onViewportResize method
Override in order to perform a custom action upon resize.
A typical use-case would be to adjust the viewport's clip mask to match the new size.
Implementation
@override
void onViewportResize() {
final x = size.x / 2;
final y = size.y / 2;
_clipPath = Path()..addOval(Rect.fromLTRB(-x, -y, x, y));
}