Bugfix: prevent crashes from rounding issues caused by almost-collinear points in the new FillRectilinear. #3684

xs/src/libslic3r/ExPolygon.cpp

@@ -129,6 +129,14 @@ ExPolygon::has_boundary_point(const Point &point) const
     return false;
 }
 
+void
+ExPolygon::remove_vertical_collinear_points(coord_t tolerance)
+{
+    this->contour.remove_vertical_collinear_points(tolerance);
+    for (Polygon &p : this->holes)
+        p.remove_vertical_collinear_points(tolerance);
+}
+
 void
 ExPolygon::simplify_p(double tolerance, Polygons* polygons) const
 {

xs/src/libslic3r/ExPolygon.hpp

@@ -29,6 +29,7 @@ class ExPolygon
     bool contains(const Point &point) const;
     bool contains_b(const Point &point) const;
     bool has_boundary_point(const Point &point) const;
+    void remove_vertical_collinear_points(coord_t tolerance);
     void simplify_p(double tolerance, Polygons* polygons) const;
     Polygons simplify_p(double tolerance) const;
     ExPolygons simplify(double tolerance) const;

xs/src/libslic3r/Fill/FillRectilinear.cpp

@@ -1,3 +1,9 @@
+//#define DEBUG_RECTILINEAR
+#ifdef DEBUG_RECTILINEAR
+    #undef NDEBUG
+    #include "../SVG.hpp"
+#endif
+
 #include "../ClipperUtils.hpp"
 #include "../ExPolygon.hpp"
 #include "../PolylineCollection.hpp"
@@ -7,17 +13,16 @@
 
 #include "FillRectilinear.hpp"
 
-//#define DEBUG_RECTILINEAR
-#ifdef DEBUG_RECTILINEAR
-    #include "../SVG.hpp"
-#endif
-
 namespace Slic3r {
 
 void
 FillRectilinear::_fill_single_direction(ExPolygon expolygon,
     const direction_t &direction, coord_t x_shift, Polylines* out)
 {
+    // Remove almost collinear points (vertical ones might break this algorithm
+    // because of rounding).
+    expolygon.remove_vertical_collinear_points(1);
+    
     // rotate polygons so that we can work with vertical lines here
     expolygon.rotate(-direction.first);
     

xs/src/libslic3r/Polygon.cpp

@@ -148,6 +148,32 @@ Polygon::contains(const Point &point) const
     return result;
 }
 
+void
+Polygon::douglas_peucker(double tolerance)
+{
+    this->points.push_back(this->points.front());
+    this->points = MultiPoint::_douglas_peucker(this->points, tolerance);
+    this->points.pop_back();
+}
+
+void
+Polygon::remove_vertical_collinear_points(coord_t tolerance)
+{
+    Points &pp = this->points;
+    pp.push_back(pp.front());
+    for (size_t i = 0; i < pp.size()-1; ++i) {
+        while (i < pp.size()-1) {
+            Point &next = pp[i+1];
+            if (std::abs(next.x - pp[i].x) <= tolerance) {
+                pp.erase(pp.begin() + i+1);
+            } else {
+                break;
+            }
+        }
+    }
+    pp.pop_back();
+}
+
 // this only works on CCW polygons as CW will be ripped out by Clipper's simplify_polygons()
 Polygons
 Polygon::simplify(double tolerance) const

xs/src/libslic3r/Polygon.hpp

@@ -39,6 +39,8 @@ class Polygon : public MultiPoint {
     // Does an unoriented polygon contain a point?
     // Tested by counting intersections along a horizontal line.
     bool contains(const Point &point) const;
+    void douglas_peucker(double tolerance);
+    void remove_vertical_collinear_points(coord_t tolerance);
     Polygons simplify(double tolerance) const;
     void simplify(double tolerance, Polygons &polygons) const;
     void triangulate_convex(Polygons* polygons) const;