ShaderLab | tool designed for cross compiling unity shader | iOS library

I have been trying to achieve this effect from Tim-C (which all seems to be outdated, even the fixes posted in the comments) with ShaderGraph (Unity 2019.3.0f3), but as far as I know you can't do that within ShaderGraph, so after looking at this page on the ShaderLab documentation I came up with the following shaders that use a shader graph I made.

Using this shader displays the shader graph completely fine:

I have two shaders, UnlitRGBA and TransparentNoOverlap. They are as follows:

UnlitRGBA.shaderlab

Update

The main question is: How can I pass the world space vertex positions of the triangle to the surface shader in a Unity shader. As mentioned in a comment it might be possible to pass them from a geometry shader. But I read somewhere that implementing a custom geometry shader overwrites Unitys logic to calculate shadows etc. I would add the triangle information in the Input structure. But before I change my mesh generation logic for it I would like to know if this is feasible. For this solution the vertex positions of the triangle must be constant for every pixel in a triangle and not be interpolated.

This is the original question:

I am writing a surface shader for a triangle mesh. I set a custom vertex attribute with a texture id to every vertex. Now I want the surface shader to apply the texture as seen in the following image. (Note that each color is representing a texture)

In the surface shader I need the 3 vertices that define the triangle and their texture ids. Furthermore I need to position of the pixel I am drawing.

1. If all texture ids are the same I pick this texture for all pixels.
2. If one or two texture ids differ I calculate the pixels distance to the triangle vertices and pick the texture like seen in the next image:

The surface shader needs to be aware of the pixels triangle. With this logic I should get the shading I am looking for. I am creating my mesh programmatically so I can add the triangle vertices and their texture ids as vertex attributes and pass it to the surface shader.

But I am not sure if this is feasible with how surface/vertex shaders work. Is there a relationship between the vertex and the pixel to get my custom triangle information from? Is there a better way of doing this?

I am using Unitys ShaderLab for my shaders.

I ported a Plasma ball shader from Shadertoy to Unity as Image Effect which is attached to the camera. It works fine on the Editor and Windows standalone build. It does not work on Android devices. It is flashing blue and black images on Android.

Here is what it looks like in Unity Editor and Windows Build:

Here is what it looks like on Android:

The ported Shader code:

I'm rather new to shaderlab with unity. I am trying to distort the vertices so that they are push backwards and towards the camera almost like looking at the camera from a 45 degree angle. I am replicating an effect from a game for fun. This is the code used for the effect

ive tried implenting the code into a shader script like so: