Feature: TLAS traversal

[jbikker]

Recently an API was added for building a BVH over a list of AABBs or 'BVHInstances'. It would be nice to have actual traversal of this structure, complete with ray transforms / un-transforms in the leafs, for full TLAS/BLAS traversal. Also needs an example.

[brendan-duncan]

Thank you for the recent TLAS build updates in dev!

I tested it out with the Unity WebGPU path tracer I've been working on, and I have instances now! There's a number of bugs I still need to work out, and I haven't started optimizing performance or memory yet. But as a first pass for instanced BVH meshes, I'm happy it works :-). I'm using BVH_GPU for the TLAS GPU data structure for now.

Here's a test: https://hilarious-toffee-659bf7.netlify.app

It's quite a heavy GPU load currently, and best run with Chrome on Windows or macOS.

I'll put all this up on github after I fix it up a bit more. The ray traverse code shaders are written in HLSL, and get translated to WebGPU with the build pipeline. It's not an official Unity project, just a personal fun project.