Tuesday, August 18, 2015

FireRays, AMD's OpenCL based high performance ray tracing renderer

Pretty big news for GPU rendering: about 6 years after Nvidia released the source code of their high performance GPU ray tracing kernels and 4 years after Intel released Embree (high performance CPU ray tracing kernels), last week at Siggraph AMD finally released their own GPU rendering framework in the form of FireRays, an OpenCL based ray tracing SDK, first shown in prototype form at Siggraph 2014 by Takahiro Harada (who also conducted research into foveated ray tracing for VR):

The FireRays, SDK can be downloaded from the AMD Developer site: http://developer.amd.com/tools-and-sdks/graphics-development/firepro-sdk/

More details  can be found at http://developer.amd.com/tools-and-sdks/graphics-development/firepro-sdk/firerays-sdk/. The acceleration structure is a BVH with spatial splits and the option to build the BVH with or without the surface area heuristic (SAH). For instances and motion blur, a two level BVH is used, which enables very efficient object transformations (translation, rotation, scaling) at virtually no cost. 

AMD's own graphs show that their OpenCL renderer is roughly 10x faster running on 2 D700 FirePro GPUs than Embree running on the CPU:

There are already a few OpenCL based path tracers available today such as Blender's Cycles engine and LuxRays (even V-Ray RT GPU was OpenCL based at some point), but none of them have been able to challenge their CUDA based GPU rendering brethren. AMD's OpenCL dev tools have historically been lagging behind Nvidia's CUDA SDK tools which made compiling large and complex OpenCL kernels a nightmare (splitting the megakernel in smaller parts was the only option). Hopefully the OpenCL developer tools have gotten a makeover as well with the release of this SDK, but at least I'm happy to see AMD taking GPU ray tracing serious. This move could truly bring superfast GPU rendering to the masses and with the two big GPU vendors in the ray tracing race, there will hopefully be more ray tracing specific hardware improvements in future GPU architectures.

(thanks heaps to CPFUUU for pointing me to this)

UPDATE: Alex Evans from Media Molecule had a great talk at Siggraph 2015 about his research into raymarching signed distance fields for Dreams. Alex Evans is currently probably the biggest innovator in real-time game rendering since John Carmack (especially since Carmack spends all his time on VR now, which is a real shame). Alex's presentation can be downloaded from http://www.mediamolecule.com/blog/article/siggraph_2015 and is well worth reading. It sums up a bunch of approaches to rendering voxels, signed distance fields and global illumination in real-time that ultimately were not as successful as hoped, but they came very close to real-time on the PS4 (and research is still ongoing).

For people interested in the real-world physics of light bouncing, there was also this very impressive video from Karoly Zsolnai about ultra high speed femto-photography cameras able to shoot images at the speed of light, demonstrating how light propagates and is transprorted as an electromagnetic wave through a scene, illuminating objects a fraction of a nanosecond before their mirror image becomes visible: