glmSwapBuffers Swap front and back buffers
usage: [ t, w ] = glmSwapBuffers( pauseflag )
Return argument 't' is the absolute time at which the call to
aglSwapBuffers() returned, and 'w' is the time that aglSwapBuffers()
took to return, i.e., the time spent waiting for a vertical retrace.
These values are useful for checking video timing.
Psychtoolbox/PsychOpenGL/MOGL/wrap/glmSwapBuffers.m