An Aid to Hidden Surface Removal in Real Time CGI Systems

One of the limiting factors in the development of real-time Computer Generated Image systems for displaying perspective colour scenes is finding a suitable solution to the hidden surface problem. This paper presents a solution to this problem, whereby spatial properties of a three-dimensional 'model' held in the Computer Generated Image system database are utilized in order to minimize hidden surface computations for producing moving perspective scenes. This solution is particularly acceptable to situations involving a fixed model and moving eye point. Often Computer Generated Image systems resort to processing individual surfaces from objects in the model to obtain display priority levels; the solution presented is based upon the use of preprocessed relative priority levels which only require complete objects to be given priority levels thus reducing real-time computation. Once an absolute display priority level for an object is found it will be shown that all surfaces forming that object have known display priority levels. Techniques used to obtain object display priority levels are discussed, together with background information concerning the hidden surface problem.