Raytracing tidbits

Over the past few months I did some smaller scale raytracing experiments, which I shared on Twitter but never documented properly. I am collecting them all in this post for ease of access.

On ray divergence

Raytracing has the potential to introduce large divergence in a wave. Imagine a thread with a shadow ray shooting towards the light hitting a triangle and “stopping” traversal while the one next to it missing it and having to continue traversal of the BVH. Even a single long ray/thread has the potential to hold up the rest of the threads (63 on GCN and 31 on NVidia/RDNA) and prevent the whole wave from retiring and freeing up resources.

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Raytracing tidbits