Need help converting a BRP based colour Quantizer postprocessor for URP Unity 6

[vague gulch]

I'm not exactly looking for a true posterizer. But it's like a colour limiting post processing effect. We specify few colours that we need in a colour array and the post processing changes all colours present in the screen to the closest colour we specified in our array of colour pallets.

I found few shaders online, but they all seem to only work in BRP 🙁
https://github.com/oxysoft/RetroSuite3D

^^This above repo has a shader file called RetroPixelMax.cs and its .shader, that is exactly what I'm looking for, but in URP tho.

Just to save your time, here is the code of that file, if you don't want to look into the repo.

https://paste.ofcode.org/MgxucEPQsAcFhPYiKngq5D
Contains RetroPixelMax.cs and RetroPixelMax.shader.

I'm not exactly sure how to approach this, any help in this direction would be appreciated

[nova wyvern]

Here's how to create a custom post process in URP using a fullscreen renderer feature : https://docs.unity3d.com/Packages/com.unity.render-pipelines.universal@14.0/manual/post-processing/post-processing-custom-effect-low-code.html

Since shadergraph doesn't support loops, you can wrap the loop code in a custom function node.