New ExPolygon::triangulate() method

xs/src/ExPolygon.cpp

@@ -176,6 +176,18 @@ ExPolygon::get_trapezoids(Polygons* polygons, double angle) const
         polygon->rotate(-(PI/2 - angle), Point(0,0));
 }
 
+void
+ExPolygon::triangulate(Polygons* polygons) const
+{
+    // first make trapezoids
+    Polygons trapezoids;
+    this->get_trapezoids(&trapezoids);
+    
+    // then triangulate each trapezoid
+    for (Polygons::iterator polygon = trapezoids.begin(); polygon != trapezoids.end(); ++polygon)
+        polygon->triangulate_convex(polygons);
+}
+
 #ifdef SLIC3RXS
 SV*
 ExPolygon::to_AV() {

xs/src/ExPolygon.hpp

@@ -29,6 +29,7 @@ class ExPolygon
     void medial_axis(double max_width, double min_width, Polylines* polylines) const;
     void get_trapezoids(Polygons* polygons) const;
     void get_trapezoids(Polygons* polygons, double angle) const;
+    void triangulate(Polygons* polygons) const;
     
     #ifdef SLIC3RXS
     void from_SV(SV* poly_sv);

xs/src/Polygon.cpp

@@ -168,7 +168,9 @@ Polygon::triangulate_convex(Polygons* polygons) const
         p.points.push_back(this->points.front());
         p.points.push_back(*(it-1));
         p.points.push_back(*it);
-        polygons->push_back(p);
+        
+        // this should be replaced with a more efficient call to a merge_collinear_segments() method
+        if (p.area() > 0) polygons->push_back(p);
     }
 }
 

xs/t/04_expolygon.t

@@ -3,9 +3,9 @@
 use strict;
 use warnings;
 
-use List::Util qw(first);
+use List::Util qw(first sum);
 use Slic3r::XS;
-use Test::More tests => 31;
+use Test::More tests => 33;
 
 use constant PI => 4 * atan2(1, 1);
 
@@ -133,4 +133,10 @@ is $expolygon->area, 100*100-20*20, 'area';
     is scalar(grep { $_->area == 100*200 } @$polygons), 1, 'trapezoids have expected area';
 }
 
+{
+    my $triangles = $expolygon->triangulate;
+    is scalar(@$triangles), 8, 'expected number of triangles';
+    is sum(map $_->area, @$triangles), $expolygon->area, 'sum of triangles area equals original expolygon area';
+}
+
 __END__

xs/xsp/ExPolygon.xsp

@@ -31,6 +31,8 @@
         %code{% THIS->medial_axis(max_width, min_width, &RETVAL); %};
     Polygons get_trapezoids(double angle)
         %code{% THIS->get_trapezoids(&RETVAL, angle); %};
+    Polygons triangulate()
+        %code{% THIS->triangulate(&RETVAL); %};
 %{
 
 ExPolygon*