eps));
+                REQUIRE(is_approx(area(expanded.front().back()), a, eps));
+                REQUIRE(is_approx(area(expanded.back().front()), a, eps));
+                REQUIRE(is_approx(area(expanded.back().back()), a, eps));
+            }
+        }
+    }
+
+    GIVEN("rectangle with rhombic cut-out") {
+        double  diag = 1 * ten * sqrt(2.) / 4.;
+        Polygon square_with_rhombic_cutout{ { 0, 0 }, { 1 * ten, 0 }, { ten / 2, ten / 2 }, { 1 * ten, 1 * ten }, { 0, 1 * ten } };
+        Polygon rhombic { { ten / 2, ten / 2 }, { 3 * ten / 4, ten / 4 }, { 1 * ten, ten / 2 }, { 3 * ten / 4, 3 * ten / 4 } };
+
+        WHEN("expanded") {
+            static constexpr const float expansion = scaled<float>(1.);
+            std::vector<Polygons> expanded = Algorithm::expand_expolygons({ ExPolygon{rhombic} }, { ExPolygon{square_with_rhombic_cutout} },
+                expansion,
+                scaled<float>(0.1), // expansion step
+                11);                // max num steps
+#if 0
+            SVG::export_expolygons(DEBUG_TEMP_DIR "rectangle_with_rhombic_cut-out.svg",
+                { { { { ExPolygon{square_with_rhombic_cutout} } }, { "square_with_rhombic_cutout", "orange", 0.5f } },
+                  { { { ExPolygon{rhombic} } },                    { "rhombic",                    "blue",   0.5f } },
+                  { { union_ex(expanded.front()) },                { "bridges",                    "red",    "black", "", scaled<coord_t>(0.1f), 0.5f } } });
+#endif
+            THEN("Single anchor is produced") {
+                REQUIRE(expanded.size() == 1);
+            }
+            THEN("The area of anchor is correct") {
+                double area_calculated = area(expanded.front());
+                double area_expected = 2. * diag * expansion + M_PI * sqr(expansion) * 0.75;
+                REQUIRE(is_approx(area_expected, area_calculated, sqr(scaled<double>(0.2))));
+            }
+        }
+
+        WHEN("extra expanded") {
+            static constexpr const float expansion = scaled<float>(2.5);
+            std::vector<Polygons> expanded = Algorithm::expand_expolygons({ ExPolygon{rhombic} }, { ExPolygon{square_with_rhombic_cutout} },
+                expansion,
+                scaled<float>(0.25), // expansion step
+                11);                 // max num steps
+#if 0
+            SVG::export_expolygons(DEBUG_TEMP_DIR "rectangle_with_rhombic_cut-out2.svg",
+                { { { { ExPolygon{square_with_rhombic_cutout} } }, { "square_with_rhombic_cutout", "orange", 0.5f } },
+                  { { { ExPolygon{rhombic} } },                    { "rhombic",                    "blue",   0.5f } },
+                  { { union_ex(expanded.front()) },                { "bridges",                    "red",    "black", "", scaled<coord_t>(0.1f), 0.5f } } });
+#endif
+            THEN("Single anchor is produced") {
+                REQUIRE(expanded.size() == 1);
+            }
+            THEN("The area of anchor is correct") {
+                double area_calculated = area(expanded.front());
+                double area_expected = 2. * diag * expansion + M_PI * sqr(expansion) * 0.75;
+                REQUIRE(is_approx(area_expected, area_calculated, sqr(scaled<double>(0.3))));
+            }
+        }
+    }
+
+    GIVEN("square with two holes") {
+        Polygon outer{ { 0, 0 }, { 3 * ten, 0 }, { 3 * ten, 5 * ten }, { 0, 5 * ten } };
+        Polygon hole1{ { 1 * ten, 1 * ten }, { 1 * ten, 2 * ten }, { 2 * ten, 2 * ten }, { 2 * ten, 1 * ten } };
+        Polygon hole2{ { 1 * ten, 3 * ten }, { 1 * ten, 4 * ten }, { 2 * ten, 4 * ten }, { 2 * ten, 3 * ten } };
+        ExPolygon boundary(outer);
+        boundary.holes = { hole1, hole2 };
+
+        Polygon anchor{ { -1 * ten, coord_t(1.5 * ten) }, { 0 * ten, coord_t(1.5 * ten) }, { 0, coord_t(3.5 * ten) }, { -1 * ten, coord_t(3.5 * ten) } };
+
+        WHEN("expanded") {
+            static constexpr const float expansion = scaled<float>(5.);
+            std::vector<Polygons> expanded = Algorithm::expand_expolygons({ ExPolygon{anchor} }, { boundary },
+                expansion,
+                scaled<float>(0.4), // expansion step
+                15);                // max num steps
+#if 0
+            SVG::export_expolygons(DEBUG_TEMP_DIR "square_with_two_holes-out.svg",
+                { { { { ExPolygon{anchor} } }, { "anchor", "orange", 0.5f } },
+                  { { { boundary } },          { "boundary",  "blue", 0.5f } },
+                  { { union_ex(expanded.front()) }, { "expanded", "red", "black", "", scaled<coord_t>(0.1f), 0.5f } } });
+#endif
+            THEN("The anchor expands into a single region") {
+                REQUIRE(expanded.size() == 1);
+                REQUIRE(expanded.front().size() == 1);
+            }
+            THEN("The area of anchor is correct") {
+                double area_calculated = area(expanded.front());
+                double area_expected = double(expansion) * 2. * double(ten) + M_PI * sqr(expansion) * 0.5;
+                REQUIRE(is_approx(area_expected, area_calculated, sqr(scaled<double>(0.45))));
+            }
+        }
+        WHEN("expanded even more") {
+            static constexpr const float expansion = scaled<float>(25.);
+            std::vector<Polygons> expanded = Algorithm::expand_expolygons({ ExPolygon{anchor} }, { boundary },
+                expansion,
+                scaled<float>(2.), // expansion step
+                15);               // max num steps
+#if 0
+            SVG::export_expolygons(DEBUG_TEMP_DIR "square_with_two_holes-expanded2-out.svg",
+                { { { { ExPolygon{anchor} } }, { "anchor", "orange", 0.5f } },
+                  { { { boundary } },          { "boundary",  "blue", 0.5f } },
+                  { { union_ex(expanded.front()) }, { "expanded", "red", "black", "", scaled<coord_t>(0.1f), 0.5f } } });
+#endif
+            THEN("The anchor expands into a single region") {
+                REQUIRE(expanded.size() == 1);
+                REQUIRE(expanded.front().size() == 1);
+            }
+        }
+        WHEN("expanded yet even more") {
+            static constexpr const float expansion = scaled<float>(28.);
+            std::vector<Polygons> expanded = Algorithm::expand_expolygons({ ExPolygon{anchor} }, { boundary },
+                expansion,
+                scaled<float>(2.), // expansion step
+                20);               // max num steps
+#if 0
+            SVG::export_expolygons(DEBUG_TEMP_DIR "square_with_two_holes-expanded3-out.svg",
+                { { { { ExPolygon{anchor} } }, { "anchor", "orange", 0.5f } },
+                  { { { boundary } },          { "boundary",  "blue", 0.5f } },
+                  { { union_ex(expanded.front()) }, { "expanded", "red", "black", "", scaled<coord_t>(0.1f), 0.5f } } });
+#endif
+            THEN("The anchor expands into a single region with two holes") {
+                REQUIRE(expanded.size() == 1);
+                REQUIRE(expanded.front().size() == 3);
+            }
+        }
+        WHEN("expanded fully") {
+            static constexpr const float expansion = scaled<float>(35.);
+            std::vector<Polygons> expanded = Algorithm::expand_expolygons({ ExPolygon{anchor} }, { boundary },
+                expansion,
+                scaled<float>(2.), // expansion step
+                25);               // max num steps
+#if 0
+            SVG::export_expolygons(DEBUG_TEMP_DIR "square_with_two_holes-expanded_fully-out.svg",
+                { { { { ExPolygon{anchor} } }, { "anchor", "orange", 0.5f } },
+                  { { { boundary } },          { "boundary",  "blue", 0.5f } },
+                  { { union_ex(expanded.front()) }, { "expanded", "red", "black", "", scaled<coord_t>(0.1f), 0.5f } } });
+#endif
+            THEN("The anchor expands into a single region with two holes, fully covering the boundary") {
+                REQUIRE(expanded.size() == 1);
+                REQUIRE(expanded.front().size() == 3);
+                REQUIRE(area(expanded.front()) == Approx(area(boundary)));
+            }
+        }
+    }
+    GIVEN("square with hole, hole edge anchored") {
+        Polygon outer{ { -1 * ten, -1 * ten }, { 2 * ten, -1 * ten }, { 2 * ten, 2 * ten }, { -1 * ten, 2 * ten } };
+        Polygon hole { { 0, ten }, { ten, ten }, { ten, 0 }, { 0, 0 } };
+        Polygon anchor{ { 0, 0 }, { ten, 0 }, { ten, ten }, { 0, ten } };
+        ExPolygon boundary(outer);
+        boundary.holes = { hole };
+
+        WHEN("expanded") {
+            static constexpr const float expansion = scaled<float>(5.);
+            std::vector<Polygons> expanded = Algorithm::expand_expolygons({ ExPolygon{anchor} }, { boundary },
+                expansion,
+                scaled<float>(0.4), // expansion step
+                15);                // max num steps
+#if 0
+            SVG::export_expolygons(DEBUG_TEMP_DIR "square_with_hole_anchored-out.svg",
+                { { { { ExPolygon{anchor} } }, { "anchor", "orange", 0.5f } },
+                  { { { boundary } },          { "boundary", "blue", 0.5f } },
+                  { { union_ex(expanded.front()) }, { "expanded", "red", "black", "", scaled<coord_t>(0.1f), 0.5f } } });
+#endif
+            THEN("The anchor expands into a single region with a hole") {
+                REQUIRE(expanded.size() == 1);
+                REQUIRE(expanded.front().size() == 2);
+            }
+            THEN("The area of anchor is correct") {
+                double area_calculated = area(expanded.front());
+                double area_expected = double(expansion) * 4. * double(ten) + M_PI * sqr(expansion);
+                REQUIRE(is_approx(area_expected, area_calculated, sqr(scaled<double>(0.6))));
+            }
+        }
+    }
+}