handleDownEvent method
Implementation
void handleDownEvent(PointerDownEvent event) {
if (null == _old1 && _old2?.device != event.device) {
_old1 = Pointer(device: event.device, dx: event.position.dx, dy: event.position.dy);
} else if (null == _old2 && _old1!.device != event.device) {
_old2 = Pointer(device: event.device, dx: event.position.dx, dy: event.position.dy);
}
}