Here is a solution which helped me to implement masking:
public void draw(Canvas canvas) {
Bitmap original = BitmapFactory.decodeResource(getContext().getResources(),R.drawable.original_image);
Bitmap mask = BitmapFactory.decodeResource(getContext().getResources(),R.drawable.mask_image);
//You can change original image here and draw anything you want to be masked on it.
Bitmap result = Bitmap.createBitmap(mask.getWidth(), mask.getHeight(), Config.ARGB_8888);
Canvas tempCanvas = new Canvas(result);
Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
paint.setXfermode(new PorterDuffXfermode(Mode.DST_IN));
tempCanvas.drawBitmap(original, 0, 0, null);
tempCanvas.drawBitmap(mask, 0, 0, paint);
paint.setXfermode(null);
//Draw result after performing masking
canvas.drawBitmap(result, 0, 0, new Paint());
}
The mask should be a white image with transparency.
It will work like this:
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