A practical and controllable hair and fur model for production path tracing

We present an energy-conserving fiber shading model for hair and fur that is efficient enough for path tracing. Our model adopts a near-field formulation to avoid the expensive integral across the fiber, accounts for all high order internal reflection events with a single lobe, and proposes a novel, closed-form distribution for azimuthal roughness based on the logistic distribution. Additionally, we derive, through simulation, a parameterization that relates intuitive user controls such as multiple-scattering albedo and isotropic cylinder roughness to the underlying physical parameters.