Interactive hair rendering and appearance editing under environment lighting

We present an interactive algorithm for hair rendering and appearance editing under complex environment lighting represented as spherical radial basis functions (SRBFs). Our main contribution is to derive a compact 1D circular Gaussian representation that can accurately model the hair scattering function introduced by [Marschner et al. 2003]. The primary benefit of this representation is that it enables us to evaluate, at run-time, closed-form integrals of the scattering function with each SRBF light, resulting in efficient computation of both single and multiple scatterings. In contrast to previous work, our algorithm computes the rendering integrals entirely on the fly and does not depend on expensive pre-computation. Thus we allow the user to dynamically change the hair scattering parameters, which can vary spatially. Analyses show that our 1D circular Gaussian representation is both accurate and concise. In addition, our algorithm incorporates the eccentricity of the hair. We implement our algorithm on the GPU, achieving interactive hair rendering and simultaneous appearance editing under complex environment maps for the first time.