I’ve written a compute shader that generates mesh geometry. Right now its output is a buffer of point data representing triangles. In the current version, each face-vertex just uses the normal of its face which creates a faceted look. I want to be able to calculate smoothed normals for each vertex.
To do this, I need to find the smoothed normal of a vertex, which is the weighted average normal of all the faces that share that vertex. This requires me to uniquely identify each vertex. Luckily I do have a method that gives me an id for each vertex based on where it appears in a grid. However, I then need to map this id to an index. So I need some sort of hash table which allocates a new index when it encounters a new id or returns the already allocated id if it has already been encountered.
Basically, I need a multithread safe function int allocate_index(int hash) that will be fed inputs like
56, 42, 56, 10, 42, 42, 10, 13, 56, 10
and should return
0, 1, 0, 2, 1, 1, 2, 3, 0, 2
over several calls from several different threads. Basically I’m turning a sequence of hash ids into a buffer of indexes.
To do this, I need to lock my hash-to-index function. As far as I can tell, GLSL compute shaders only let you do atomic operations on single lines. I’m also not sure if the barrier() method could be used to create something like a mutex here.
Anyhow, this problem is also very similar to trying to create a compute shader function that calculates an index buffer for a set of unindexed triangles. Fairly straight forward to do on the CPU, but I’m having trouble trying to think of a way to do it in a compute shader.