Question

I have a rectangular CGMutablePathRef and I want to subtract a circle which lays exactly on centered on one edge of that rectangle, so the edge does not cross the circle anymore.

There seem to be no functions to intersect or subtract paths from another. How can I do it?

Answer 1

You need to look at the CGContext you are drawing into and use the clipping on the context rather than the path.
Apple’s documentation is here.

If I understand your question, you can draw your rectangle into the context and then “clip out” the circle path. If you are filling the paths, you’ll need to pay attention to the winding rules.

Alternatively, you can make your path with a series of commands such as CGPathAddLineToPoint, CGPathAddArcToPoint, etc and then stoke the path in your context. If you use this approach, you can then apply transforms to the final path for scaling and rotating as needed. Depending on what you are trying to accomplish, this may be the better approach.