there was some discussions recently about displacement map, and i found a
paper that seems interesting on the web :

Ray-Tracing Procedural Displacement Shaders
Wolfgang Heidrich and Hans-Peter Seidel

Abstract
Displacement maps and procedural displacement shaders are a widely used
approach of specifying geometric detail and increasing the visual complexity
of a scene. While it is relatively straightforward to handle displacement
shaders in pipeline based rendering systems such as the Reyes-architecture,
it is much harder to efficiently integrate displacement-mapped surfaces in
ray-tracers. Many commercial ray-tracers tessellate the surface into a
multitude of small triangles. This introduces a series of problems such as
excessive memory consumption and possibly undetected surface detail. In this
paper we describe a novel way of ray-tracing procedural displacement shaders
directly, that is, without introducing intermediate geometry. Affine
arithmetic is used to compute bounding boxes for the shader over any range
in the parameter domain. The method is comparable to the direct ray-tracing

methods

http://www.dgp.toronto.edu/gi/gi98/papers/111/111.html

M

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