Looks dope but won't load in latest GZDoom on my mac. Throws this error, funny because I don't think any wad/pk3 has ever thrown an error. Registered on my buddy's machine just to find out!:
Execution could not continue.
Compile Shader 'shaders/Desaturate.fp':
ERROR: 0:4: Invalid call of undeclared identifier 'texture2D'
ERROR: 0:5: Use of undeclared identifier 'screen'
ERROR: 0:7: Use of undeclared identifier 'screen'
ERROR: 0:7: Use of undeclared identifier 'ret'