Android canvas - Draw a hole

问题:

Is it possible to realize the following picture in Android with canvas?

I want to have a hole and not only a Circle over the red layer which is yellow colored. I tried this (and failed) with the following Code in my onDraw()-Method:

canvas.drawBitmap(yellow, 0, 0, paint);
canvas.drawBitmap(red, 0, 200, paint);
Paint p = new Paint();
p.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
canvas.drawCircle(300, 300, radius, p);

But when I use this code, it makes a hole through both bitmap's. At the end, this App should be a Maze with a ball, holes and other stuff. When the ball would fall into a hole it should appear under the red-Bitmap. Is it possible to realize this?

Answer:

If someone should have the same problem: use View and not SurfaceView. That was my fault, because the bg of a SurfaceView could not be set transparent.

回答1:

I think you're misunderstanding how the canvas/bitmaps work. There aren't layers or objects stored (unless you store them). It's just a pixel by pixel representation of the image displayed. A yellow circle over a red square is what you have shown in the above picture.

If you truly want a red layer, you have to composite two bitmaps. Draw the hole over the red square in one bitmap, draw the yellow layer in one bitmap. On the canvas, draw the yellow bitmap, then the "red square with a hole" bitmap on top.