Android canvas: draw transparent circle on image

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So finally I managed to do this.

Firstly I draw a semitransparent black rectangle on whole view.
After that using PorterDuff.Mode.CLEAR I cut a transparent circle to show cat’s position.

I had problem with PorterDuff.Mode.CLEAR: firstly I was getting a black circle instead of a transparent one.

Thanks to Romain Guy’s comments here: comment here I understood that my window is opaque and I should draw on another bitmap. And only after draw on View‘s canvas.

Here is my onDraw method:

private Canvas temp;
private Paint paint;
private Paint p = new Paint();
private Paint transparentPaint;

private void init(){
    Bitmap bitmap = Bitmap.createBitmap(canvas.getWidth(), canvas.getHeight(), Bitmap.Config.ARGB_8888);
    temp = new Canvas(bitmap);
    paint = new Paint();
    paint.setColor(0xcc000000);
    transparentPaint = new Paint();
    transparentPaint.setColor(getResources().getColor(android.R.color.transparent));
    transparentPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
}

protected void onDraw(Canvas canvas) {
    temp.drawRect(0, 0, temp.getWidth(), temp.getHeight(), paint);
    temp.drawCircle(catPosition.x + radius / 2, catPosition.y + radius / 2, radius, transparentPaint);
    canvas.drawBitmap(bitmap, 0, 0, p);
}

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