From 5db91f1944ff2def24a9e548b25024873f211f4c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Luk=C3=A1=C5=A1=20Hejl?= <hejl.lukas@gmail.com>
Date: Wed, 23 Mar 2022 11:49:26 +0100
Subject: [PATCH] Added detection for a missing Voronoi vertex. If the missing
 Voronoi vertex is detected, try to resolve it by rotation input polygons.

---
 .../Arachne/SkeletalTrapezoidation.cpp        | 89 ++++++++++++++++++-
 1 file changed, 87 insertions(+), 2 deletions(-)

diff --git a/src/libslic3r/Arachne/SkeletalTrapezoidation.cpp b/src/libslic3r/Arachne/SkeletalTrapezoidation.cpp
index fabdc2486f..c07dafd542 100644
--- a/src/libslic3r/Arachne/SkeletalTrapezoidation.cpp
+++ b/src/libslic3r/Arachne/SkeletalTrapezoidation.cpp
@@ -378,6 +378,52 @@ SkeletalTrapezoidation::SkeletalTrapezoidation(const Polygons& polys, const Bead
     constructFromPolygons(polys);
 }
 
+bool detect_missing_voronoi_vertex(const Geometry::VoronoiDiagram &voronoi_diagram, const std::vector<SkeletalTrapezoidation::Segment> &segments) {
+    for (VoronoiUtils::vd_t::cell_type cell : voronoi_diagram.cells()) {
+        if (!cell.incident_edge())
+            continue; // There is no spoon
+
+        if (cell.contains_segment()) {
+            const SkeletalTrapezoidation::Segment &source_segment = VoronoiUtils::getSourceSegment(cell, segments);
+            const Point                            from           = source_segment.from();
+            const Point                            to             = source_segment.to();
+
+            // Find starting edge
+            // Find end edge
+            bool                           seen_possible_start             = false;
+            bool                           after_start                     = false;
+            bool                           ending_edge_is_set_before_start = false;
+            VoronoiUtils::vd_t::edge_type *starting_vd_edge                = nullptr;
+            VoronoiUtils::vd_t::edge_type *ending_vd_edge                  = nullptr;
+            VoronoiUtils::vd_t::edge_type *edge                            = cell.incident_edge();
+            do {
+                if (edge->is_infinite()) continue;
+
+                Vec2i64 v0 = VoronoiUtils::p(edge->vertex0());
+                Vec2i64 v1 = VoronoiUtils::p(edge->vertex1());
+
+                assert(!(v0 == to.cast<int64_t>() && v1 == from.cast<int64_t>()));
+                if (v0 == to.cast<int64_t>() && !after_start) { // Use the last edge which starts in source_segment.to
+                    starting_vd_edge    = edge;
+                    seen_possible_start = true;
+                } else if (seen_possible_start) {
+                    after_start = true;
+                }
+
+                if (v1 == from.cast<int64_t>() && (!ending_vd_edge || ending_edge_is_set_before_start)) {
+                    ending_edge_is_set_before_start = !after_start;
+                    ending_vd_edge                  = edge;
+                }
+            } while (edge = edge->next(), edge != cell.incident_edge());
+
+            if (!starting_vd_edge || !ending_vd_edge || starting_vd_edge == ending_vd_edge)
+                return true;
+        }
+    }
+
+    return false;
+}
+
 void SkeletalTrapezoidation::constructFromPolygons(const Polygons& polys)
 {
     // Check self intersections.
@@ -399,8 +445,37 @@ void SkeletalTrapezoidation::constructFromPolygons(const Polygons& polys)
     Geometry::VoronoiDiagram voronoi_diagram;
     construct_voronoi(segments.begin(), segments.end(), &voronoi_diagram);
 
-    for (vd_t::cell_type cell : voronoi_diagram.cells())
-    {
+    // Try to detect cases when some Voronoi vertex is missing.
+    // When any Voronoi vertex is missing, rotate input polygon and try again.
+    const bool                                  has_missing_voronoi_vertex = detect_missing_voronoi_vertex(voronoi_diagram, segments);
+    const double                                fix_angle                  = PI / 6;
+    std::unordered_map<Point, Point, PointHash> vertex_mapping;
+    Polygons                                    polys_copy = polys;
+    if (has_missing_voronoi_vertex) {
+        BOOST_LOG_TRIVIAL(debug) << "Detected missing Voronoi vertex, input polygons will be rotated back and forth.";
+        for (Polygon &poly : polys_copy)
+            poly.rotate(fix_angle);
+
+        assert(polys_copy.size() == polys.size());
+        for (size_t poly_idx = 0; poly_idx < polys.size(); ++poly_idx) {
+            assert(polys_copy[poly_idx].size() == polys[poly_idx].size());
+            for (size_t point_idx = 0; point_idx < polys[poly_idx].size(); ++point_idx)
+                vertex_mapping.insert({polys[poly_idx][point_idx], polys_copy[poly_idx][point_idx]});
+        }
+
+        segments.clear();
+        for (size_t poly_idx = 0; poly_idx < polys_copy.size(); poly_idx++)
+            for (size_t point_idx = 0; point_idx < polys_copy[poly_idx].size(); point_idx++)
+                segments.emplace_back(&polys_copy, poly_idx, point_idx);
+
+        voronoi_diagram.clear();
+        construct_voronoi(segments.begin(), segments.end(), &voronoi_diagram);
+        assert(!detect_missing_voronoi_vertex(voronoi_diagram, segments));
+        if (detect_missing_voronoi_vertex(voronoi_diagram, segments))
+            BOOST_LOG_TRIVIAL(error) << "Detected missing Voronoi vertex even after the rotation of input.";
+    }
+
+    for (vd_t::cell_type cell : voronoi_diagram.cells()) {
         if (!cell.incident_edge())
             continue; // There is no spoon
 
@@ -455,6 +530,16 @@ void SkeletalTrapezoidation::constructFromPolygons(const Polygons& polys)
         prev_edge->to->data.distance_to_boundary = 0;
     }
 
+    if (has_missing_voronoi_vertex) {
+        for (node_t &node : graph.nodes) {
+            // If a mapping exists between a rotated point and an original point, use this mapping. Otherwise, rotate a point in the opposite direction.
+            if (auto node_it = vertex_mapping.find(node.p); node_it != vertex_mapping.end())
+                node.p = node_it->second;
+            else
+                node.p.rotate(-fix_angle);
+        }
+    }
+
     separatePointyQuadEndNodes();
 
     graph.fixNodeDuplication();