Re: help -- timing problem

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From: Yair Kurzion (yair++at++polygon.engr.sgi.com)
Date: 01/11/2000 13:25:47

> I need to know the exact time when the graphics card swaps the buffers by
> following method:
>
> glXSwapBuffers
> glXWaitVideoSyncSGI
>
> The glXSwapBuffers only issues the command to swap the buffers and returns
> immediately before the buffers are actually swapped. The command will be
> completed during the next vertical retrace. So, after glXSwapBuffers
> returns, the program calls glXWaitVideoSyncSGI to determine the vertical
> retrace.
>
> Now the problem is that when the glXSwapBuffers returns, sometimes the
> vertical retrace occurs, the graphics card swaps the buffers before the
> program calls glXWaitVideoSyncSGI. Therefore the returning time of
> glXWaitVideoSyncSGI will be one frame later then the actual swapping time
> of the buffers.
>
> Any good method to resolve the problem? Is there any method to access the
> codes that determine the actual swapping of the buffers?

Instead of glXWaitVideoSyncSGI, call

    glNormal3f(0.0f, 1.0f, 0.0f);

(Or any other OpenGL call). This will block until swapbuffers, and will not
wait an extra frame as in your case.

-yair 

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