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Abstract

Methods for solving shadow problems by solving instances of visibility
problems have long been known and exploited. There are, however,
other potent uses of such a reduction of shadow problems, several of
which we explore in this paper. Specifically, we describe algorithms
that use a resolution--independent, or object--space, visibility
structure for the computation of object--space shadows under point,
linear, and area light sources.

The connection between object--space visibility and shadow computation
is well--known in computer graphics. We show how that fundamental
observation can be recast and generalized within an
object--space visibility structure. The edges in such a structure
contain exactly the information needed to determine shadow edges under
a point light source. Also, the locations along a linear or an area
light source at which visibility changes (termed critical points and
critical lines) provide the necessary information for computing shadow
edges resulting from linear and area light sources. Not only are
instances of all shadow problems thus reduced to visibility problems,
but instances of shadow problems under linear and area light sources
are also reduced to instances of shadow generation under point and
linear light sources, respectively.