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POOpenGL core profile incredible slowdown on OS X
 

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    <p>I added a new GL renderer to my engine, which uses the core profile. While it runs fine on Windows <strike>and/or nvidia cards</strike>, it is like 10 times slower on OS X (3 fps instead of 30). The weird thing is, that my compatibility profile renderer runs fine.</p> <p>I collected some traces with Instruments and the GL profiler:</p> <p><a href="https://www.dropbox.com/sh/311fg9wu0zrarzm/31CGvUcf2q" rel="nofollow">https://www.dropbox.com/sh/311fg9wu0zrarzm/31CGvUcf2q</a></p> <p>It shows that the application spends its time in glDrawRangeElements. I tried the following things:</p> <ul> <li>use glDrawElements instead (no effect)</li> <li>flip culling (no effect on speed)</li> <li>disable some GL_DYNAMIC_DRAW buffers (no effect)</li> <li>bind index buffer after VAO when drawing (no effect)</li> <li>converted indices to 4 byte (no effect)</li> <li>use GL_BGRA textures (no effect)</li> </ul> <p>What I didn't try is to align my vertices to 16 byte boundary <strike>and/or convert indices to 4 byte</strike>, but seriously, if that would be the issue then why the hell does the standard allow it?</p> <p>I'm creating the context like this:</p> <pre><code>NSOpenGLPixelFormatAttribute attributes[] = { NSOpenGLPFAColorSize, 24, NSOpenGLPFAAlphaSize, 8, NSOpenGLPFADepthSize, 24, NSOpenGLPFAStencilSize, 8, NSOpenGLPFADoubleBuffer, NSOpenGLPFAAccelerated, NSOpenGLPFANoRecovery, NSOpenGLPFAOpenGLProfile, NSOpenGLProfileVersion3_2Core, 0 }; NSOpenGLPixelFormat* format = [[NSOpenGLPixelFormat alloc] initWithAttributes:attributes]; NSOpenGLContext* context = [[NSOpenGLContext alloc] initWithFormat:format shareContext:nil]; [self.view setOpenGLContext:context]; [context makeCurrentContext]; </code></pre> <p>Tried on the following specs:</p> <ul> <li>radeon 6630M, OS X 10.7.5</li> <li>radeon 6750M, OS X 10.7.5</li> <li>geforce GT 330M, OS X 10.8.3</li> </ul> <p>Do you have any ideas what I might do wrong? Again, it works fine with the compatibility profile (not using VAOs though).</p> <p><strong>UPDATE</strong>: reported to Apple.</p> <p><strong>UPDATE</strong>: Apple doesn't give a damn to the problem...anyway I created a small test program which is actually good. Now I compared the call stack with Instruments, and found out that when using the engine, <em>glDrawRangeElements</em> does two calls:</p> <ul> <li>gleDrawArraysOrElements_ExecCore</li> <li>gleDrawArraysOrElements_Entries_Body</li> </ul> <p>while in the test program it calls only the second. Now the first call does something like an immediate mode render (gleFlushPrimitivesTCLFunc, gleRunVertexSubmitterImmediate), so obviously casues the slowdown.</p>
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    1. CO"*but seriously, if that would be the issue then why the hell does the standard allow it?*" Because the standard doesn't define *performance*. Only functionality.
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    2. COIt almost sounds like it's falling back to software. You should profile it and see where the slowdown is. Also, can you run it with OpenGL Profiler and turn on all the error breakpoints? It may point out something you're missing (and will tell you if it's falling back to software).
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    3. COI did enable error checking, as well as breaking on sw fallback, but nothing happened. Btw. the log I attached shows that the engine is also checking for GL errors every frame. And as I mentioned the slowdown is clearly in glDrawRangeElements.
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