Method and apparatus for shading graphical images in a data processing

Abstract

The present invention provides an apparatus for displaying an image of an object, as illuminated by a light source, on a display within a computer graphics display system. The image is graphically represented by a mesh of polygons and each polygon within the mesh has a surface defined by a set of vertices. The vertices define the surface of the polygon. The apparatus includes a processor, such as a rasterizer, that is responsive to each set of vertices for rendering each surface within the mesh of polygons in response to ambient lighting to produce a number of initially rendered surfaces within the mesh of polygons. Phong shading is utilized by the present invention. The processor produces a specular highlight contribution for each surface within the mesh of polygons utilizing a halfway vector, pointing from each surface to a direction halfway between a light vector and a vector pointing towards a viewpoint, associated with a vector normal to each surface. Diffuse color contributions are generated within the processor using a light vector from a surface pointing to an illumination source associated with a vector normal to each surface. The specular highlight contribution and the diffuse color contribution for each surface of the initially rendered surfaces are summed to produce finally rendered surfaces within the mesh of polygons. These finally rendered polygons are used to display the image within the computer graphics display system.