XOR drawing in Cocoa

[Joe Esch" <joe at sketchup.com (Joe Esch)]

I can draw the temporary graphics in OpenGL, but I don't know how to update
them without redrawing the entire scene.  For a large model, this can be
farily slow.

What I am looking for is a way to display some temporary graphics (e.g. a
selection rectangle) over the OpenGL view without having to redraw the
entire OpenGL scene on every mouse move.

I am already using the stencil buffer for computing shadows.

> Quartz does not support XOR drawing.
> For temporary drawing use NSWindow's - cacheImageInRect: and
> - restoreCachedImage
>
> However, I doubt they will work with hardware accelerate OpenGL.  Why not
> just draw your temporary selection lines with OpenGL ?  You could even use
a
> stencil buffer for overlay effects.