Wglswapbuffers takes 4 frames or more to swap

[damian]

I am using WinXP with an NVIDIA card.

I have an app which uses double buffering.

The Monitor refresh rate is 75Hz.

However wglswapbuffers seems to be taking ~47ms (and occasionally a lot longer) to swap. My drawing code is less then 1ms.

I had expected upto a frame to two frames delay, but not a four frame delay.

CPU usage is less then 10%.

Any suggestions as to what may be going wrong?

Thanks Damian

[ZbuffeR]

The GL commands you send are not processed syncronously. The card can render stuff whenever it wants.
To guarantee all GL commands have been actually processed, call glFinish();.

So to benchmark, you should only measure time between glFinish pairs.

EDIT: but of course this comes at the price of loosing some parallelism between GPU and CPU. glFlush(); tells the GPU to process commands but returns immediately.

[damian]

Thanks for the tip.

I found that the problem was with my use of glEnable(GL_TEXTURE_2D) and glDisable(GL_TEXTURE_2D).

It appears that I need to disable the texture as soon as I have finished with it.