Method and apparatus for providing non-photorealistic cartoon outlining within a 3d videographics system

Abstract

In a 3D computer graphics system such as a 3D home video game console, efficient techniques for generating non-photorealistic effects such as cartoon outlining involve generating and displaying border lines at object edges based on contents of a pixel memory. Some techniques use depth (Z) values to determine which pixels are located at object edges, and selectively blend border coloration into those pixels which are then displayed. Object edges are located by comparing pixel depth values with neighboring pixel depth values (e.g., calculating a “distance” value based on the absolute values of the distance(s) between a pixel's depth and depths of neighboring pixels). A desired border line color is blended into the pixel's color value based on the calculated distance value. In one particular example, the distance value is used to calculate a pixel Alpha value which is then used to control the amount of border color that is blended into the pixel color. The Alpha value may be modulated by pixel depth. Other techniques may cause object portions with identification values stored in frame buffer locations normally used to store Alpha values. These ID values can be used to identify object portion intersections for applying a border line color to.