From: Phil Keslin (philk++at++cthulhu.engr.sgi.com)
Date: 01/11/2000 13:30:04
Yair Kurzion wrote:
>
> > 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.
>
This behaviour is implementation specific. On SGI systems, the application will
wait until the swap is completed before proceeding.
- Phil
-- Phil Keslin <philk++at++engr.sgi.com>
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