rval = kPsychNeedRetinaResolution

Return a flag that you can pass to the ‘imagingmode’ parameter of
Screen(‘OpenWindow’) in order to allow driving a HiDPI display, aka
Retina-Display at its full native resolution.

Without this flag, Screen() will automatically enable its builtin
panelfitter if it detects the onscreen window being displayed on a Retina
style display, ie., with a scaled HiDPI display mode. The panelfitter
will expose only a smaller, lower resolution framebuffer to the user and
upscale user drawn stimuli to full panel resolution at Screen(‘Flip’).
This is the same behaviour as what OSX normally exposes on a Retina
panel, because it doesn’t cause headaches with various coordinate
transforms, e.g., mouse or touch input coordinates to display coordinates
and vice versa and it puts less load on the GPU, therefore performance
impact is minimized. The downside of this default behaviour is that one
can’t take full advantage of the displays high resolution, apart from

By default Screen() will use the low-level compatibility mode via panel
fitting. If usercode explicitely requests use of the panelfitter via
PsychImaging() tasks, then those requests override Screen’s default

If usercode doesn’t want panelfitting or low-res modes, but the full
native Retina resolution, it can pass this flag to express its wish.
Normally the flag is passed by PsychImaging as part of a more convenient
setup procedure.

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