Rendering animated hair under dynamic environmental lighting

We present a fast algorithm for the interactive rendering of animated hair under a dynamic lighting environment. Previous methods use spherical radial basis functions (SRBF) for efficient evaluation of the rendering equation for hair [Ren et al. 2010]. However, this method is not suitable for dynamic lighting environments, since it requires a high computational cost to approximate environmental light using SRBFs. We address this problem by using spherical harmonics (SH) to approximate both the transmittance and the environmental light. Since SH functions are orthogonal, the environmental light is efficiently converted into an SH representation. However, to obtain an SH representation of the transmittance for animated hair, we need to compute the transmittance for all directions at each vertex at each frame, which is very time-consuming. Our method reduces the computational cost by using a voxel-based approach to compute the transmittances.