Bidirectional point distribution functions for rendering granular media

摘要

The disclosure provides an approach for rendering granular media. According to one aspect of the disclosure, granular media are rendered using bidirectional point scattering distribution functions (BPSDFs). The dimensionality of BPSDFs may be reduced by making certain assumptions, such as random orientations of grains, thereby simplifying light transport for computational efficiency. To generate a BPSDF from a grain, light transport may be precomputed using a Monte Carlo simulation in which photons are shot onto the grain from all directions. The precomputed BPSDF may be used, during rendering, for describing the interactions within grains. When a light ray traced during rendering intersects proxy geometry which replaces grain geometry, the BPSDF may be evaluated to determine light transport. By repeating this process for many light rays in a Monte Carlo simulation, the light propagation through the granular medium may be determined.

主权项

1. A computer-implemented method for rendering a granular medium, comprising:
computing a bidirectional point scattering distribution function (BPSDF) for a single grain or multiple grains of the granular medium, wherein the BPSDF approximates light transport through the single grain or multiple grains, and wherein the BPSDF is derived from a bidirectional surface scattering reflectance distribution function (BSSRDF) through dimensionality-reducing assumptions including an assumption that a plurality of scattering events occur at a center of the single grain or multiple grains; receiving geometry of a scene which includes the granular medium; replacing grains of the granular medium in the scene with proxy geometry representing single grains or groups of grains each having the multiple grains; evaluating the BPSDF to determine light transport through the grains when a traced light ray intersects elements of the proxy geometry representing the grains while rendering the scene; and displaying at least a rendered image of the scene as output on a display device, wherein one or more pixel values of the rendered image are determined, at least in part, based on the evaluating of the BPSDF, wherein the grains are replaced with the proxy geometry and the BPSDF is evaluated either when a camera is zoomed away from the granular medium by at least a predefined amount or when the traced light ray bounces between at least a predefined number of grains of the granular medium.