VoxLOD: Interactive ray tracing of massive models with indirect lighting using voxels

Just encountered an impressive video of a technology named VoxLOD on Youtube today:

http://www.youtube.com/watch?v=1IwtKLtYc9M

As the name aptly implies, VoxLOD uses a voxel-based LOD scheme to smoothly stream in and visualize the geometry of the massive model. The first part of the video shows direct lighting only (primary and shadow rays), while the second half is much more interesting and demonstrates real-time one bounce diffuse indirect lighting (filtered Monte Carlo GI). From the paper "Interactive ray tracing of large models using voxel hierarchies":

"We cast one shadow ray per primary or diffuse ray, and two random diffuse rays per primary ray. The diffuse rays are used to compute both one bounce of indirect irradiance and environment irradiance, which are processed with a bilateral filter [TM98] to eliminate noise."

From an earlier post on the author's blog:

"There are two light sources: a point light (the Sun) and a hemispherical one (the sky). I use Monte Carlo integration to compute the GI with one bounce of indirect lighting. Nothing is precomputed (except the massive model data structure of course).

I trace only two GI rays per pixel, and therefore, the resulting image must be heavily filtered in order to eliminate the extreme noise. While all the ray tracing is done on the CPU, the noise filter runs on the GPU and is implemented in CUDA. Since diffuse indirect lighting is quite low frequency, it is adequate to use low LODs for the GI rays."

Another interesting tidbit from the paper:

"By using LOD voxels, significantly higher frame rates can be achieved, with minimal loss of image quality, because ray traversals are less deep, memory accesses are more coherent, and intersections with voxels are free, contrary to triangles (the voxel fills its parent node, therefore, the intersection is equal to the already computed intersection with the node). Furthermore, the LOD framework can also reduce the amount of aliasing artifacts, especially in case of highly tessellated models"

The quality of the indirect lighting looks pretty amazing for just 2 (filtered) random samples per pixel and is completely noise-free, as can be seen in this picture from the paper

All the ray tracing is currently CPU based (the GI algorithm runs at 1-2 fps on a quad core cpu), but it would probably run in real-time at much higher framerates when implemented entirely on the GPU.

Brigade 2 Blowout!

Jacco Bikker, one of the Brigade developers, posted some updates about the Brigade 2 path tracer:

- there is a new downloadable demo showing off the Blinn shader (Fermi only). I haven't been able to test it yet, but the screenshot looks sweet!

- a brand new video of the Reflect game using Brigade 2 running on 2 GTX 470 GPUs, which demonstrates some dramatic lighting effects and very low noise levels (for a real-time path traced interior scene)

All can be seen and downloaded from here: http://igad.nhtv.nl/~bikker/

There should also be a playable Reflect demo up by tomorrow!

GigaVoxels thesis online

Cyril Crassin has just posted his entire PhD thesis on GigaVoxels, the sparse voxel octree raycasting technology which supports efficient depth-of-field, soft shadows, animated voxel objects and indirect lighting at

http://blog.icare3d.org/2012/01/phd-thesis-gigavoxels.html

There are over 200 pages of voxel raytracing goodies :)

Real-time path traced Sponza fly-through on 3 GPUs!

I've sent the executable of the teapot in Sponza scene to a friend, szczyglo74 on Youtube, who has a much more powerful rig than my own (a PC with 3 GPUs: 1 GTX 590 (dual gpu card) + 1 GTX 460)  and who made some very cool real-time videos of the sponza scene. Many thanks szczyglo!

The maximum path depth in each of these videos is 4 (= 3 bounces max):

32 spp per frame (480x360, 1/4th render resolution, 8 fps): 

http://www.youtube.com/watch?v=fVAl-oKAL9I  :awesome video, shows real-time convergence in most parts of the scene

32 spp per frame (640x480, 1/4th render resolution, 4.7 fps): 

http://www.youtube.com/watch?v=OSqfIDHLido

8 spp per frame (480x360, 1/4th render resolution, ~21fps): 

http://www.youtube.com/watch?v=rYsdlDEaMfY

4 spp per frame (640x480, 1/4th render resolution, ~18fps):

http://www.youtube.com/watch?v=lb8SAGCu57k

The above videos clearly show the importance of the number of samples per pixel per frame in indirectly lit areas: despite the low max path depth of 4, it is still possible to discern some details in the corridors in the first two videos (32 spp per frame) during navigation, while the last two videos (8 and 4 spp per frame) are obviously too dark in these regions, but clear up very fast with a stationary camera. Note that these tests were made with a kernel that is not optimized for indirect lighting (no multiple importance sampling is used here). 

I'm quite happy with the sense of photorealism in these videos, especially when you consider that this is just brute force path tracing (no caching, filtering or interpolation yet nor anything like image reconstruction, adaptive sampling, importance sampling, bidirectional pt, eye path reprojection, ... which are all interesting approaches). A textured version of Sponza will probably further increase the realism, which is something I will try in a next test.  

Utah Teapot in Sponza continued

I've managed to get the "teapot in Sponza" scene to render slightly faster by treating all objects in the scene as static.

Youtube videos (rendered on a GeForce GTS 450):

http://www.youtube.com/watch?v=Rs5Tq8tzp2E (8 spp per frame)

http://www.youtube.com/watch?v=OmTtsFfH_mw (8 spp per frame)

Optix 2.5 released

A few days ago, Nvidia has released OptiX SDK 2.5 RC1 which stands out compared to prior releases due to a number of major improvements:

- out-of-core GPU ray tracing: scenes can now exceed the amount of available GPU RAM (up to 3 times)

- HLBVH2 support (Garanzha and Pantaleoni): replaces the previous LBVH builder and is able to build the BVH acceleration structure on the GPU at a fraction of the time it would take a CPU, which allows for completely dynamic scenes by rebuilding the acceleration structure each frame in real-time (e.g. the HLBVH2 paper reports building times of 10.5 ms on a GTX480 for a model consisting of 1.76M fully dynamic polygons). HLBVH2 traversal speed is said to be comparable to a CPU built BVH

This will greatly benefit real-time GPU path traced games and animations as it not only reduces the BVH build times by several orders of magnitude compared to CPU builders, but also eliminates costly per-frame CPU-to-GPU transfers of the updated BVH (when built on the cpu)

- the SDK path tracing sample is enhanced with multiple importance sampling

Real-time browser based path tracer

While searching the net for ways to improve convergence in dynamic, path traced environments, I stumbled upon this neat web-based path tracer created by Edward Porten:

http://www.openprocessing.org/visuals/?visualID=14228

It uses progressive spatial caching and runs pretty fast despite being CPU-based.

Also check out some other browser-based demos from the same author at http://www.openprocessing.org/portal/?userID=6535

The Sphere flake tracer uses a cool looking frameless rendering technique, roughly comparable to frame averaging.

"Hair Ball" and  "Terrain Ray Marching"  are awesome as well.