Splatting With Shadows

In this paper we describe an efficient approach to add shadows to volumetric scenes. The light emitted by the lightsource is properly attenuated by the intervening volumetric structures before it is reflected towards the eye. Both parallel and perspective lightsources can be efficiently and accurately modeled. We use a two-stage splatting approach. In the first stage, a light volume is constructed in O(N3) time, which is about the same time it takes to render a regular image. This light volume stores the volumetric attenuated light arriving at each grid voxel and only needs to be recomputed if the light source is moved. If only diffuse shading is required, then the contribution of any number of lightsources can be stored in the same space. The second stage is formed by the usual rendering pipeline. The only difference is that the light contributions are interpolated from the light volume, instead of using the constant light source intensity. Once the light volume is computed, the actual rendering is only marginally more expensive than in the unshadowed case. The rendered images, however, convey three-dimensional relationships much better and look considerably more realistic, which is clearly needed if volume graphics is to become a mainstream technology.