Real-time multiple scattering using light propagation volumes

This paper introduces a new GPU-based, real-time method for rendering volumetric lighting effects produced by scattering in a participating medium. The method includes support for indirect illumination by scattered light, high-quality single-scattered volumetric shadows, and approximate multiple scattered volumetric lighting effects in isotropic and homogeneous media. The method builds upon an improved propagation scheme for light propagation volumes. This scheme models scattering according to the radiative light transfer equation during propagation. The initial state of the light propagation volumes is based on single-scattered light identified with shadow maps; this allows generation of a high quality initial distribution of radiance. After propagation, the resulting distribution is used as a source of diffuse light during rendering and is also ray marched for volumetric effects from multiple scattering. Volumetric shadows from single-scattered light are rendered separately. We compare the new method to single-scattered volumetric shadows produced by contemporary techniques, plain light propagation volumes (which this new method extends), and a simple composition thereof.