Question

How do I draw a Rect that basically creates a hole in the canvas? For example, say I have an image editing application that’s made for Pixel art. The user touches an area of the screen, and draws a purple rectangle. Oops, he put the rectangle in the wrong spot. The user needs to make this purple square turn transparent again so that he can re-draw it in the right position.

How do I do this? I’ve used PorterDuff.Mode.Clear, myPaintColor.setColor(Color.TRANSPARENT) etc. but all give the same result. An ugly black square where it should be transparent. My canvas starts out as transparent, and can be saved via getDrawingCache to a transparent .PNG, so I know the canvas starts off as transparent. But how do I help my user who drew the purple square to make his canvas transparent again? Thanks. I’ve been trying to figure this out all day, reading all the documentation on this, but I can’t figure it out.

Here’s what I have:

            Rect square = new Rect();
            Paint drawColor = new Paint();
            //drawColor.setColor(UserColor.get(i));
            drawColor.setXfermode(new PorterDuffXfermode(Mode.CLEAR));
            square.set(CanvasFractionWidth * UserX.get(i), CanvasFractionHeight * UserY.get(i), (CanvasFractionWidth * UserX.get(i)) + (CanvasFractionWidth), (CanvasFractionHeight * UserY.get(i)) + CanvasFractionHeight);
            canvas.drawRect(square, drawColor);

Answer 1

In RoboDemo, I use this :

        Paint p = new Paint();
        p.setXfermode( new PorterDuffXfermode( Mode.CLEAR ) );