>Psychtoolbox>PsychGLImageProcessing

rval = kPsychSkipVsyncForFlipOnce

Return a flag that you can pass as part of the flipFlags for a call to
Screen(‘Hookfunction’, windowPtr, ‘SetOneshotFlipFlags’, flipFlags);

This flag will disable synchronization of OpenGL bufferswaps to
vertical blank (“VBLANK” / “VSYNC”) for the next Screen(‘Flip’) operation.