numFrames Number of grating textures to use for the drifting grating…
ifis = Number of monitor refreshes to wait between drawing single
OS X: ___________________________________________________________________
This illustrates an application of Alpha blending by masking the rotating
grating with a gaussian transparency mask.
In each frame, first the grating is drawn. Then a texture acting as a
transparency mask is drawn “over” the grating, masking out selected
parts of the grating.