Shader for inverting colors

clewis · 4 March 2018 12:01

I’m looking for a way to invert colors in Retroarch. I think it may be possible with Color Mangler, but I would need some help figuring out how to use it. Is there any shader that can invert colors?

I’m running Retroarch in an arcade cabinet through a CRT monitor with negative video. There is a switch on the chassis to invert the video, but I am tired of switching it back every time I put an original PCB back in.

As I read that back it sounds crazy, but the switch is really hard to get at… I have to use a stick!

Thanks either way.

Monroe88 · 5 March 2018 00:34

The simplest way to invert colors is to output 1.0 minus the colors of the input texture.

gist.github.com

https://gist.github.com/Monroe88/515c970aa51e93e98f3ce6e0a1ffda78

color-inversion.glsl

/*
    Color inversion shader
*/

#if defined(VERTEX)

#if __VERSION__ >= 130
#define COMPAT_VARYING out
#define COMPAT_ATTRIBUTE in
#define COMPAT_TEXTURE texture

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clewis · 5 March 2018 03:53

@Monroe88

Thank you for this! I will post some pictures after I give it a try.

clewis · 12 March 2018 03:36

@Monroe88

I had some time to try out this shader today and it works perfectly! It’s tough to take pictures of a CRT, but here are a few quick phone pics…

Before:

After:

So if anyone is using a Nintendo arcade monitor with Retroarch, this will save you from having to invert the video. Thanks once again for your help with this!