Minor improvement to drawing offset.

tests/testapp.py

@@ -76,7 +76,8 @@ class Polygon(BoundingBoxArea):
             cr.stroke()
 
         # Fill polygon
-        cr.translate(self.x, self.y)
+        rx, ry = self.get_root_offset()
+        cr.translate(rx, ry)
         cr.new_path()
 
         for x, y in zip(*self.points):