четверг, 22 сентября 2011 г.

Non OpenGL ES 2.0 standard compliant iOS

Unfortunately iOS driver is not fully compliant with OpenGL ES 2.0 standard.
During my R&D of best rendering solutions on iOS i found out, that iOS doesn't support texture lookups in vertex shaders! This feature is clearly described in GLSL ES standard. The PowerVR SGX GPUs USSE doesn't care where to do texture lookup - in vertex or in fragment shader. Too bad, that Apple didn't implemented this feature, it gives us additional space to apply our skills. But accidentally i found this article, which describes how to get working texture lookup in vs! Unfortunately it seems to work only on iOS 4.3. I had no luck with couple of iPod 4 with iOS 4.3.1, 4.3.3 and iPad 1\2.
P.S. I'm sure that texture lookup is not the only thing against standard in iOS... 

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