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GPU PRO 3 by Wolfgang Engel

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IV
Shadows
In this section, we explore algorithms for generating shadow data. Shadows are
the dark companions of lights and although they can each exist on their own, in
games they should always be together. Achieving good visual results in rendering
shadows is considered a particularly difficult task for graphics programmers.
The first chapter in this section is “Efficient Online Visibility for Shadow
Maps” by Oliver Mattausch, Jiri Bittner, Ari Silvennoinen, Daniel Scherzer, and
Michael Wimmer. The authors introduce an algorithm that makes shadow-map
rendering efficient, and that is particularly useful for shadow mapping in large-
scale outdoor scenes. This algorithm quickly detects and culls the geometry
that does not contribute to shadows in final images. The solution presented by
Mattausch and his coauthors uses camera-view visibility information to create
a mask of potential shadow receivers in the light view, which restricts the area
in which shadow casters have to be rendered. There are four main steps in the
algorithm: determine the shadow receivers, create a mask of shadow receivers,
render shadow casters using the mask for culling, and compute shading. The
authors note that their basic principle is easy to integrate into existing game
engines.
The second chapter in this section is “Depth Rejected Gobo Shadows” by John
White. In this chapter, White describes a technique to provide soft shadows using
a simple texture sample. This approach extends the basic projected gobo texture
concept by removing the incorrect projections on objects closer to the light source.
—Wolfgang Engel
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