An object-oriented approach to shadow generation in computer graphics

摘要

This paper presents an object-oriented shadow generation algorithm for a large number of convex polyhedra (objects) in a 3-D scene. In the past, the shadow volume binary space partitioning (SVBSP) tree algorithm is known to be efficient in a static environment in which the point light source can be changed. However, if a scene consists of many objects and each object consists of many polygons, the time complexity for generating and traversing an SVBSP tree increases rapidly because the SVBSP tree algorithm only deals with polygons which are components of objects. Furthermore, the SVBSP tree algorithm suffers from polygon-splitting problems resulting in a high cost as the number of polygons increases. Our approach is object-oriented in the sense that an object is used as the basic logical unit instead of polygons. In the preprocessing stage the object ordering for shadow generation is determined for all possible light source positions. At the run time, the shadow detection algorithm is executed, and if necessary, shadow fragments are generated. We also present an approach to retrieving, updating, and displaying a 3-D static or dynamic world which consists of a large number of objects.