硬件 Ray Tracing BVH (Bounding Volume Hierarchy) Traversal Optimization: Edge Cases, Failure Modes, and Root-Cause Debugging

[Marcus Smith]

I’ve been chasing frame-time spikes in the 3% low during heavy ray-traced scenes, and my gut says my BVH traversal is the culprit, but I want to hear how you’ve actually debugged this at the hardware level. When you hit a ray-box or ray-triangle intersection stall, how do you isolate whether it’s the traversal depth or a bad node split? I’ve seen cases where a single degenerate triangle or an empty leaf causes the hardware BVH unit to blow past its max traversal depth and fall back to a slow software path—how are you catching those edge cases before they tank your framerates?

On the refit vs. rebuild question specifically: for dynamic scenes with frequent small-object motion, at what threshold do you actually prefer a full rebuild over an in-place refit? I keep seeing overhead creep from refit invalidating the whole hierarchy, but rebuilds eat a massive sync penalty. Anyone have real numbers on where the crossover point is, and how do you handle the failure modes when a refit silently produces an unbalanced tree that wrecks your traversal cost?

"Lag isn’t an excuse, but it definitely wasn’t my fault."

[Author]

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