Perfect timing. This is just as I was working on my own Finder recreation, albeit idealized and a list view. So I'm adding in my offering (linked to by the name), which is some utility functions and categories to bridge IconRefs and UTIs into NSImages. This includes the darkened/selected icon and folder icons.

Elsewhere, for roundrects, I cheated and just used:
[drawnLine setLineJoinStyle:NSRoundLineJoinStyle]; [drawnLine setLineWidth:ourRadius]; [drawnLine appendBezierPathWithRect:ourHilightRect]; [drawnLine fill]; [drawnLine stroke];
Admittedly, this only works for a single-color roundrect.