I wanted to share my first GZDoom shader project I've been working on.
It's a multi-function shader that supports various effects which can be combined together. They are mostly based on a 3d simplex (perlin) noise function such as texture distortion and tint, in addition to some trippy effects like lerping the hue, saturation, or value.
I've exposed all the uniforms to ZScript and also hooked them up to CVars to make it easy to tweak these parameters at runtime. I added a description of what these CVars do to the README.
Here are some screencaps showing some of the different effects:
Perlin-based texture distortion - the distortion factor, time scale, and 2d noise scale is adjustable.

Perlin-based subtractive pattern and tint - combined with distortion I think this might make a pretty good shader for being inside a fluid, like swimming in water/nukage. I know it's not the first one to do this but I do like the naturalistic look of the perlin noise.

Animated shifting of hue, saturation, and value -

My math for animating these properties is just in zscript so should be easy to modify. Currently you can toggle the animation of H, S & V separately.
Thanks to Major Cooke, I grabbed his distortion shader to figure out the boilerplate I needed to get all of this hooked up.
Feel free to use this for your own mods, etc as I've released it under an MIT-style license. The code is here: https://github.com/fadookie/gzdoom-shaders - you can load it as a file in unpacked pk3 format. I also uploaded a pk3.
I would appreciate a credit if you use it (not required by license though)! Also let me know if you have any feature requests, if I have time I will look into it. I am not a shader expert but I am trying to learn and improve my skills!