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Monitoring GPU Use

Applications that can’t use the GPU for some reason (such as the graphics card does not support some of the OpenGL extensions that your code uses) use the software renderer as a fallback. If you notice a drop in the performance of your application, you may want to check whether the application is using the GPU as you expect.

Starting in Mac OS X v10.5, you can set your application to break whenever it uses the software renderer as a fallback. (See “Checking for Application Errors, Thread Conflicts, and Software Fallbacks.”) Prior to Mac OS X v10.5, you can monitor the GPU use of your application whenever your application pauses at a breakpoint. The best breakpoints to check are:

• CGLFlushDrawable

• After glUseProgramObjectARB

• After glBindProgramARB

• Any glDraw or related command, including the following:

  • glAccum

  • glBegin

  • glBlitFramebufferEXT

  • glBitmap

  • glClear

  • glCopyPixels

  • glDrawPixels

  • glReadPixels

  • glCopyTexSubImage*D

  • glCopyTexImage*D

  • glDrawArrays

  • glDrawElements

  • glDrawRangeElements

When your application pauses at these breakpoints, check the values of kCGLCPGPUFragmentProcessing and kCGLCPGPUVertexProcessing shown in the Call Stack pane of the Breakpoints window. A value of GL_TRUE indicates that your application is using the GPU for the process associated with the constant.

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