Android Multitouch events using MotionEvent

 ACTION_POINTER_DOWN and ACTION_POINTER_UP are fired whenever a secondary pointer goes down or up.

• If there is already a pointer on the screen and a new one goes down, you will receive ACTION_POINTER_DOWN instead of ACTION_DOWN. Subsequent pointers will fire  ACTION_POINTER_DOWN too and to get the actual pointer ID us with ACTION_POINTER_INDEX_MASK. 
• If a pointer goes up but there is still at least one touching the screen, you will receive ACTION_POINTER_UP instead of ACTION_UP.
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