paint method
Draw itself and its children, according to the calculated
box.offset
Implementation
@override
void paint(Context context) {
super.paint(context);
if (child == null) {
return;
}
final box = _getBox(context);
final mat = Matrix4.tryInvert(context.canvas.getTransform())!;
mat.translate(box.x, box.y);
context.canvas
..saveContext()
..setTransform(mat);
child!.paint(context);
context.canvas.restoreContext();
}