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/*
SCREENGetFlipInterval.c
AUTHORS:
Allen.Ingling@nyu.edu awi
mario.kleiner.de@gmail.com mk
PLATFORMS: All
HISTORY:
03/10/02 awi Created.
05/09/05 mk Put into use.
DESCRIPTION:
Returns the estimated/measured flip interval for the specified onscreen window surface.
It either returns the value of a previous estimate (e.g., from Screen('OpenWindow',...)) or performs
a measurement run.
*/
#include "Screen.h"
static char useString[] = "[ monitorFlipInterval nrValidSamples stddev ] =Screen('GetFlipInterval', windowPtr [, nrSamples] [, stddev] [, timeout]);";
static char synopsisString[] =
"Returns an estimate of the monitor flip interval for the specified onscreen window.\n"
"\"windowPtr\" is the handle of the onscreen window for which info should be returned.\n"
"\"nrSamples\" If left out, the estimated interval from previous calls to GetFlipInterval "
"or from the initial calibration done during Screen('OpenWindow'...) is reported. "
"If set to a value greater zero, PTB will perform a measurement loop "
"to compute a good estimate. The loop will run until at least nrSamples valid samples have "
"been taken and standard deviation of the measurement is below \"stddev\" seconds. A timeout "
"value \"timeout\" can be set to abort the measurement after timeout seconds if the measurement "
"doesn't converge for some reason. Timeout is 10 seconds and stddev is 50 microseconds by default. "
"PTB automatically takes at least 50 valid samples when opening an onscreen-window, trying to achieve a "
"standard deviation below 100 microseconds, but timing out after a maximum of 15 seconds. "
"If you require very high precision, call this routine with values that suit your demands.\n"
"The returned monitorRefreshInterval is in seconds, but has sub-millisecond accuracy. "
"The real number of valid samples taken and the final standard deviation is returned as well.\n"
"CAUTION: When using frame-sequential stereo (stereomode=1/11 in OpenWindow), "
"the flip interval (as reported here) may be twice as long as the monitor refresh interval. Using "
"Anti-Aliasing with a high multiSample level at a high display resolution may also cause the graphics "
"hardware to switch to a flip-interval twice as long as the monitor refresh interval, because it is "
"not capable of performing all anti-aliasing computations in one single refresh interval.";
static char seeAlsoString[] = "OpenWindow, Flip, NominalFrameRate";
PsychError SCREENGetFlipInterval(void)
{
PsychWindowRecordType *windowRecord;
double ifi_estimate=0;
double maxsecs=10; // Time-out after ten seconds by default.
double stddev=0.00005; // Require a std-deviation less than 50 microseconds by default..
int nrSamples=0;
double ifi_hint;
//all subfunctions should have these two lines.
PsychPushHelp(useString, synopsisString, seeAlsoString);
if (PsychIsGiveHelp()) {PsychGiveHelp(); return(PsychError_none); };
PsychErrorExit(PsychCapNumInputArgs(4)); //The maximum number of inputs
PsychErrorExit(PsychRequireNumInputArgs(1)); //The required number of inputs
PsychErrorExit(PsychCapNumOutputArgs(3)); //The maximum number of outputs
//get the window record from the window record argument and get info from the window record
PsychAllocInWindowRecordArg(kPsychUseDefaultArgPosition, TRUE, &windowRecord);
if (windowRecord->windowType != kPsychDoubleBufferOnscreen) {
PsychErrorExitMsg(PsychError_user, "GetFlipInterval called on window without backbuffers.");
}
// Query number of valid samples to take for calibration. Defaults to zero = Just query, don't measure...
PsychCopyInIntegerArg(2, FALSE, &nrSamples);
if (nrSamples < 0) {
PsychErrorExitMsg(PsychError_user, "nrSamples must be greater or equal to zero.");
}
// Query threshold for stddev... Defaults 50 microseconds jitter.
PsychCopyInDoubleArg(3, FALSE, &stddev);
if (stddev < 0.00002) {
PsychErrorExitMsg(PsychError_user, "stddev must be greater or equal to 0.00002 secs aka 20 microseconds.");
}
// Query timeout... Defaults to 10 seconds.
PsychCopyInDoubleArg(4, FALSE, &maxsecs);
if (maxsecs <= 0) {
PsychErrorExitMsg(PsychError_user, "maxsecs must be greater than zero seconds.");
}
// Query framerate / ifi-estimate from operating system:
ifi_hint = PsychGetNominalFramerate(windowRecord->screenNumber);
if (ifi_hint > 0) {
// Valid nominal framerate reported. Use it as ifi_hint:
ifi_hint = 1.0 / (double) ifi_hint;
}
else {
// Invalid os reporting. Use ifi_beamestimate instead, as measured by
// beamposition query based video refresh measurement during onscreen
// window creation:
ifi_hint = windowRecord->ifi_beamestimate;
}
// Backend override active for external display backend?
if (windowRecord->imagingMode & kPsychNeedFinalizedFBOSinks) {
// Yes: Report "made up" values injected from external backend, instead
// of the ones associated with this windows windowing system screen:
ifi_estimate = windowRecord->VideoRefreshInterval;
nrSamples = 1;
stddev = 0.0;
}
else {
ifi_estimate = PsychGetMonitorRefreshInterval(windowRecord, &nrSamples, &maxsecs, &stddev, ifi_hint, NULL);
if (ifi_estimate == 0)
PsychErrorExitMsg(PsychError_user, "GetFlipInterval failed to compute good estimate of monitor refresh! Somethings screwed up with VBL syncing!");
}
// Return the measured IFI:
PsychCopyOutDoubleArg(1, FALSE, ifi_estimate);
// Return number of valid samples taken:
PsychCopyOutDoubleArg(2, FALSE, nrSamples);
// Return standard deviation of measurement (jitter):
PsychCopyOutDoubleArg(3, FALSE, stddev);
// Done.
return(PsychError_none);
}
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