CGContext: how do I erase pixels (e.g. kCGBlendModeClear) outside of a bitmap context?

Question

I\'m trying to build an eraser tool using Core Graphics, and I\'m finding it incredibly difficult to make a performant eraser - it all comes down to:

CGContextSetB

Answer 1

key is CGContextBeginTransparencyLayer and use clearColor and set CGContextSetBlendMode(context, kCGBlendModeClear);