Re: RFC: invert effect for XRender resp. independent of the compositor

> This is *theoretically* possible for xrender compositing just as for
> OpenGL w/o shaders (ie. not correctly preserving alpha) through
> PictOpDifference, BUT i've tried and it only works on the nvidia blob
> (intel just ignores the call) and is DOOOOOOOG SLOOOOOOW ;-)
>
> For the entire screen it can however be done through
> XF86VidModeSetGammaRamp w/o any overhead.
>
> This approach however actually doesn't require a compositor at all.
>
> Since we're about to conditionally link xvidmode in 4.9 anyway, this is
> somehow about accessibility and there's talk to change the effect config
> UI, i wonder whether we should offer this as shortcut from the core (if
> xvidmode is present) and invert the screen regardless of the compositor
> (about 5-10 LOC)