Added a new Slic3r::Geometry::simplify_polygons() function

xs/src/libslic3r/ExPolygon.cpp

@@ -129,14 +129,20 @@ ExPolygon::simplify_p(double tolerance) const
     pp.reserve(this->holes.size() + 1);
     
     // contour
+    {
         Polygon p = this->contour;
+        p.points.push_back(p.points.front());
         p.points = MultiPoint::_douglas_peucker(p.points, tolerance);
+        p.points.pop_back();
         pp.push_back(p);
+    }
     
     // holes
     for (Polygons::const_iterator it = this->holes.begin(); it != this->holes.end(); ++it) {
-        p = *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);
     }
     simplify_polygons(pp, &pp);

xs/src/libslic3r/Geometry.cpp

@@ -1,4 +1,5 @@
 #include "Geometry.hpp"
+#include "ClipperUtils.hpp"
 #include "ExPolygon.hpp"
 #include "Line.hpp"
 #include "PolylineCollection.hpp"
@@ -146,6 +147,20 @@ deg2rad(double angle)
     return PI * angle / 180.0;
 }
 
+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);
+    }
+    Slic3r::simplify_polygons(pp, retval);
+}
+
 Line
 MedialAxis::edge_to_line(const VD::edge_type &edge) const
 {

xs/src/libslic3r/Geometry.hpp

@@ -21,6 +21,7 @@ template<class T> bool contains(const std::vector<T> &vector, const Point &point
 double rad2deg(double angle);
 double rad2deg_dir(double angle);
 double deg2rad(double angle);
+void simplify_polygons(const Polygons &polygons, double tolerance, Polygons* retval);
 
 class MedialAxis {
     public:

xs/src/libslic3r/Polygon.cpp

@@ -147,6 +147,7 @@ Polygon::contains(const Point &point) const
     return result;
 }
 
+// this only works on CCW polygons as CW will be ripped out by Clipper's simplify_polygons()
 Polygons
 Polygon::simplify(double tolerance) const
 {

xs/xsp/Geometry.xsp

@@ -78,4 +78,13 @@ deg2rad(angle)
     OUTPUT:
         RETVAL
 
+Polygons
+simplify_polygons(polygons, tolerance)
+    Polygons    polygons
+    double      tolerance
+    CODE:
+        Slic3r::Geometry::simplify_polygons(polygons, tolerance, &RETVAL);
+    OUTPUT:
+        RETVAL
+
 %}