“Ray Tracing Massive Models using Hierarchically Compressed Geometry” – or: Huh, the things you find when sifting through your old stuff…

Sometimes you just “stumble” over things from the past that you had mostly forgotten about (or “gone into denial over”!?) …. in this case, I was sifting through my back-then-when backups for a copy of some of the large scanned models that I have previously worked with in the past (like the David, Lucy, Atlas, etc). Now my trusted find tool eventually did find some matches on my 12TB backup server, but they were png files in an old paper repo from my TACC account backup … and since I couldn’t immediately place the name of that paper repo I started to get curious, so pulled out that directory, and looked inside. What i found what this here – a “aborted” but almost-finished paper draft:

Now this draft was never actually submitted anywhere, and the style file is wrong, too (it was not submitted to EG06; in fact it wasn’t even written until around 2010 or 2011)… but still, some pretty cool ideas in there for the time – mind that this is over a decade old by now. Some of the ideas that this already talked about (in 2011-ish!):

  • a method of encoding large meshes with only 5-8 bytes per triangle including the BVH
  • using the concept of “quads” (triangle pairs with a shared edge, not necessarily planar) throughout everything, even for regular triangles; which not all ray tracers do yet even today
  • automatica generation of such quads from input triangle meshes
  • hierarchical encoding of both geometry and acceleration structure; basically the same of what we used in our 2021 paper on GPU volume ray tracing compressed unstructured mesh data sets. (And while I’m on that topic: a huge shout-out to Ben Segovia and Manfred Ernst, though, which pioneered this with their way under-appreciated Memory Efficient Ray Tracing with Hierarchical Mesh Quantization paper!)
  • a Quad-BVH with hierarchical encoding of the children relative to their parent node; similar to Carsten’s Compressed-Leaf BVHes paper from 2018
  • first interactive ray tracing of billion-plus sized models on fixed-memory “GPUs”; in this paper I used the “Phi” GPU equivalent that intel had at the time (either KNF or KNC, I really don’t know any more). Using that hardware that “may or may not” have been the reason this paper never got published at the time – but I digress.
  • first SPMD ray tracer / path tracer (RIVL) written with a predecessor/sister-project to what later become ISPC – think an ISPC-based path tracer all running on that KNx architecture.
  • an out of core streaming framework for large data (for the construction), that could even do out of core SAH construction etc, with on-the-fly compressed triangle streams etcpp (I still use that same technology today, just a different implementation).

Sigh. So much cool stuff, and all of that over a decade ago … and really cool results (<10 bytes per triangle, including BVH!) … and then I had completely forgotten about it.

Anyway …. just thought I’d drop that draft here; maybe it’ll inspire somebody to pick up some of these ideas, and do something cool with it – the paper does have some few missing text pieces, and in particular several blank tables with performance data – but the latter is actually a good thing: I didn’t do this intentionally for this blog post (I’m not even sure I still have the latex sources for that paper?!); but I would actually have somehow stripped them, anyway, so it’s good they’re not in there. That doesn’t mean that I didn’t have this running at the time (I did), or that it didn’t perform well (oh yes, it did; absolutely) …. but whoever was going to pick up on these ideas would have to re-implement that all on more modern hardware, anyway (and yes, that would probably just scream on a 3080!).

So; if anybody wants to go for it and re-investigate these ideas: feel free – I won’t do it, because I don’t have the time; but if somebody is looking for a student project, a master’s or bachelor’s thesis, or anything else of that sort, then this might still suit – and might still produce a paper, too, depending on results. And if or when somebody wants to do this on a GPU, and wants to chat about how to best do that – I can still chat, I just won’t write the code, or a new paper.

The things one finds in old accounts, indeed…

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