Real-time multiple scattering in participating media with illumination networks

This paper proposes a real-time method to compute multiple scattering in non-homogeneous participating media having general phase functions. The volume represented by a particle system is supposed to be static, but the lights and the camera may move. Lights can be arbitrarily close to the volume and can even be inside. Real-time performance is achieved by reusing light scattering paths that are generated with global line bundles traced in sample directions in a preprocessing phase. For each particle we obtain those other particles which can be seen in one of the sample directions, and their radiances toward the given particle. This information is stored in an illumination network that allows the fast iteration of the volumetric rendering equation. The illumination network can be stored in two-dimensional arrays indexed by the particles and the directions, respectively. Interpreting these two-dimensional arrays as texture maps, the iteration of the scattering steps can be efficiently executed by the graphics hardware, and the illumination can spread over the media in real-time.