Fast rendering of arbitrary distributed volume densities

In recent years a number of techniques have been developed for rendering volume effects (haze, fog, smoke,clouds,etc.).These techniques are either time consuming (ray-tracing, radiosity) or do not account for arbitrary density distributions. In this paper we briefly analyze the physics of illuminations of volumes and we propose several simplifications suitable for computer graphics practice. In particular, we present a method for rendering arbitrary distributions by means of projective polygonal rendering and solid texturing techniques in approximately the time needed for a usual polygonal object. The proposed method provides good results in a fraction of the computing time required for approaches like ray-tracing or radiosity. Solid texturing is used to define the density distribution and a point-sampling Monte-Carlo method with user-adjustable accuracy to evaluate the illumination model along the path through the volume. Thus, a trade-off between computing time and picture quality ex ists. With this technique one can move through or around the volume and to place objects and/or light sources in the volume. By means of rendering methods like shadowing polyhedra, objects can cast shadows on the volume and/or the volume can shadow the ground.