Drawing on Canvas - PorterDuff.Mode.CLEAR draws black! Why?
PorterDuff.Mode.CLEAR doesn't work with hardware acceleration. Just set
view.setLayerType(View.LAYER_TYPE_SOFTWARE, null); Works perfectly for me.
Use this statement during initialization of the view
setLayerType(LAYER_TYPE_HARDWARE, null);
Everything is ok in your code except one thing: you get black background because your window is opaque. To achieve transparent result you should draw on another bitmap. In your onDraw method please a create new bitmap and do all the staff on it. After that draw this bitmap on your canvas.
For details and sample code please read this my answer: