Resizing the window could leave artifacts from the previous frame on
the canvas that is not overwritten by the self.canvas.copy(...) call.
Former-commit-id: c5479c3e9346a25f2d5e7a7f7b8198a71d16e16a
Former-commit-id: a2cc07de426ed1eca5437e30f4a15278065d856c