Little refactoring of douglas_peucker()

src/libslic3r/ExPolygon.cpp

@@ -184,14 +184,14 @@ Polygons ExPolygon::simplify_p(double tolerance) const
     {
         Polygon p = this->contour;
         p.points.push_back(p.points.front());
-        p.points = MultiPoint::_douglas_peucker(p.points, tolerance);
+        p.points = MultiPoint::douglas_peucker(p.points, tolerance);
         p.points.pop_back();
         pp.emplace_back(std::move(p));
     }
     // holes
     for (Polygon p : this->holes) {
         p.points.push_back(p.points.front());
-        p.points = MultiPoint::_douglas_peucker(p.points, tolerance);
+        p.points = MultiPoint::douglas_peucker(p.points, tolerance);
         p.points.pop_back();
         pp.emplace_back(std::move(p));
     }

src/libslic3r/Geometry.cpp

@@ -52,15 +52,15 @@ template bool contains(const ExPolygons &vector, const Point &point);
 
 void simplify_polygons(const Polygons &polygons, double tolerance, Polygons* retval)
 {
-    Polygons pp;
-    for (Polygons::const_iterator it = polygons.begin(); it != polygons.end(); ++it) {
-        Polygon p = *it;
-        p.points.push_back(p.points.front());
-        p.points = MultiPoint::_douglas_peucker(p.points, tolerance);
-        p.points.pop_back();
-        pp.push_back(p);
+    Polygons simplified_raw;
+    for (const Polygon &source_polygon : polygons) {
+        Points simplified = MultiPoint::douglas_peucker(to_polyline(source_polygon).points, tolerance);
+        if (simplified.size() > 3) {
+            simplified.pop_back();
+            simplified_raw.push_back(Polygon{ std::move(simplified) });
+        }
     }
-    *retval = Slic3r::simplify_polygons(pp);
+    *retval = Slic3r::simplify_polygons(simplified_raw);
 }
 
 double linint(double value, double oldmin, double oldmax, double newmin, double newmax)

src/libslic3r/MultiPoint.cpp

@@ -103,7 +103,7 @@ bool MultiPoint::remove_duplicate_points()
     return false;
 }
 
-Points MultiPoint::_douglas_peucker(const Points &pts, const double tolerance)
+Points MultiPoint::douglas_peucker(const Points &pts, const double tolerance)
 {
     Points result_pts;
 	double tolerance_sq = tolerance * tolerance;

src/libslic3r/MultiPoint.hpp

@@ -81,7 +81,7 @@ public:
         }
     }
 
-    static Points _douglas_peucker(const Points &points, const double tolerance);
+    static Points douglas_peucker(const Points &points, const double tolerance);
     static Points visivalingam(const Points& pts, const double& tolerance);
 
     inline auto begin()        { return points.begin(); }

src/libslic3r/Polygon.cpp

@@ -96,7 +96,7 @@ bool Polygon::make_clockwise()
 void Polygon::douglas_peucker(double tolerance)
 {
     this->points.push_back(this->points.front());
-    Points p = MultiPoint::_douglas_peucker(this->points, tolerance);
+    Points p = MultiPoint::douglas_peucker(this->points, tolerance);
     p.pop_back();
     this->points = std::move(p);
 }
@@ -110,7 +110,7 @@ Polygons Polygon::simplify(double tolerance) const
     // on the whole polygon
     Points points = this->points;
     points.push_back(points.front());
-    Polygon p(MultiPoint::_douglas_peucker(points, tolerance));
+    Polygon p(MultiPoint::douglas_peucker(points, tolerance));
     p.points.pop_back();
     
     Polygons pp;
@@ -577,23 +577,40 @@ void remove_collinear(Polygons &polys)
 		remove_collinear(poly);
 }
 
-Polygons polygons_simplify(const Polygons &source_polygons, double tolerance)
+static inline void simplify_polygon_impl(const Points &points, double tolerance, bool strictly_simple, Polygons &out)
+{
+    Points simplified = MultiPoint::douglas_peucker(points, tolerance);
+    // then remove the last (repeated) point.
+    simplified.pop_back();
+    // Simplify the decimated contour by ClipperLib.
+    bool ccw = ClipperLib::Area(simplified) > 0.;
+    for (Points& path : ClipperLib::SimplifyPolygons(ClipperUtils::SinglePathProvider(simplified), ClipperLib::pftNonZero, strictly_simple)) {
+        if (!ccw)
+            // ClipperLib likely reoriented negative area contours to become positive. Reverse holes back to CW.
+            std::reverse(path.begin(), path.end());
+        out.emplace_back(std::move(path));
+    }
+}
+
+Polygons polygons_simplify(Polygons &&source_polygons, double tolerance, bool strictly_simple /* = true */)
+{
+    Polygons out;
+    out.reserve(source_polygons.size());
+    for (Polygon &source_polygon : source_polygons) {
+        // Run Douglas / Peucker simplification algorithm on an open polyline (by repeating the first point at the end of the polyline),
+        source_polygon.points.emplace_back(source_polygon.points.front());
+        simplify_polygon_impl(source_polygon.points, tolerance, strictly_simple, out);
+    }
+    return out;
+}
+
+Polygons polygons_simplify(const Polygons &source_polygons, double tolerance, bool strictly_simple /* = true */)
 {
     Polygons out;
     out.reserve(source_polygons.size());
     for (const Polygon &source_polygon : source_polygons) {
         // Run Douglas / Peucker simplification algorithm on an open polyline (by repeating the first point at the end of the polyline),
-        Points simplified = MultiPoint::_douglas_peucker(to_polyline(source_polygon).points, tolerance);
-        // then remove the last (repeated) point.
-        simplified.pop_back();
-        // Simplify the decimated contour by ClipperLib.
-        bool ccw = ClipperLib::Area(simplified) > 0.;
-        for (Points &path : ClipperLib::SimplifyPolygons(ClipperUtils::SinglePathProvider(simplified), ClipperLib::pftNonZero)) {
-            if (! ccw)
-                // ClipperLib likely reoriented negative area contours to become positive. Reverse holes back to CW.
-                std::reverse(path.begin(), path.end());
-            out.emplace_back(std::move(path));
-        }
+        simplify_polygon_impl(to_polyline(source_polygon).points, tolerance, strictly_simple, out);
     }
     return out;
 }

src/libslic3r/Polygon.hpp

@@ -149,7 +149,8 @@ inline void polygons_append(Polygons &dst, Polygons &&src)
     }
 }
 
-Polygons polygons_simplify(const Polygons &polys, double tolerance);
+Polygons polygons_simplify(Polygons &&polys, double tolerance, bool strictly_simple = true);
+Polygons polygons_simplify(const Polygons &polys, double tolerance, bool strictly_simple = true);
 
 inline void polygons_rotate(Polygons &polys, double angle)
 {

src/libslic3r/Polyline.cpp

@@ -110,7 +110,7 @@ Points Polyline::equally_spaced_points(double distance) const
 
 void Polyline::simplify(double tolerance)
 {
-    this->points = MultiPoint::_douglas_peucker(this->points, tolerance);
+    this->points = MultiPoint::douglas_peucker(this->points, tolerance);
 }
 
 #if 0