+1 on PBRT - great textbook, and a full program to boot.

Though they don't use the batching method outlined in the video - it would be interesting to see PBRT modified to do it and compare the resulting efficiency in rendering.

https://github.com/mmp/pbrt-v3/

While batching (and reordering) can have a benefit overall for rendering, it can have a significant (depending on how thoroughly you do it) overhead, and Disney are primarily doing it because they use Ptex to do texturing, instead of the more conventional and more widely used UDIM texture atlasing method for assigning textures to meshes.

Ptex really chokes with non-coherant texture accesses (partly due to the anisotropic filtering method it uses) in terms of thread scalability, so Disney have gone to great lengths to get around this issue. Doing such accurate texture filtering (the same goes for standard UV EWA filtering) is technically better, but is expensive, especially in a path-tracing context, where the whole point is to amortise the cost of shading over all the rays by making each intersection / shading calculation as cheap as possible.

From what I hear there are big downsides to this current implementation: the streaming of batches is pretty much off-line, so time till "first pixel" is significant, and thus you don't get interactive rendering functionality.

Awesome information, thank you very much!

The batching that Disney is doing is a very recent direction and not something that is common - PBRT serves as a straight forward reference implementation.

You are right though that it would be fascinating to see the speed difference. My guess is that it would be substantial.

Even compiling PBRT with Intel C++ instead of Microsoft's C++ compiler gives a %30 - %50 speedup, likely due to reordering instructions for better memory coherency on a granular level (batching rays would give better memory coherency on a very broad level).

It would be interesting to see PBRT re-written with C++ 11/14 idioms, and look at how that affects the execution speed as well.

That's also true, PBRT uses a lot of virtual functions.

Wenzel Jakob's Mitsuba renderer is proper badass.

He is now the co-author on the 3rd Edition. Expecting coverage of the Volumetric Layered Materials and Manifold Exploration. PBRT is only getting better.

The third edition will have an implementation of his paper on layered materials. There won't be anything on Manifold Exploration though, as pbrt has Kelemen style MLT (the third edition extends it with Hachisuka's Multiplexed MLT) instead of Veach style MLT.

They've added other cool new stuff too, such as volumetric path tracing, progressive photon mapping, hair (bezier curves with a Kaijya-Kay BSDF) and a Photon Beam Diffusion BSSRDF.