diff method
返回终点与始点的差距
Implementation
Offset? diff() {
if (scaleUpdateDetails != null && scaleStartDetails != null) {
final dx = scaleUpdateDetails!.localFocalPoint.dx -
scaleStartDetails!.localFocalPoint.dx;
final dy = scaleUpdateDetails!.localFocalPoint.dy -
scaleStartDetails!.localFocalPoint.dy;
return Offset(dx, dy);
}
return null;
}