[glut]

What sort of raytracing are they using?

Are they going all the way to an unbiased global light transport algorithm (like LuxRender) or just using basic raytracing (like PovRay)?

Are they using an existing renderer? If not, are they releasing their own like they did with RenderMan?

Are they rendering with CPUs or with GPUs?

How much time per frame does it take them with how many cores of what sort?

[joshuak]

Interesting questions. I don't have the answers, but I can say that I can't imagine that Pixar would ever 'go all the way' to an 'unbiased' GI renderer.

Our entire function in the filmmaking business is to tell a story visually, and for that you need complete control and directability of the image. This is the opposite goal of unbiased renderers. Nevertheless more tools in the tool box is always good.

[berkut]

Unbiased actually isn't slow - Arnold has proved this - what's slow is using hundreds of bounces per path and bi-directional path tracing (like Maxwell, Indigo, LuxRender) which takes a lot longer.

Biased generally means it's interpolated with a point or irradiance cache.

[berkut]

They're using uni-directional path tracing - if they're using PRMan 17 (Which I think they were), it'll probably be unbiased like with Arnold. So it's unbiased, but unidirectional, unlike LuxRender's MLT (two-way path tracing).

PRMan 17's a fairly good raytracer now (Arnold was giving PRMan a bit of a kicking in this department over the last two years).

All on the CPU - there's no way GPUs can cope with the size of textures and geometry feature films need to cope with (up to 200 GB of textures and Geometry in some of the complicated scenes) - there's no way that's fitting on a GPU.

I don't know what Pixar have, but SPI (who use their own version of Arnold) used to have quad socket i7s, so 64-thread machines with 96 GB of RAM two years ago - some of the more complex frames were taking +30 hours at 2k.

[ginko]

Combining bi-directional path tracing and ray differentals(needed for texture filtering and geometry subdivision) doesn't really work well together at the moment, sadly.

[berkut]

Ray differentials are just two extra rays one pixel up and right of the main ray to give the ray width. It's pretty trivial to keep them up to date with the main ray at surface intersections (it's technically more work, sure), but it's doable, so I don't see a problem with it.

BDPT is more concerned with the surface area of meshes and solid angles of hits, so that the light path vertex weightings can be accurate.

[KaiserPro]

1) http://renderman.pixar.com/view/raytracing-fundamentals 2) Unbiased renderers like Maxwell and arnold very different beasts. Unbiased renderes have only become practical with moore's law. Renderman is so prevalent because its both fast and flexible. Maxwell specifically has a very distinct look. 3) its renderman. They eat their own dog food. 4) CPU, with GPU bits for specialist stuff 5) AAAAAAGGGEESS 24hours a frame in some cases. even more if there is lots of fur/water