rval = kPsychNeedTwiceWidthWindow

Return a flag that you can pass to the ‘imagingmode’ parameter of
Screen(‘OpenWindow’) in order to request use of twice-width windows.
These onscreen windows are treated by all drawing functions (and geometry
query functions like Screen(‘Rect’, window); or Screen(‘WindowSize’,
window); as if they have twice the width of the underlying framebuffer in

This is used for special packed-pixel display modes, where the content of
two visual stimulus pixels is packed into one single output framebuffer
pixel for video scanout. E.g., certain special medical displays for use
in Radiology (cfe. “Eizo RadiForce GS-520”) are able to display
calibrated pure luminance images with a luminance precision of 12 bits
per grayscale pixel at 5 Megapixels resolution. These displays are driven
over a single-link DVI-D interface with a special pixel data transmission
format: Two horizontally adjacent 12-bit luminance pixels are encoded
into one 24-bit RGB pseudo-color pixel. This requires a framebuffer
encoding two luminance pixels in a single RGB8 output pixel, ie. the
stimulus image in its “natural” representation is twice as wide as the
underlying scanout framebuffer of the stimulus window. For such use cases
we need the ability to have twice-width windows.

Usually user scripts won’t pass this flag, but only special setup
routines that are part of the Psychtoolbox itself.

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