Ported Polygon->area

xs/src/Polygon.cpp

@@ -54,6 +54,14 @@ Polygon::split_at_first_point()
     return this->split_at_index(0);
 }
 
+double
+Polygon::area()
+{
+    ClipperLib::Polygon p;
+    Slic3rPolygon_to_ClipperPolygon(*this, p);
+    return ClipperLib::Area(p);
+}
+
 bool
 Polygon::is_counter_clockwise()
 {

xs/src/Polygon.hpp

@@ -16,6 +16,7 @@ class Polygon : public MultiPoint {
     Polyline* split_at(const Point* point);
     Polyline* split_at_index(int index);
     Polyline* split_at_first_point();
+    double area();
     bool is_counter_clockwise();
     bool make_counter_clockwise();
     bool make_clockwise();