>Psychtoolbox>PsychGLImageProcessing

rval = kPsychSkipTimestampingForFlipOnce

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 waiting for flip completion (= stimulus onset)
as well as visual stimulus onset timestamping and timing correctness
checks during execution of the next Screen(‘Flip’) operation.