addVisualOverflow method
Implementation
void addVisualOverflow(Rect rect) {
assert(_visualOverflowRect != null, 'add overflow rect failed, _visualOverflowRect not init');
_visualOverflowRect = Rect.fromLTWH(
min(_visualOverflowRect!.left, rect.left),
min(_visualOverflowRect!.top, rect.top),
max(_visualOverflowRect!.right, rect.right),
max(_visualOverflowRect!.bottom, rect.bottom));
}