Horizontal overlay causes the left and right halves of the video frame to be
treated as two separate images which are composited, or blended. The resulting
blended image is then stretched to fill the entire display. As an example, if
the graphics board is generating a 2048x768 image, then the final display would
consist principally of the left 1024x768 image, with some parts overlayed by the
right 1024x768 image. The compositing is done within the rectangle defined by
-“boundsRect” is a 4-element array containing the left/top/right/bottom pixel
coordinates of the compositing rectangle. Within this bounding rectangle, the
two images are blended according to an alpha function which is defined by
calling Datapixx(‘SetVideoHorizontalOverlayAlpha’, alphaTable). Because
SetVideoHorizontalOverlayBounds can be called many times per video frame,
horizontal overlays can be used to generate very low latency gaze-contingent
displays, without having to wait for OpenGL to page flip.
See DatapixxGazeContingentDemo.m for an example.