I’d guess doing the C APIs for CoreGraphics and using those under AppKit would be a way.

CoreFoundation already (partly) exists for FoundationKit support though I’d probably grab the GNUStep code for that.

Any old Carbon APIs might be a hassle.

Compositing is where it’d get tricky even with Ghostscript. It’d be slow without hardware support.

Impressed they can load dyld though. That’s a tricky thing to do.