help -- timing problem

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From: Fangtu Qiu (qiu++at++jhu.edu)
Date: 01/11/2000 13:25:53

Hi,

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?

Thanks.

Fangtu

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