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stephanh

OpenGL Interleave vertex data or not

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Hi, i always used interleaved vertex buffers, since an old nvidia whitepaper on VBOs suggests to interleave data for optimal performance. Makes sense if one thinks about T&L cache and locality of per-vertex data in case theres a "single" cache. But several posts on the opengl.org forums state that things might be different these days. Does anybody have any information what data layouts recent hardware prefers? Thanks alot. regards, stephan

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I recently wrote some OpenGL benchmarks of my own to answer this exact question, and I found that on my old ATI card, the interleaving had no significant effect on frame rate. On my newer NVidia card the interleaving made an improvement of 10-15% in frame rate, but only when the interleaved array was in a vertex buffer object. When the vertex array was in main memory, the interleaving didn't add much. YMMV.

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I did implement interleaved VBOs in a terrain rendering project recently and it resulted in only 2-3 fps speed up

you gain a lot more speed if you zsort your chunks front to back thus you do a early z fail without an additional rendering pass

thats especially important if you do complex operations in the fragment shader, such as per pixel lighting as we do for the terrain

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I believe interleaving is a few percentage faster on older NVidia hardware. Bavoil has lots of statistics in his MS thesis: http://www.sci.utah.edu/~bavoil/opengl/

Patrick

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