Discontinuous Displacement Mapping for Volume Graphics

Displacement mapping is commonly used for adding surface details to an object. In this paper, we outline a generalized notion of displacement mapping, which allows for unconventional features such as unorthogonal and discontinuous displacement. By lifting the restriction on the geometric properties of the displacement, we can generate many different special effects including peeling, cutting and deforming an object. These types of operations are useful for volumetric objects, where the interior of objects is represented. To address the technical difficulties associated with this generalization, we employed inverse displacement maps in 3D vector space, and devised a collection of techniques, including sampling displaced objects through a proxy geometry, computing displaced surface normals, correcting lighting artifacts at breaking points in a discontinuous displacement map, and creating composite displacement maps from primitive maps on the fly. Through a number of examples of displacement maps, we demonstrate the generality, interactivity and usability of this approach on a set of volumetric objects.