A hierarchical shadow volume algorithm

13 years 10 months ago

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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...

Timo Aila, Tomas Akenine-Möller

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