so first you have to register some code from the onPointerMove, up and down:
PointerEventTypes.POINTERDOWN | PointerEventTypes.POINTERUP |
myCode will be called for all the associated events.
You can check the code used by the arcrotatecamera here:
Specifically on pointer up herE:
The overall idea is to track evt.PointerId to identify multiple touch points and then evaluate distance between point A and B to detect the pinch