Stackless MBVH Traversal for CPU, MIC and GPU Ray Tracing

[mpeterson]

On CPU, the fastest practical approach is straight MBVH traversal. For first bounce diffuse rays, Tsakok's MBVH/RS is optimal. I presented a paper with an approach that outperforms both (by ~20%), but it's a complex algorithm:
http://arauna2.ompf2.com/files/cgf_article.pdf

it goes even much faster then this. stay tuned...

[voxelium]

Paper/code or it didn't happen!

I'm also using single-ray MBVH on CPU & MIC, but for me it's better than MBVH/RS even for first bounce rays: http://www.cs.ubbcluj.ro/~afra/publicat ... _mbvh8.pdf

A ~20% speedup sounds perfectly reasonable (what about multi-threaded perf though?), but I would be really surprised if we could improve this by an order of magnitude for incoherent rays.

[voxelium]

My paper can now be downloaded from here: http://cg.iit.bme.hu/~afra/publications ... mbvhsl.pdf

[joedizzle]

This is an excellent paper, I'll use it for my GPU tracer. One thing that I've noted, it seems the pseudo-code for BVH2 might lead to infinite loops for a novice implementer who might use the code as it is. I tested the code for a simple square plane which is made up of 2 triangles, meaning all nodes have same bounding box properties. This scenario will force the ray to intersect both leaf bounding boxes and do necessary intersection test, for a properly defined bvh (one node, 2 leaves i.e. 2n-1 property). As a result using the code in the paper, the ray traversal never enters the second leaf. Analysis of the code points to the problem of the leaf node code below.

Code: Select all

// Leaf node
if (!isInner(nodeId)) {
    ...
}

which should be

Code: Select all

// Leaf node
if (!isInner(nodeId)) {
   // do necessary intersection first
   ...
   
   // update parent and sibling status
   parentId = nid.x;
   siblingId = nid.y;
}

the above modified section of the leaf node code, resolved the issue. After a strenuous week of debugging. Lol

Has anyone encountered the similar problem?

[mpeterson]

again: this is 10 years old crap. go with state of the art -> google is your friend !

[joedizzle]

I will definitely, in my TODO list of latest algorithms, https://github.com/joedizzle/CLTracer (I will properly organize the repository soon).

- But if you're dealing with platforms that have limited capability in dealing with stacks, the latest algorithm that I found, but with limited public available information is... "Efficient stackless hierarchy traversal on GPUs with backtracking in constant time"... http://research.nvidia.com/publication/ ... -hierarchy.

- This is well implemented in "RadeonGPU Raytracer"... https://github.com/GPUOpen-LibrariesAnd ... onRays_SDK. I might implement it once I understand the algorithm.

- The final accelerator to implement for GPU is "GPU Ray Tracing using Irregular Grids" (solves teapot in a stadium problem) - https://graphics.cg.uni-saarland.de/index.php?id=939 which seem to be quite superior.

My previous comment was just a simple identification of a problem that I haven't seen it been discussed anywhere in the internet.