SHADING 3-DIMENSIONAL COMPUTER GENERATED IMAGES

An apparatus for shading 3-dimensional computer generated images representing each object in the image by a set of flat polygons. Vertex data (x, y) is supplied for each vertex of the polygon along with data which defines the orientation of the surface of the polygon. Edge data is computed in edge processors. The edge data is equivalent to data which defines a surface which is perpendicular to a viewpoint and which faces inwardly towards the polygon. For each pixel which is used to view the portion of the image in which the polygon is located, a depth value is derived for each of these surfaces and, when the depth values indicate that the polygon is visible at the pixel, it is shaded accordingly.