[visionegg] WARNINGs in the log file

Dear Andrew,

Thank you for the code you sent me last week! I have a question concerning
the use of this code (see below, second code part). When I run the program
with this code and set the duration_per_image at 0.1 sec. I can see that the
duration of display differs per image. Also, several WARNINGs occur in the
VisionEgg log file (see here):

*********************************************
VisionEgg info (2002-11-27 17:00:57): C:\Documents and Settings\j.lacroix\My
Documents\python\stimuli.py
    started.
VisionEgg info (2002-11-27 17:01:03): Requesting window 768 x 576 32 bpp (8
8 8 0 RGBA).
VisionEgg info (2002-11-27 17:01:05): OpenGL 1.3.1, GeForce2 MX/PCI/SSE2,
NVIDIA Corporation
VisionEgg info (2002-11-27 17:01:05): Video system reports 32 bpp (8 8 8 0
RGBA).
VisionEgg WARNING (2002-11-27 17:01:16): Calculated frames per second was
9.440, while the
    VISIONEGG_MONITOR_REFRESH_HZ variable is 100.0.
VisionEgg WARNING (2002-11-27 17:01:16): One or more frames took 582.3 msec,
which is signficantly
    longer than the expected inter frame interval of 10.0 msec for your
frame rate (100.0 Hz).
VisionEgg  info (2002-11-27 17:01:17): During the last "go" loop, 19 frames
were drawn.
Longest frame was 582.25 msec.
histogram:
    10
*
     9
*
     8
*
     7
*
     6
*
     4
*
     3
*
     2                                                                  *
*
     1                                                        *         *
*
     0                                    *         *    *    *         *
*
 Time:    0    2    4    6    8   10   12   14   16   18   20   22   24   26
28   30   32   34   36 +(msec)
Total:      0    0    0    0    0    0    1    0    1    1    2    0    3
0    0    0    0    0    11
***************************************************************************
My videocard is nVidea GeForce MX 100/200 and the refresh rate is set at 100
herz. I work with windows 2000
Could you please explain why I still get these warnings.

Thank you in anticipation!

Kind regards, Joyca Lacroix
j.lacroix@xxxxxxxxxxxxx


----- Original Message -----
From: "Andrew Straw" <andrew.straw@xxxxxxxxxxxxxxx>
To: <visionegg@xxxxxxxxxxxxx>
Sent: Friday, November 22, 2002 2:15 AM
Subject: [visionegg] Re: timing in vision egg


>
> Hi Joyca,
>
> It's within a single "go loop" that the Vision Egg is able to maintain
> timing accuracy, but your code starts a "go loop" each time you want to
> display a new stimulus.  The go loop itself is lasting the duration you
> specify. Because your program doesn't clear the screen after the go
> loop finishes, the last frame drawn is displayed for too long -- the
> duration it takes for the next go loop to start.  In this case, an
> image must be read in from file, so it takes a while.  The simplest
> solution is to pre-load all your images like this:  (This would
> minimize the wait, although it still may not be absolutely temporally
> precise because multiple go loops are still spawned.)
>
> *****************************************************
> preloaded_stimulus_list = []
> for i in range(0, len(photoX)):
>      texture = TextureFromFile(photoX[i])
>      stimulus = TextureStimulus(texture = texture,
>                             size    = texture.orig.size,
>                             shrink_texture_ok=1)
>      preloaded_stimulus_list.append( stimulus )
>
> viewport = Viewport(screen=screen)
> p = Presentation(go_duration=(0.5,'seconds'),viewports=[viewport])
>
> for i in range(0, len(photoX)):
>      viewport.parameters.stimuli = [preloaded_stimulus_list[i]]
>      p.go()
> *****************************************************
>
> The "ultimate" way would be to do everything in a single go loop,
> thereby ensuring timing across all your images.  This requires a
> Controller to select the image used.
>
> *****************************************************
> duration_per_image = 0.5 # seconds
> num_images = len(photoX)
>
> # Create list of stimuli
> preloaded_stimulus_list = [] # empty at first
> for i in range(num_images):
>      # Read the texture file
>      texture = TextureFromFile(photoX[i])
>
>      # Load the texture to OpenGL, prepare for display
>      stimulus = TextureStimulus(texture = texture,
>                          size    = texture.orig.size,
>                          shrink_texture_ok=1)
>
>      # Add to list of stimuli
>      preloaded_stimulus_list.append( stimulus )
>
> def image_selector( t ):
>      i = int(t/duration_per_image)
>      return [ preloaded_stimulus_list[i] ]
>
> viewport = Viewport(screen=screen)
> p = Presentation(go_duration=(duration_per_image *
> num_images,'seconds'),viewports=[viewport])
> p.add_controller(viewport,'stimuli',
> FunctionController(during_go_func=image_selector) )
> p.go()
> *****************************************************
>
> Hopefully this helps.
>
> Cheers!
> Andrew
>
> On Thursday, November 21, 2002, at 09:08  PM, Joyca Lacroix wrote:
>
> > L.S.
> >
> > Currently I'm working on a psychological experiment in which I present
> > (timed) images of faces (tif format). I'm trying to present the images
> > in a sequence, every image for 1 second. Because I have only just
> > begun using vision egg I took one of the demo's in the VisionEgg
> > folder as a strating point (texture.py).
> > I notice that when I present the pictures, the timing becomes less and
> > less precise (after a few images the presentation takes up to 2 sec.
> > and this delay becomes larger and larger)
> > here is part of my code:
> > ************************************************
> > for i in range(0, len(photoX)):
> >     texture = TextureFromFile(photoX[i])
> >     stimulus = TextureStimulus(texture = texture,
> >                            size    = texture.orig.size,
> >                            shrink_texture_ok=1)
> >     viewport = Viewport(screen=screen,
> >                     stimuli=[stimulus])
> >     p = Presentation(go_duration=(0.5,'seconds'),viewports=[viewport])
> >
> >     p.go()
> > *****************************************************
> >
> > Can you help me get the timing more precise? (the problem is not my
> > videocard)
> >
> > Thank you in anticipation
> > Greetings, J.L.
> >
> > j.lacroix@xxxxxxxxxxxxx
> > ======================================
> > The Vision Egg mailing list
> > Archives: http://www.freelists.org/archives/visionegg
> > Website: http://www.visionegg.org/mailinglist.html
>
> ======================================
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