function DriftDemo3([cyclespersecond=1][, p=32])
Display an animated grating using the new Screen(‘DrawTexture’) command.
In the OpenGL-Psychtoolbox Screen(‘DrawTexture’) replaces
Screen(‘CopyWindow’). The demo will stop after 60 seconds have
passed or after the user hits a key.
This demo illustrates how to draw an animated grating online by use of
only one grating texture with the minimal amount of code and complexity.
It is restricted in that the spatial period of the grating in pixels
must divide the total size of the pattern without remainder and that the
size of the grating in pixels must be a power of two, e.g., 256 or 512 or
- For a more complex but more general solution which allows for
arbitrary grating sizes and also masked gratings, see DriftDemo2. For a
very fast and efficient method, which only works on recent graphics
hardware, see DriftDemo4.
We create one single texture with a static sine grating. The texture
is a power-of-two texture, one whose width and height are powers of two.
Such textures can be drawn in a special scrolling mode, as if they
would extend in each direction to infinity, periodically repeating
the pattern of the texture image in each direction.
In each successive frame we draw a rectangular region of the sine
texture onto the screen that is the size of the texture. This region,
the ‘srcRect’ in the Screen(‘DrawTexture’) command, is shifted each
frame. As the graphics hardware makes our special texture to appear as if
it is repeating infinitely into each direction, we create the impression of
a moving grating.
cyclespersecond = Speed of grating in cycles per second.
p = Spatial period of grating in pixels.
CopyWindow vs. DrawTexture:
In the OS 9 Psychtoolbox, Screen (‘CopyWindow”) was used for all
time-critical display of images, in particular for display of the movie
frames in animated stimuli. In contrast, Screen(‘DrawTexture’) should not
be used for display of all graphic elements, but only for display of
MATLAB matrices. For all other graphical elements, such as lines, rectangles,
and ovals we recommend that these be drawn directly to the display
window during the animation rather than rendered to offscreen windows
prior to the animation.