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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."
"\"windowPtr\" is the handle of the onscreen window for which info should be returned. "
"\"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. "
"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. "
"CAUTION: When using OpenGL flip-frame stereo (stereomode=1 in OpenWindow) on ATI graphics hardware, "
"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 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;
}
ifi_estimate = PsychGetMonitorRefreshInterval(windowRecord, &nrSamples, &maxsecs, &stddev, ifi_hint, NULL);
// Child protection:
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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