Understanding MotionEvent to implement a virtual DPad and Buttons on Android (Multitouch)

Question

I'm trying to implement a virtual DPad in android, but I'm still very confused about how do I keep track of each trouch point, from the moment it is pressed, till it is released.

In my code, I test if there is a "DOWN" or "MOVED" event, then if one of this events collides with one of the 4 rectangles of my DPad, I set the pressedDirectin variable to the side of the DPad which the user pressed.

The thing I'm not sure, is how do I get track of the touch points, I want to store the ID of the touch point which collided with the DPad direction, so when this ID is moved I update the direction of the DPad and when it gets released I set the Direction to None.

I don't want my DPad to handle multiple directions, but I still didn't get how to handle the multiple touch points, so I can know exacly which touch point is touching the DPad and store it's ID so I know when it is released.

Is the onTouchEvent called for every touch point, or all touch points comes in a single call? I still don't get it.

Here is the code I wrote so far, it works, but guess that it will only handle one touch point.

public boolean onTouchEvent(MotionEvent event)
    {
        if (event.getPointerCount() == 0) 
            return true;

        int touchX = -1;
        int touchY = -1;

        pressedDirection = DPadDirection.None;
        int actionCode = event.getAction() & MotionEvent.ACTION_MASK;
            if (actionCode == MotionEvent.ACTION_UP)
            {
                if (event.getPointerId(0) == idDPad)
                {
                    pressedDirection = DPadDirection.None;
                    idDPad = -1;
                }
            }
            else if (actionCode == MotionEvent.ACTION_DOWN || actionCode == MotionEvent.ACTION_MOVE)
            {                                     
                touchX = (int)event.getX();
                touchY = (int)event.getY();     

                if (rightRect.contains(touchX, touchY))
                    pressedDirection = DPadDirection.Right;
                else if (leftRect.contains(touchX, touchY))
                    pressedDirection = DPadDirection.Left;
                else if (upRect.contains(touchX, touchY))
                    pressedDirection = DPadDirection.Up;
                else if (downRect.contains(touchX, touchY))
                    pressedDirection = DPadDirection.Down;

                if (pressedDirection != DPadDirection.None)
                    idDPad = event.getPointerId(0);    
            }              

        return true;
    }

Answer 1

Given what you've told me in your comment, you can do something like this:

float touchX, touchY;

public boolean onTouchEvent(MotionEvent event)
{
        if (event.getAction() == MotionEvent.ACTION_DOWN || 
            event.getAction() == MotionEvent.ACTION_MOVE)
        {   
           // store values
           touchX = event.getX();
           touchY = event.getY();
        } else if(event.getAction() == MotionEvent.ACTION_UP) 
        {
           // reset values
           touchX = 0f;
           touchY = 0f;
        }     
        // consume motion event
        return true;
}

In action_down or action_move, you store the event.getX() and event.getY() coordinates in a field outside the onTouchEvent class. Then in your update loop, before you do anything with the pressedDirection, you have your code:

           if (rightRect.contains(touchX, touchY))
             pressedDirection = DPadDirection.Right;
            else if (leftRect.contains(touchX, touchY))
                pressedDirection = DPadDirection.Left;
            else if (upRect.contains(touchX, touchY))
                pressedDirection = DPadDirection.Up;
            else if (downRect.contains(touchX, touchY))
                pressedDirection = DPadDirection.Down;

            if (pressedDirection != DPadDirection.None)
                idDPad = event.getPointerId(0);    

           // do something based on pressedDirection

So in the onTouchEvent you store the values the touch coordinates. In your game loop, you do the checks to see if the coordinates are in the appropriate Rects. Then you run the rest of your game code. You reset the values to zero when the MotionEvent is an ACTION_UP

Answer 2

All the touch points come in a single call. And most of the accessor functions on the MotionEvent class have an overloaded function that takes in pointer index.

So use MotionEvent.getPointerCount() and loop through your mouse pointers.

http://developer.android.com/reference/android/view/MotionEvent.html

Hope this helps.

Answer 3

Remember that many (most?) Android devices don't allow true multitouch; on those phones, once the user is using one finger on your virtual dpad and press elsewhere on the screen at the same time you're going to get random positions sent to your app from the phone and there's nothing you can do about it.