Is it possible to render core graphics / cocoa drawing functions
(such as bezier paths, shadows, image clipping) to an openGL context?
Not directly.
Or can one only use openGL drawing functions to draw to an openGL
context?
I can think of a few options. If you have some Quartz or Cocoa stuff
to draw over the top, you can create a transparent window, making it
a child of the window with the OpenGL view in it (see -
addChildWindow:ordered:), and draw your Quartz content into that.
This is quite easy and should be pretty fast.
Alternatively, if you want to draw things you've rendered with Quartz
into an OpenGL context, you can always use a bitmap graphics context
(or lock focus on an NSBitmapImageRep), then draw the resulting
bitmap to your OpenGL context somehow (e.g. by creating a texture and
drawing a quad, or by calling glDrawPixels()). If the Quartz/Cocoa
drawing isn't changing very much over time, it's probably best to
make a texture (since glDrawPixels() will send the image data to the
graphics card every time, instead of caching it there).
Sometimes you might also be able to get Quartz Composer to draw what
you need, in which case you can just use that instead via a QCView.
I don't know if there are any other ways, but the two above should
suffice for most purposes I think.
