Pixar’s Chris Ford on RenderMan Pro Server 16.0

Pixar recently released version 16.0 of RenderMan Pro Server. The release contains some significant developments in ray tracing technology, such as a new ray tracing hider, a radiosity cache, and physically plausible shading, along with advancements in deep compositing support. We talk to RenderMan Business Director Chris Ford about some of these key features of the new release.

fxg: Could you discuss the advantages of the ray-tracing hider, and radiosity cache?

Ford: The ray-tracing hider trades off the advantages of the REYES architecture to achieve a collection of effects that cannot easily be achieved using it otherwise. For this reason adaptive ray-tracing and temporally sampled shading are now quite possible in RenderMan. Arbitrary camera projections are also enabled though they are still a work-in-progress. However, unless these special effects are needed it remains most efficient to use the REYES hider.

fxg: Could you explain what physical plausible shading is?

Ford: Physically plausible shading is a term originally coined by Robert Lewis in a paper entitled “Making shaders more physically plausible” from the Fourth Eurographics Workshop on Rendering, Jun. 1993, pp. 47-62. The basic idea is that shader developers need to pay more attention to the physical laws of energy conservation from which production benefits can be derived analogous to those produced by “linear workflows”. RPS 16.0 provides a set of tools for shader developers who wish to produce physically plausible shaders that run with efficiency. This is where the new integrators and a standard radiosity sample enter the picture. We have implemented MIS (a standard optimization for physically based renderers) so that shader developers do not need to. We have also provided a basic (and growing) collection of building blocks in the form of RSL shaders.

fxg: Deep compositing: as this can seriously increase control to compositing based pipelines over full render/animation solutions – could you please discuss how significant this is for your live action VFX clients vs full animation clients?

Ford: There have always been tradeoffs between compositing and full 3D-based solutions and deeptextures offer still more choices for pipeline designers. Deeptexture compositing pipelines based on our dtex files have existed for years and we have set out to grease the skids to get more deep texture data out of the renderer faster. New features enable multi-camera, multichannel output capabilities and an improved open API for reading and writing our dtex files. Deep compositing is not necessarily a silver bullet but it has certainly found application in both VFX and full animated feature production settings.

fxg: Does Pixar have a position on OpenEXR 2.0 and the FMX OpenEXR 2.0 discussion/announcement – especially as it relates to deep compositing?

Ford: We do not currently have a stated position on the proposed extensions to OpenEXR for deep textures. Clearly WETA is a leading practitioner of deep compositing workflows so if the format works for them, it is likely to work for many studios and users.

fxg: Do the larger file sizes, stereo and OpenEXR extensions affect the performance or is data transfer still trivial compared to computational time of actually rendering when considering a major modern render farm?

Ford: Larger file sizes are certainly a consideration that pipeline designers should evaluate carefully.

fxg: How has the motion blur changed in this release?

Ford: We have added support for more motion-samples, added multisample camera blur, and we now offer controls over whether motion-samples should be re-shaded more than once-per-frame. The increase in realism is quite substantial.

fxg: Could you discuss the commitment the RenderMan team has made to advancing physically correct lighting models?

Ford: We believe our customers want sufficient support from the renderer to implement physically plausible shading and lighting in their pipelines and we believe that we have accomplished this with RPS 16.0. On the other hand there remain lots of applications for physically-IMplausible shading and programmer efficiency, elegance of expression, and high performance are just as important for that purpose. A VFX house needs to be able to offer a wide gamut of looks and RenderMan and RSL is particularly well suited to explore that space.

fxg: When can user get their hands on RPS 16.0?

Ford: RenderMan Pro Server is available right now! We released it on Monday May 9th. Just visit our website for more details: http://renderman.pixar.com