Papers by Ryusuke Villemin

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Porting RSL to C++

Ryusuke Villemin, Christophe Hery
November 2012

In a modern renderer, relying on recursive ray-tracing, the number of shader calls increases by one or two order of magnitude compared to a straighforward rasterizer dealing only with camera visible objects. Recognizing the potential overhead of RSL parsing in all these shader calls, this report evaluates different C++ pre-compiled ... more

Paper (PDF)

Available as Pixar Technical Memo #12-08

Multiple Importance Sampling for Emissive Effects

Ryusuke Villemin, Christophe Hery
January 2013

We present a method for creating and sampling volumetric light sources directly using the volumetric data, obtaining high quality results with any mirror, glossy or diffuse objects, and integrating with any global illumination framework.

Paper (PDF)

Additional materials: [], []

Published version available as

Available as Pixar Technical Memo #13-02

Physically Based Lighting at Pixar

Christophe Hery, Ryusuke Villemin
July 2013

We recently participated in the Siggraph 2013 Physically Based Shading course, with all notes and documents stored at We provide here direct access to our own chapter, describing the Physically Based System we designed at Pixar (on top of RenderMan) for the movie Monsters University and the short film ... more

Paper (PDF)

A Data-Driven Light Scattering Model for Hair

Leonid Pekelis, Christophe Hery, Ryusuke Villemin, Junyi Ling
May 2015

We present an implementation of the [Marschner et al. 2003] model for importance sampling light reflected from hair. The implemen- tation makes use of a version of Adaptive Importance Sampling (AIS), specialized to fit easily sampled distributions to BCSDFs. Our model is novel among importance sampling implementations in that it ... more

Paper (PDF)

Additional materials: [], []

Available as Pixar Technical Memo #15-02

Art and Technology at Pixar, from Toy Story to Today

Ryusuke Villemin, Christophe Hery, Sonoko Konishi, Takahito Tejima, David Yu
November 2015

Technology has always played an important part in Pixar's movie making process, starting with Toy Story over 20 years ago. This course will take you on a journey through that technical evolution, focusing on how story drove our technical designs and how we utilized new technical advancements to tell more appealing stories. Finally ... more

Paper (PDF)

SIGGRAPH Asia 2015 Course Notes.

Towards Bidirectional Path Tracing at Pixar

Christophe Hery, Ryusuke Villemin, Florian Hecht
July 2016

On Finding Dory and Piper, we were faced with rendering a lot of water, or creatures and sets seen through water and glass. We worked with production artists to give controls for resolving these difficult light transports. We also learned to cheat these effects where appropriate. In these course notes, ... more

Paper (PDF)

Importance Resampling for BSSRDF

Ryusuke Villemin, Christophe Hery, Per Christensen
November 2016

We present a method to improve BSSRDF rendering, which reduces variance due to sampling of the scattering exit point. By using importance resampling, we are able to sample any arbitrary diffusion model, taking into account the geometry of the object at the same time. The new method is trivial to implement ... more

Paper (PDF)

Available as Pixar Technical Memo #16-05

Building an Orthonormal Basis, Revisited

Tom Duff, James Burgess, Per Christensen, Christophe Hery, Andrew Kensler, Max Liani, Ryusuke Villemin
March 2017

Frisvad [2012b] describes a widely-used computational method for augmenting a given single unit vector with two other vectors to produce an orthonormal frame in three dimensions, a useful operation for any physically based renderer. The implementation has a precision problem: as the z component of the input vector approaches -1, floating point cancellation causes ... more

Paper (PDF)

Path Traced Subsurface Scattering using Anisotropic Phase Functions and Non-Exponential Free Flights

Magnus Wrenninge, Ryusuke Villemin, Christophe Hery
July 2017

With the recent move to path tracing for both surface and volume rendering, subsurface scattering has been one of the last light transport modes to rely on empirical or approximate models. Although rendering of subsurface scattering using path tracing is conceptually simple, making the model artist friendly is not. Our new ... more

Paper (PDF)

Additional materials: [PTSSSAlbedoInversionCoeffs.txt]

Available as Pixar Technical Memo #17-07

Pixar's Foundation for Materials

Christophe Hery, Ryusuke Villemin, Junyi Ling
August 2017

Though the philosophies and main principles behind our setups date back to our work on Physically Based Lighting for Monsters University, we present the mental models and more modern features and usages covered by PxrSurface and PxrMarschnerHair.

Paper (PDF)

SIGGRAPH 2017 Course Notes

Caustic Connection Strategies for Bidirectional Path Tracing

Sebastien Speierer, Christophe Hery, Ryusuke Villemin, Wenzel Jakob
March 2018

We propose a new type of sampling strategy for connection-based path tracing algorithms such as bidirectional path tracing. Classical bidirectional path tracing generally exhibits poor performance when sampling light paths involving specular transport (e.g. refraction through dielectrics). We therefore introduce specialized connection strategies that connect through chains of specular events. ... more

Paper (PDF)

Available as Pixar Technical Memo #18-01

Into the Voyd: Teleportation of Light Transport in Incredibles 2

Patrick Coleman, Darwyn Peachey, Tom Nettleship, Ryusuke Villemin, Tobin Jones
August 2018

In Incredibles 2, a character named Voyd has the ability to create portals that connect two locations in space. A particular challenge for this film is the presence of portals in a number of fast-paced action sequences with multiple characters and objects passing through them, causing multiple views of ... more

Paper (PDF)

Additional materials: []

Efficient Unbiased Rendering of Thin Participating Media

Ryusuke Villemin, Magnus Wrenninge, Julian Fong
September 2018

In recent years, path tracing has become the dominant image synthesis technique for production rendering. Unbiased methods for volume intergration have followed, and techniques such as delta tracking, ratio tracking and spectral decomposition tracking are all in active use, and this paper is focused on optimizing the underlying mechanics ... more

Paper (PDF)

Art and Technology at Pixar (SIGGRAPH Asia 2018 Course)

Ryusuke Villemin, Chia-Chi Hu, Sonoko Konishi, Hiroaki Narita, Magnus Wrenninge, David Yu
December 2018

As described by this now famous quote "The art challenges technology, and the technology inspires art", technology has always played an important part in Pixar's movie making process. This course will show how we develop and utilize new technical advancements to tell more appealing stories, using real-world examples from our latest movie Incredibles ... more

Paper (PDF)

SIGGRAPH Asia 2018 Course

Product Importance Sampling of the Volume Rendering Equation using Virtual Density Segments

Magnus Wrenninge, Ryusuke Villemin
January 2020

We propose a new volumetric integration method that combines guiding of candidate point positions and importance resampling. We refer to this as the virtual density segment method (VDS). In particular, we show that this control can be driven by treating invertible PDFs as virtual density sources, which in turn ... more

Paper (PDF)

Available as Pixar Technical Memo #20-01