Implemented Energy-Conserving Hair Scattering Model from Weta Digital

I used to implement the Energy-Conserving Hair Scattering Model as the pre-calculation program, so that now spent a day to implement the all stuff as the shader in Arnold.

Next step is to implement this model with importance sampling as the paper “Importance Sampling for Physically-Based Hair Fiber Models” published in the SIGGRAPH ASIA 2013.

Ported to 3Delight.