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Question by VGP117 · Sep 06, 2015 at 01:55 PM · uimobiletouchdrag-and-drop

Drag UI by touch

The Scrollrect works horribly with multitouch so I want to do my own solution.

I got this code from unity learn-page:

 public void OnPointerDown (PointerEventData data) {
         RectTransformUtility.ScreenPointToLocalPointInRectangle (panelRectTransform, data.position, data.pressEventCamera, out pointerOffset);
         pointerOffset = pointerOffset * panelRectTransform.localScale.x;
     }
 
     public void OnDrag (PointerEventData data) {
         if (panelRectTransform == null)
             return;
 
         Vector2 localPointerPosition;
         if (RectTransformUtility.ScreenPointToLocalPointInRectangle (
             canvasRectTransform, data.position, data.pressEventCamera, out localPointerPosition
             )) {
             panelRectTransform.localPosition = localPointerPosition - pointerOffset;
         }
     }
 

I got it almost working by replacing data.position with Input.GetTouch(0).position, but the pointerOffset is always wrong because setting any camera instead of data.pressEventCamera doesn't work.

So the question is what can I put into the RectTransformUtility instead of data.pressEventCamera?

Thanks for answering!

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Answer by Avelorn · Sep 13, 2015 at 07:45 PM

@VGP117 Steal the camera? :) In other words take the camera in the callback method of your choice. Camera c = data.pressEventCamera and then just use that.

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Answer by VGP117 · Sep 14, 2015 at 09:31 AM

Thanks for the answer. But I've already done my own solution for RectTransformUtility.ScreenPointToLocalPointInRectangle too.

For anyone wondering here is my new code:

 public void OnPointerDown (PointerEventData data) 
     {
         mouseOffset = GetPointerOffSet (panelRectTransform, data.position);
     }
     
     public void OnDrag (PointerEventData data) 
     {
         panelRectTransform.localPosition = GetCenteredPointerPos (data.position) - mouseOffset;
     }
 
 Vector2 GetPointerOffSet (RectTransform rt, Vector2 pointerPos) 
     {
         Vector2 centeredPointerPos = (GetCenteredPointerPos (pointerPos));
         Vector2 offSet = centeredPointerPos - (Vector2)rt.localPosition;
         return offSet;
 
     }
 
     Vector2 GetCenteredPointerPos (Vector2 pointerPos) 
     {
         Vector2 centeredPointerPos = new Vector2 (pointerPos.x - Screen.width / 2f, pointerPos.y - Screen.height / 2f);
         centeredPointerPos /= canvasRectTransform.localScale.x;
         return centeredPointerPos;
     }


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