[VBLTimestamp StimulusOnsetTime swapCertainTime] = Screen(‘WaitUntilAsyncFlipCertain’, windowPtr);
Wait until it is certain that a previously initiated
Screen(‘AsyncFlipBegin’,…); operation for onscreen window ‘windowPtr’ will
happen at next vertical retrace or has happened already, then return timestamps
of when flip operation has happened or when the flip operation will happen.
This function only works on Linux and MacOS/X and only with recent AMD/ATI
hardware of the Radeon X1000/HD2000/… series or later (or the equivalent
FireGL cards). On MacOS/X, the PsychtoolboxKernelDriver needs to be loaded for
this to work (see help PsychtoolboxKernelDriver)).
The method tries to “read the mind” of your graphics card to find out if the
card will swap the display buffers at the next vertical retrace to interrogate
if the swap is certain, ie., not possibly delayed by graphics card overload,
other overload conditions or system timing jitter/delays.
Ideally it will allow your script to know when stimulus onset will happen a few
milliseconds before stimulus onset. This allows, e.g., to initiate some other
operations that need to be tightly and reliably synchronized to stimulus onset
and that have some small startup latency, so they need some headstart. Examples
would be sound output or output of some slow trigger signal which takes multiple
milliseconds to take action.
This feature only works in fullscreen mode and is considered experimental - It
may or may not work reliably on your setup. Good luck!
Returns a high-precision estimate of the system time (in seconds) when the
actual flip will- or has happened in the return argument ‘VBLTimestamp’. An
estimate of Stimulus-onset time is returned in ‘StimulusOnsetTime’.
‘swapCertainTime’ is the system time when certainty of bufferswap was detected.
###See also: ‘AsyncFlipBegin’ ‘AsyncFlipCheckEnd’ ‘AsyncFlipEnd’