Android multi-touch. How exactly does it work-android

Android multi-touch. How exactly does it work

OK Guys, I was wondering if someone would be kind enough to explain exactly how multi-touch works in Android? I've read various blogs and tuts online (including the official developers guide) but I still can't make head nor tails of it.

If I press the screen with one finger, no problem, I also know how to detect a non-primary finger touching the screen.

But if I have say, 2 fingers on the screen and I remove one of them, how can I determine where the remaining finger is on the screen? This is partly what I don't understand.

Where does event.getPointerCount, event.getActionIndex(); & event.getActionMasked(); come into it?

Here is my code: Please see the MotionEvent.ACTION_POINTER_UP: section, this is the part I don't understand - I need to know where the remaining fingers are.

Would be grateful for any help - thanks!!

Code

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Note: Text content in the code blocks is automatically word-wrapped
@Override
        public boolean onTouchEvent(MotionEvent event) {

         int actionMask = event.getActionMasked();
        int pointerIndex = event.getActionIndex();
        int pointerCount = event.getPointerCount();

            switch (actionMask){

            case MotionEvent.ACTION_DOWN:

                        //If primary finger presses left button, move sprite left
                if (event.getX()<=renderer.leftButton("right") && event.getY()>=renderer.leftButton("top")){
                        renderer.setSpriteState('l', true);
                        renderer.setSpriteState('r', false);
                    }