Implementing a Hair Shader for Cycles

Realistic hair or fur is essential when creating a plausible virtual world. In feature animation, this is often used to define the signature look of characters; examples include Pixar’s Brave (Iben et al. 2013), and Walt Disney Animation Studios’ Tangled (Sadeghi et al. 2010; also Ward et al. 2010) and Zootopia (Chiang et al. 2016).

Currently, Cycles has a working hair shader (wiki page, sources), based on Marschner et al. (2003)’s model. Its several assumptions and simplifications make it inaccurate for light colored hair (d’Eon et al. 2011) as well as for most types of fur (Yan et al. 2015). Furthermore, d’Eon et al. (2011) and Khungurn and Marschner (2017) demonstrated it to not be energy conserving.

This project intends to upgrade Cycles’ hair shader to the aforementioned Zootopia shader by Chiang et al. (2016), by porting Pharr (2017)’s implementation. Lukas Stockner has made available a WIP patch , which may also serve as a basis for this work.