A Hierarchical Shadow Volume Algorithm

Aila, Timo; Akenine-Möller, Tomas

A Hierarchical Shadow Volume Algorithm

Files

015-024.pdf (2.35 MB)

Date

2004

Authors

Aila, Timo
Akenine-Möller, Tomas

Publisher

The Eurographics Association

Abstract

The shadow volume algorithm is a popular technique for real-time shadow generation using graphics hardware. Its major disadvantage is that it is inherently fillrate-limited, as the performance is inversely proportional to the area of the projected shadow volumes. We present a new algorithm that reduces the shadow volume rasterization work significantly. With our algorithm, the amount of per-pixel processing becomes proportional to the screenspace length of the visible shadow boundary instead of the projected area. The first stage of the algorithm finds 8×8 pixel tiles, whose 3D bounding boxes are either completely inside or outside the shadow volume. After that, the second stage performs per-pixel computations only for the potential shadow boundary tiles. We outline a twopass implementation, and also describe an efficient single-pass hardware architecture, in which the two stages are separated using a delay stream. The only modification required in applications is a new pair of calls for marking the beginning and end of a shadow volume. In our test scenes, the algorithm processes up to 11.5 times fewer pixels compared to current state-of-the-art methods, while reducing the external video memory bandwidth by a factor of up to 17.1.

        @inproceedings{:10.2312/EGGH/EGGH04/015-024
,
booktitle = {Graphics Hardware
},
editor = {Tomas Akenine-Moeller and Michael McCool
},
title = {{A Hierarchical Shadow Volume Algorithm
}},
author = {Aila, Timo and 
Akenine-Möller, Tomas
},
year = {2004
},
publisher = {The Eurographics Association
},
ISSN = {1727-3471
},
ISBN = {3-905673-15-0
},
DOI = {/10.2312/EGGH/EGGH04/015-024
}
}