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c++timing

glXSwapBuffers glitchy timing

I have been getting very glitchy timings in my render loop causing rendering to stutter. I have set up timing around my glXSwapBuffers call like so:

Timer timer;
glXSwapBuffers(display, window);
timer();
if (timer.elapsed_seconds > 0.1)
 printf("stutter(%f)\n\r", timer.elapsed_seconds);

And am getting results like:

stutter(0.109081)
stutter(0.108956)
stutter(0.662115)
stutter(0.759556)
stutter(0.657789)
stutter(0.283185)
stutter(0.105581)
stutter(0.106285)
stutter(0.572289)
stutter(0.199908)
stutter(0.218540)
stutter(0.752033)
stutter(0.148225)

What could be causing glXSwapBuffers to take so long to call? How can I fix the stuttering?

Solution

  • After much testing and debugging I found that my Timer class was computing the difference between two timestamps wrong. The tv_nsec component was being incorrectly divided causing elapsedSeconds to return varying results.

    After correcting this the stuttering went away immediately.