Fixed faulty drawing offset.

tests/testapp.py

@@ -102,7 +102,7 @@ class Polygon(BoundingBoxArea):
             cr.stroke()
 
         # Fill polygon
-        rx, ry = self.get_root_offset()
+        rx, ry = self.get_offset(root)
         cr.translate(rx, ry)
         cr.new_path()