Hewlett-Packard Company

Eric A Haines

John R Wallace

Kells A Elmquist

Donald P Greenberg

Kent M Montgomery

Michael F Cohen

Samir L Hanna

Louise M Watson

A method for rendering a three-dimensional image on a computer graphics display device involving the steps of providing a data base defining at least the geometry and reflectivity of light emitters and object in the scene and approximating surfaces of each object in the scene as patches in three dimensional space. Each patch is approximated as one or more elements defined by vertices. A source of irradiated light in the scene is selected and defined as a light source. Then, for each vertex, a form factor representing the fraction of light energy that arrives at the vertex from the source is determined by ray tracing from the vertex to the source. Radiosity is then determined at each vertex based on the form factors determined for each vertex. This process is repeated a selected number of times using a different light source each time. In this manner a plurality of radiosities are determined that collectively indicate the global illumination of the scene. The scene is then displayed based upon these radiosities.

Three dimensional computer graphics employing ray tracing to compute

A method for employing a hierarchical display list in global rendering comprises the steps of traversing the display list and extracting selected primitives and attributes. A bounding volume is defined for selected primitives, and data indicative of the selected primitives, attributes, and bounding volumes are stored in a global database. Global rendering may be performed by either ray tracing or radiosity based upon the data in the global database. In the event that global rendering is performed by radiosity, then a plurality of surface elements for each selected primitive is defined and also stored in the global data base. Shading attribute data for each of the surface elements is defined upon application of a radiosity rendering algorithm to the global database. An alternative display list may be defined from the global database, if desired.

Method for employing a hierarchical display list in global rendering

In an algorithm for deriving radiation images, where view independent radiation calculations are precomputed so that they do not need to be repeated for every view of the same environment. To find the form factors for radiosity techniques, a hemi-cube is constructed around the surface with grid cells defined for all faces on the hemi-cube. All other surfaces in the environment are projected onto the hemi-cube to facilitate the form factor calculations. A novel ray-tracing technique is disclosed where a light buffer in the form of a cube is constructed around each radiation source and grid cells are defined on the faces of the cube. Surfaces in the environment are projected onto the cube and the depths from the source are stored for each grid cell to facilitate shadow testing. Light reflected off of the viewed surface from another surface may be modeled by determining mirror positions of the viewer and the image plane. Instead of storing the depths of surfaces from the viewer or the radiation source, the identity of the polygons in the environment are stored instead to speed up the calculations. Scan conversion hardware is used to accelerate each of these operations. In a graphics pipeline, a feedback path is provided from the image processor to the CPU memory to store the result of the form factor or light buffer pre-computations to speed up the radiosity and ray-tracing calculations by several orders of magnitude.

System for deriving radiation images

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Ithaca, NY, United States of America

Eric A Haines