Drawing on Canvas - PorterDuff.Mode.CLEAR draws black! Why?

Question

I'm trying to create a custom View which works simple: there is a Bitmap which is revealed by arc path - from 0deg to 360deg. Degrees are changing with some FPS.

So I made a custom View with overridden onDraw() method:

@Override protected void onDraw(Canvas canvas) {      canvas.drawColor(Color.TRANSPARENT, PorterDuff.Mode.CLEAR);     arcPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC));     canvas.drawArc(arcRectF, -90, currentAngleSweep, true, arcPaint);     arcPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));     canvas.drawBitmap(bitmap, circleSourceRect, circleDestRect, arcPaint); } 

arcPaint is initialized as follows:

arcPaint = new Paint(); arcPaint.setAntiAlias(true); arcPaint.setColor(Color.RED); // Color doesn't matter 

Now, everything draws great, but... the background is BLACK in whole View.

If I set canvas.drawColor(..., PorterDuff.Mode.DST) and omit canvas.drawBitmap() - the arc is drawn properly on transparent background.

My question is - how to set PorterDuff modes to make it work with transparency?

Of course bitmap is 32-bit PNG with alpha channel.

Answer 1

PorterDuff.Mode.CLEAR doesn't work with hardware acceleration. Just set

view.setLayerType(View.LAYER_TYPE_SOFTWARE, null);  

Works perfectly for me.