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Comment by ilaksh | Hacker News Reader

I really want graphics hardware that does path tracing. Like if I could feed that material test json into some graphics card or something and get realtime results. That would be bad ass.

The reason I know something like this is doable with enough engineering is the Brigade Engine demos.

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It looks like voxel cone tracing is becoming popular at the moment. Both approaches have the disadvantage that you need to keep the entire scene in video memory, however with VCT that memory usage is bounded by the voxel resolution and integration over large solid angles is very cheap and has no aliasing. It's probably also a disadvantage of GPU path tracing that it makes little use of the features that graphics cards provide.

Here's an article on a voxel raytracer focused on realtime operation: https://directtovideo.wordpress.com/2013/05/08/real-time-ray...

And here's a video of the raytracer discussed in the above link: https://www.youtube.com/watch?v=i8hSZGTXTx8

I'm not sure how well this renderer handles arbitrary scenes through. Pieces of broken glass are very suitable for GPU raytracing, because rendering them is not a "branchy" task since there is no scattering, only definite reflection/refraction. The reflections also make it look like there were a lot more triangles. With Monte Carlo sampling you need 4x samples for .5x error, which means that a lot of samples are needed for scattered indirect illumination in a typical scene (I think in the order of 100 to 1000). In VCT you only need 7-13 samples but a lot of preprocessing.

The author mentions that he chose reflective materials for exactly that reason.

Realtime renderers still struggle with things like Monte Carlo.

I was on a team that experimented with building GPU pathtracers at Pixar. We had some interesting results: https://www.youtube.com/watch?v=LACmRpMYOak

That's a cool project. But that's a software pathtracer running on CUDA cores rather than a "hardware pathtracer" (whereas the pathtracing would be hard-coded into optimized hardware), right?

I think the largest hurdle is designing a GPU that can do both ray tracing and the current system without being absurdly expensive.

You need to be able to handle existing games as well as the next generation to sell the hardware.

Have you heard of PowerVR's raytracing chip? http://www.imgtec.com/powervr/raytracing.asp

Maybe you could use one of more Field-programmable gate arrays.

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