Canvas.Copy is taking too long to complete

Thu Apr 25 05:29:06 UTC 2013

I haven't tested any code examples, but have a 
lot of data showing canvas.copy in v.1.?.? takes 
under a ms, supporting David's observations. 
Perhaps something here is less instant in v2.?, and a bug has been identified?

At 03:19 PM 25/04/2013, you wrote:
>Thank you both your replies!
>
>I am using E-prime 2.0.10, and a CRT iiyama 
>Vision Master screen, with display resolution
>of 1024 x 768 and a refresh rate of 100 Hz. My operating system is windows XP.
>
>I'm troubled with this timing issue because my 
>experiment includes EEG recording, thus the
>synchronization is terribly important. I need to 
>send triggers via the parallel port exactly at the
>onset of each stimulus, or else my EEG signal 
>might be smeared. Considering that the canvas.copy
>takes a refresh cycle to complete - I'm not sure 
>what time ought to be considered the stimulus onset...
>
>Anyhow, David, I've tried running your code - 
>and I get dt's of 13-14ms. Do you think that all the difference
>between your 0.22ms to my 13-14ms is due to 
>E-prime1 vs. E-prime2 differences? That's shocking...
>I get the same results as Michiel for the loop 
>codes, as puzzling as they are...
>
>Thanks again for your help,
>Tamar
>
>
>
>
>On Wednesday, April 24, 2013 4:44:46 PM UTC+3, McFarlane, David wrote:
>Hmm.  I explored this issue myself three years ago, using EP1 (still my
>favorite version for this type of exploration).  I just dug up my test
>program and ran it again on my trusty old XP laptop at home after
>breakfast, and got times of 0.22 ms even for full screen copies, much as
>I remember from before (where full screen means 1024 x 768; and yes,
>that is less than a millisecond).  To be sure, here is the core of my
>test code:
>
>      t0 = clock.readmicrosec
>      dcnvs.copy cnvs
>      dt = clock.readmicrosec - t0
>      msgbox format$( dt/1000, "Standard" ) & " ms"
>
>where all variables are defined and initialized earlier as expected
>(dcnvs is set to Display.Canvas just for notational convenience).
>
>Also, I looked at the Canvas.Copy topic in the E-Basic Help -- no
>evidence that .Copy includes an implicit Display.WaitForVerticalBlank,
>to the contrary, the code example there includes an explicit
>Display.WaitForVerticalBlank just before the cnvs.Copy.  I would be
>*extremely* surprised if Canvas.Copy included a
>Display.WaitForVerticalBlank, as that would greatly compromise its
>utility (e.g., when wanting to Copy several segments to an offscreen
>Canvas before copying the complete result to Display.Canvas).
>
>So I do not know how to account for your results.  Mind you, I did all
>my tests using good-old EP1 with 1024x768 display resolution.  For all I
>know things changed with the latest EP version, or things get slower
>with larger display resolutions.  What EP version do you use?  What
>display resolution?
>
>Michiel, I am especially puzzled by your results.  Both of your tests
>measure the total time to perform a Canvas.Copy and
>Display.WaitForVerticalBlank, only in different orders.  So you should
>get the same time for both tests, regardless of whether Canvas.Copy
>includes its own Display.WaitForVerticalBlank.  What am I missing?
>
>Nevertheless, Michiel's advice still stands  -- as long as your program
>does everything it needs to do within one screen refresh (and assuming
>that you *do* synchronize visual displays to the screen refresh, as you
>should), then that is good enough.
>
>-----
>David McFarlane
>E-Prime training online:
><http://psychology.msu.edu/Workshops_Courses/eprime.aspx>http://psychology.msu.edu/Workshops_Courses/eprime.aspx 
>
>Twitter:  @EPrimeMaster 
>(<http://twitter.com/EPrimeMaster>twitter.com/EPrimeMaster)
>
>/-----------
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>
>
>Cognitology wrote:
> > Hi,
> >
> > A quick look, but I think that you pretty much nailed it: it can take
> > quite long to do any canvas operation. Given that your screen refresh
> > rate presumably isnï¿½t more than 100 Hz (and in any ways, your foveal
> > vision isnï¿½t), I donï¿½t see the problem? 
> Indeed, if you were to draw many
> > things to the main canvas, one after the other, then indeed, it gets to
> > be a problem, but as long as the only 
> operation is copying a ï¿½preloadedï¿½
> > canvas to the shown one, it doesnï¿½t matter all that much. Notice, given
> > that youï¿½re not using E-Primeï¿½s stimdisplays, itï¿½s not clear at what
> > time the stimulus is actually displayed ï¿½ only when itï¿½s done sending
> > the command. I think itï¿½s generally better for critical timing aspects
> > of your experiment to avoid canvas as much as possible. Personally, I
> > think ï¿½critical timingï¿½ is when it concerns a subliminal vs barely
> > supraliminal prime or some such, for other types of stimuli the 10 ms of
> > (constant, therefore presumably stimulus independent) delay is of
> > trivial concern.
> >
> >
> >
> > Just testing some of it myself, and I get values ranging between 15 and
> > 17 ï¿½ which is funny, given that my refresh rate is indeed 60, so it
> > seems a bit like thereï¿½s some sort of display.waitforverticalblank built
> > into canvas.copy. Curiously, this:
> >
> > For j = 1 To 100
> >
> >       DrawFixation ï¿½this is just a custom function drawing a line to
> > cnvsnext
> >
> >       cnvs.copy cnvsnext
> >
> >       display.waitforverticalblank
> >
> >       debug.print clock.read - clocktime
> >
> >       clocktime = clock.read
> >
> > Next j
> >
> >
> >
> > Gives me latencies equal to refresh rates (+- 1 ms).
> >
> > Whereas:
> >
> >
> >
> > For j = 1 To 100
> >
> >       DrawFixation ï¿½this is just a custom function drawing a line to
> > cnvsnext
> >
> >       display.waitforverticalblank
> >
> > cnvs.copy cnvsnext
> >
> >       debug.print clock.read - clocktime
> >
> >       clocktime = clock.read
> >
> > Next j
> >
> >
> >
> > Gives me latencies equal to 2xrefresh rates. Somebody with young eyes
> > should tell us if the first one doesnï¿½t have cutting-off errors,
> > otherwise Iï¿½d suggest there might be some sort of waitforverticalblank
> > built into canvas.copy.
> >
> > Best,
> >
> >
> >
> > Michiel Sovijï¿½rvi-Spapï¿½
> >
> >
> >
> > Helsinki Institute for Information Technology
> >
> > Aalto & University of Helsinki
> >
> > Finland
> >
> >
> >
> >
> >
> >
> >
> > BTW: notice that using debug.print also incurs a delay (last measured at
> > 0.7 ms).
> >
> >
> >
> >
> >
> > *From:* e-p... at googlegroups.com [mailto:e-p... at googlegroups.com] *On
> > Behalf Of *Tamar
> > *Sent:* 24. April 2013 08:33
> > *To:* e-p... at googlegroups.com
> > *Subject:* Canvas.Copy is taking too long to complete
> >
> >
> >
> > I'm programming a visual experiment, and suffering from some timing
> > issues. It seems that the line presenting the stimuli (canvas.copy) is
> > considerably time consuming: 10-12 ms. I can't figure out the cause for
> > this delay, and I would appreciate any help...
> >
> > Here is the relevant piece of code:
> >
> > ====== in an initializing inline script, at the begining of SessionProc:
> > ======
> > Set MainCanvas = Display.Canvas
> > MainCanvas.fillColor = CColor(background_color)
> > MainCanvas.clear
> >
> > For i = 1 To NumStim
> >    Set StimCanvases(i) = Display.CreateCanvas
> >
> >    'define destination rect as center of screen
> >    destRects(i).Left = Display.XRes/2-stim_w/2
> >    destRects(i).Top = Display.YRes/2-stim_h/2
> >    destRects(i).Right = Display.XRes/2+stim_w/2
> >    destRects(i).Bottom = Display.YRes/2+stim_h/2
> >
> >    'define source rect as upper left corner
> >    srcRects(i).Left = 0
> >    srcRects(i).Top = 0
> >    srcRects(i).Right = stim_w
> >    srcRects(i).Bottom = stim_h
> >
> >    'Load the image file
> >    StimCanvases(i).LoadImage "Stimuli/" & FileNames(i) & ".bmp"
> >
> > Next i
> >
> > ====== in the inline of TrialProc: =======
> > Debug.Print "1:" & clock.read
> > StartTrialTime = clock.read
> > n = c.GetAttrib("CanvasNum")
> > c.SetAttrib "TrialStart", StartTrialTime
> > display.WaitForVerticalBlank
> > Debug.Print "4:" & clock.read
> > StartStimTime = clock.read
> > c.SetAttrib "StimStart", StartStimTime
> > Debug.Print "5:" & clock.read
> > mainCanvas.copy StimCanvases(n),srcRects(n),destRects(n)
> > Debug.Print "6:" & clock.read
> >
> >
> > I've tried a few things:
> > - to create variables taking the values of
> > StimCanvases(n),srcRects(n),destRects(n) in the beginning of the trial,
> > so the mainCanvas.copy line would not need to approach the arrays.
> > - to present other simple canvases instead of my real stimuli (just a
> > fixation, for example. or an empty canvas)
> > - to draw something on the mainCanvas rather than copy a new canvas to
> > it (e.g. mainCanvas.Circle).
> >
> > All of these takes 10-12 ms! (as calculated by subtracting time5 from
> > time6). The only way I managed to get rid of the delay was to erase the
> > entire row...
> >
> > Am I missing something here?...
> >
> > Thanks,
> > Tamar
>
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