Is its possible to enable GPU in after effects cs6 on mac mountain lion with Intel HD 4000?
No, OpenGL Swap Buffer support (Level 1) support for the HP4000 is for Windows only. Level 2 and 3 support is not available either. You'd need a more powerful NVIDIA card for Level 1, 2, and 3 feature support.
More info here: http://helpx.adobe.com/after-effects/using/rendering-opengl.html#main-pars_header_3
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