Great question and of course equally great answer. Thank you for posting these. The bitmap CGContext is a tricky animal. I was trying to clip an image to a circle and whatever stands outside the arc got filled with black. Tried different approaches till I got it working the way you did. Was going to publish the solution when I found your Q/A. If you think the solution is only logical. But the lack of detailed docs and some high expectations can make one struggle. Again, thank you for sharing.