Simulating Soft Shadows with Graphics Hardware

This paper describes an algorithm for simulating soft shadows at interactive rates using graphics hardware. On current graphics workstations, the technique can calculate the soft shadows cast by moving, complex objects onto multiple planar surfaces in about a second. In a static, diffuse scene, these high quality shadows can then be displayed at 30 Hz, independent of the number and size of the light sources. For a diffuse scene, the method precomputes a radiance texture that captures the shadows and other brightness variations on each polygon. The texture for each polygon is computed by creating registered projections of the scene onto the polygon from multiple sample points on each light source, and averaging the resulting hard shadow images to compute a soft shadow image. After this precomputation, soft shadows in a static scene can be displayed in real-time with simple texture mapping of the radiance textures. All pixel operations employed by the algorithm are supported in hardware by existing graphics workstations. The technique can be generalized for the simulation of shadows on specular surfaces. This work was supported by NSF Young Investigator award CCR-9357763. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of NSF or the U.S. government.