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Re: Mouse Pointer in OS X. Methodology behind it's "graphics layer". Micah Dowty Wed Feb 25 17:00:35 2009

Is there a requirement that both the bottom (slow) and top
(low-latency) layers are rendered in OpenGL? You might try rendering
the bottom layer with OpenGL, and the top layer in Quartz. AFAIK that
will end up letting the Mac OS window server do the compositing, and
it's used to doing such things relatively quickly and at every
vertical refresh if necessary.

I haven't tried this myself, but check out NSOpenGLCPSurfaceOrder. You
can select whether the OpenGL surface or the normal Quartz window
surface is on top. Either surface can have transparent 'holes' that
let you see the surface below.

Alternatively, you can get nearly the same effect using a movable
child window. That window would float above your OpenGL scene, and it
could move around even when your GL rendrer is busy.

Unfortunately, none of these situations will help you if your OpenGL
renderer is loading down the GPU really heavily. It's not that hard to
overload the GPU to the point where even the window server (And other
applications!) bog down, since there are systemwide locks involved and
the window server itself needs OpenGL too.

Good luck!

--Micah
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