Android masking with canvas drawing

Question

I'm attempting to create a mask by drawing lines on a canvas. However, when I finish with the image it's just of the original image. If I send the mask bitmap it shows as expected and the original image is correct. How can I get the masking to work between the two bitmaps?

@Override
public void onDraw(Canvas canvas) {
    if (lines == null) {
        return;
    }
    Bitmap mask = null;
    if(performMask) {
        mask = Bitmap.createBitmap((int)getWidth(), (int)getHeight(), Bitmap.Config.RGB_565);
        canvas = new Canvas(mask);
    }

    for (int i = 0; i < lines.size(); i++) {
        ArrayList<Point> line = lines.get(i);
        for (int j = 1; j < line.size(); j++) {
            Point start = line.get(j - 1);
            Point end = line.get(j);
            canvas.drawLine(start.x, start.y, end.x, end.y, drawingPaint);
        }
    }

    if(performMask) {
        performMask = false;

        Bitmap result = Bitmap.createBitmap(original.getWidth(), original.getHeight(), Bitmap.Config.ARGB_8888);
        Canvas tempCanvas = new Canvas(result);
        Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
        paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));
        tempCanvas.drawBitmap(original, 0, 0, null);
        tempCanvas.drawBitmap(mask, 0, 0, paint);
        paint.setXfermode(null);
        if(maskPerformedListener != null) {
            maskPerformedListener.onMaskCompleted(result);
        }
    }
}

Answer 1

I needed to change this line

mask = Bitmap.createBitmap((int)getWidth(), (int)getHeight(), Bitmap.Config.RGB_565);

to

mask = Bitmap.createBitmap((int)getWidth(), (int)getHeight(), Bitmap.Config.RGB_8888);

Turns out you need the alpha layer for this to work.