Canvas.Copy is taking too long to complete

Thu Apr 25 05:19:52 UTC 2013

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 
> Twitter:  @EPrimeMaster (twitter.com/EPrimeMaster) 
>
> /----------- 
> Stock reminder:  1) I do not work for PST.  2) PST's trained staff take 
> any and all questions at 
> http://support.pstnet.com/e%2Dprime/support/login.asp , and they strive 
> to respond to all requests in 24-48 hours, so make full use of it.  3) 
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> ), and offers several instructional videos there and on their YouTube 
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> though).  4) If you do get an answer from PST staff, please extend the 
> courtesy of posting their reply back here for the sake of others. 
> \----------- 
>
>
> 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 <javascript:> [mailto:
> e-p... at googlegroups.com <javascript:>] *On 
> > Behalf Of *Tamar 
> > *Sent:* 24. April 2013 08:33 
> > *To:* e-p... at googlegroups.com <javascript:> 
> > *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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