Erase bitmap parts using PorterDuff mode

Here is working code… may help somebody

public class ImageDemo extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(new Panel(this));   
    }

    class Panel extends View {

        private Bitmap  mBitmap;
        private Canvas  mCanvas;
        private Path    mPath;
        private Paint   mPaint;

        Bitmap bitmap;
        Canvas pcanvas;

        int x = 0;
        int y =0;
        int r =0;

        public Panel(Context context) {
            super(context);

            Log.v("Panel", ">>>>>>");

            setFocusable(true);
            setBackgroundColor(Color.GREEN);

            // setting paint 
            mPaint = new Paint();
            mPaint.setAlpha(0);
            mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));
            mPaint.setAntiAlias(true);

            // getting image from resources
            Resources r = this.getContext().getResources();

            Bitmap bm = BitmapFactory.decodeResource(getResources(),  R.drawable.mickey);

            // converting image bitmap into mutable bitmap  
            bitmap =  bm.createBitmap(295, 260, Config.ARGB_8888);
            pcanvas = new Canvas();
            pcanvas.setBitmap(bitmap);    // drawXY will result on that Bitmap
            pcanvas.drawBitmap(bm, 0, 0, null);           
        }

        @Override
        protected void onDraw(Canvas canvas) {  
            // draw a circle that is  erasing bitmap            
            pcanvas.drawCircle(x, y, r, mPaint);

            canvas.drawBitmap(bitmap, 0, 0,null);

            super.onDraw(canvas);
        }       

        @Override
        public boolean onTouchEvent(MotionEvent event) {        
             // set parameter to draw circle on touch event
             x = (int) event.getX();
             y = (int) event.getY();

             r =20;
             // At last invalidate canvas
             invalidate();
             return true;
        }
    }
}