How can I make a custom mesh class in Unity?

Question

I'm doing something in Unity where I need to specify the position and orientation of vertices with two Vector4s, and they're not just position and normal vectors. I've already written my custom shader and now I need to make mesh objects that can be fed into it.

So how do I make my custom mesh? Should I inherit from the mesh class? Will I still be able to use the normal mesh filter and mesh renderer components or should I replace those too? I am comfortable coding the data structure for my new mesh, the question is interfacing with the Unity rendering pipeline and sending the data to my shader in the right way.

Answer 1

I don't recommend creating a new Mesh class for this.

Instead, send your additional 4D data to the GPU as texture coordinates. Don't let the name fool you - these don't need to have anything to do with textures, they're just streams of arbitrary float data you can use however you want in the shaders.

This might look something like this:

void Add4DMeshData(Mesh source) {
    var vertices = mesh.vertices;
    var normals = mesh.normals;
    var positions = new Vector4[vertices.Length];
    var orientations = new Vector4[vertices.Length];

    for(int i = 0; i < vertices.Length; i++) {
        positions[i] = Get4DPosition(vertices[i]);
        orientations[i] = Get4DOrientation(normals[i]);
    }
 

    mesh.SetUVs(0, positions);
    mesh.SetUVs(1, orientations);
}

Your shader can then read these streams in its input struct...

struct vs_input {
    float4 position    : TEXCOORD0;
    float4 orientation : TEXCOORD1;
    // etc...
};

...and do whatever you need with them, no new Mesh class required.