“Fast calculation of soft shadow textures using convolution” by Soler and Sillion

  • ©Cyril Soler and François X. Sillion




    Fast calculation of soft shadow textures using convolution



    The calculation of detailed shadows remains one of the most difficult challenges in computer graphics, especially in the case of extended (linear or area) light sources. This paper introduces a new tool for the calculation of shadows cast by extended light sources. Exact shadows are computed in some constrained configurations by using a convolution technique, yielding a fast and accurate solution. Approximate shadows can be computed for general configurations by applying the convolution to a representative “ideal” configuration. We analyze the various sources of approximation in the process and derive a hierarchical, error-driven algorithm for fast shadow calculation in arbitrary configurations using a hierarchy of object clusters. The convolution is performed on images rendered in an offscreen buffer and produces a shadow map used as a texture to modulate the unoccluded illumination. Light sources can have any 3D shape as well as arbitrary emission characteristics, while shadow maps can be applied to groups of objects at once. The method can be employed in a hierarchical radiosity system, or directly as a shadowing technique. We demonstrate results for various scenes, showing that soft shadows can be generated at interactive rates for dynamic environments.


    1. Daniel R. Baum, Holly E. Rushmeier, and James M. Winget. Improving Radiosity Solutions Through the Use of Analytically Determined Form-Factors. Computer Graphics, 23(3):325-334, July 1989. Proceedings SIGGRAPH ’89.
    2. Lynne Shapiro Brotman and Norman I. Badler. Generating soft shadows with a depth buffer algorithm. IEEE Computer Graphics and Applications, 4(10):5-24, Oct. 1984.
    3. Norman Chin and Steven Feiner. Near real-time shadow generation using bsp trees. Computer Graphics, 23(3):99-106, July 1989. Proceedings SIG- GRAPH ’89.
    4. Michael F. Cohen and Donald P. Greenberg. The hemi-cube : A radiosity solution for complex environments. Computer Graphics, 19(3):31-40, July 1985. Proceedings SIGGRAPH ’85.
    5. Robert L. Cook, Thomas Porter, and Loren Carpenter. Distributed Ray Tracing. Computer Graphics, 18(3):137-145, July 1984. Proceedings SIGGRAPH ’84.
    6. Franklin C. Crow. Summed-area tables for texture mapping. Computer Graphics, 18:207-212, July 1984. Proceedings SIGGRAPH ’84.
    7. Paul J. Diefenbach and Norman I. Badler. Multi-pass pipeline rendering: Realism for dynamic environments. In 1997 Symposium on Interactive 3D Graphics. ACM SIGGRAPH, 1997.
    8. George Drettakis and Eugene Fiume. A fast shadow algorithm for area light sources using backprojection. In Proceedings SIGGRAPH ’94, pages 223-230, 1994.
    9. Paul Haeberli and Kurt Akeley. The accumulation buffer: Hardware support for high-quality rendering. Computer Graphics, 24(4):309-318, August 1990. Proceedings SIGGRAPH ’90.
    10. Pat Hanrahan, David Saltzman, and Larry Aupperle. A rapid hierarchical radiosity algorithm. Computer Graphics, 25(4):197-206, August 1991. Proceedings SIGGRAPH ’91.
    11. Paul Heckbert. Discontinuity meshing for radiosity. Third Eurographics Workshop on Rendering, pages 203-226, May 1992.
    12. Paul S. Heckbert. Adaptive radiosity textures for bidirectional ray tracing. Computer Graphics, 24(4):145-154, August 1990. Proceedings SIGGRAPH ’90.
    13. Paul S. Heckbert and Michael Herf. Simulating soft shadows with graphics hardware. Technical Report TR CMU-CS-97-104, Carnegie Mellon University, January 1997. See also the technical sketch ~Fast Soft Shadows~ at SIGGRAPH’96.
    14. Alexander Keller. Instant radiosity. In Proceedings SIGGRAPH ’97, pages 49- 56, 1997.
    15. Daniel Lischinski, Filippo Tampieri, and Donald P. Greenberg. Discontinuity Meshing for Accurate Radiosity. IEEE Computer Graphics and Applications, 12(6):25-39, November 1992.
    16. Nelson Max. Sun and shade, 1988. SIGGRAPH Video Review, ACM. Issue 36, Segment 8. Available from First Priority, P.O. Box 576, Itasca, IL 60143.
    17. Nelson Max. Unified sun and sky illumination for shadows under trees. CVGIP: Graphical Models and Image Processing, 53(3):223-230, May 1991.
    18. Karol Myszkowski and Tosiyasu L. Kunii. Texture mapping as an alternative for meshing during walkthrough animation. In Photorealistic rendering techniques (Proceedings of the Fifth Eurographics Workshop on Rendering), pages 375- 388. Springer-Verlag, June 1994.
    19. Jackie Neider, Tom Davis, and Mason Woo. OpenGL Programming Guide. Addison-Wesley, Reading MA, 1993.
    20. Pierre Poulin and John Amanatides. Shading and shadowing with linear light sources. In Eurographics ’90, pages 377-386. North-Holland, September 1990.
    21. William T. Reeves, David H. Salesin, and Robert L. Cook. Rendering antialiased shadows with depth maps. Computer Graphics, 21(4):283-291, July 1987. Proceedings SIGGRAPH ’87.
    22. Peter Schroder<error>~<error> and Pat Hanrahan. On the Form Factor Between Two Polygons. In Proceedings SIGGRAPH ’93, pages 163-164, 1993.
    23. Mark Segal, Carl Korobkin, Rolf van Widenfelt, Jim Foran, and Paul Haeberli. Fast shadows and lighting effects using texture mapping. Computer Graphics, 18(2):249-252, July 1992.
    24. Fran~ois Sillion and George Drettakis. Feature-Based Control of Visibility Error: A Multiresolution Clustering Algorithm for Global Illumination. In Proceedings SIGGRAPH ’95, pages 145-152, 1995.
    25. Fran~ois Sillion and Claude Puech. Radiosity and Global Illumination. Morgan Kaufmann publishers, San Francisco, 1994.
    26. Cyril Soler and Fran~ois Sillion. Accurate Error Bounds for Multi-Resolution Visibility. In Rendering Techniques ’96 (Proceedings of the Seventh Eurographics Workshop on Rendering), pages 133-142. Springer-Verlag/Wien, 1996.
    27. John R. Wallace, Kells A. Elmquist, and Eric A. Haines. A ray tracing algorithm for progressive radiosity. Computer Graphics, 23(3):315-324, July 1989. Proceedings SIGGRAPH ’89 in Boston.
    28. Leonard R. Wanger, James A. Ferwerda, and Donald P. Greenberg. Perceiving spatial relationships in computer-generated images. IEEE Computer Graphics and Applications, 12(3):44-58, May 1992.
    29. Turner Whitted. An Improved Illumination Model for Shaded Display. Communications of the ACM, 23:343-349, 1980.
    30. Lance Williams. Casting curved shadows on curved surfaces. Computer Graphics, 12(3):270-274, August 1978. Proceedings SIGGRAPH ’78.
    31. Andrew Woo, Pierre Poulin, and Alain Fournier. A survey of shadow algorithms. IEEE Computer Graphics and Applications, 10(6):13-32, Nov. 1990.
    32. Harold R. Zatz. Galerkin radiosity: A higher-order solution method for global illumination. In Proceedings SIGGRAPH ’93, pages 213-220, August 1993.

ACM Digital Library Publication: