Question

I have an issue getting the X and Y values from mutlitouch events. Below is the code showing how I get the value when the POINTER_DOWN and POINTER_UP events are fired, however the X and Y values seem to get mixed up / duplicated on the POINTER_UP event.

@Override
public void onTouchEvent(MotionEvent event) {

int id, pointerIndex;

switch (event.getAction() & MotionEvent.ACTION_MASK) {

  case MotionEvent.ACTION_POINTER_DOWN:

    pointerIndex = (event.getAction() & MotionEvent.ACTION_POINTER_ID_MASK) 
    >> MotionEvent.ACTION_POINTER_ID_SHIFT;
    id = event.getPointerId(pointerIndex);

    Log.e("Down", ""+id+" "+event.getX(id)+" "+event.getY(id));

    break;

case MotionEvent.ACTION_POINTER_UP:

    pointerIndex = (event.getAction() & MotionEvent.ACTION_POINTER_ID_MASK) 
    >> MotionEvent.ACTION_POINTER_ID_SHIFT;
    id = event.getPointerId(pointerIndex);

    Log.e("UP", ""+id+" "+event.getX(id)+" "+event.getY(id));

    break;
}

super.onTouchEvent(event);

}

This typically results in the following lolcat:

E/DOWN    (25070): 0 279.60922 279.17447
E/DOWN    (25070): 1 513.20044 520.3252
E/DOWN    (25070): 2 422.6651 358.72418

E/UP      (25070): 0 279.60922 279.17447
E/UP      (25070): 1 422.6651 358.72418 
E/UP      (25070): 2 422.6651 358.72418 

Here you can see that the XY location for id 1 is wrong, showing instead the values id 2.

Note that no ACTION_CANCEL events are called. I imagine it’s something wrong with my use of the MASKS/ANDing. Any help would be much appreciated!

Answer 1

Apparently event.getX and event.getY should be fed the pointer index, not the pointer id.