Computer Science Department
School of Computer Science, Carnegie Mellon University


Simulating Soft Shadows with Graphics Hardware

Paul S. Heckbert, Michael Herf

January 1997

An abbreviated version appeared in "Fast Soft Shadows",
Michael Herf and Paul S. Heckbert,
Visual Proceedings, SIGGRAPH 96, August 1996, p. 145.

Keywords: Penumbra, texture mapping, graphics workstation, interaction, real-time, SGI Reality Engine

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.

11 pages

Return to: SCS Technical Report Collection
School of Computer Science homepage

This page maintained by