A shadow generation in real-time computer graphics

This paper proposes a new algorithm for real-time shadow generation of a large gaming area, such as for flight simulators. A shadow generation should be improved for the reality of imagery, but its real-time implementation demands the large amount of hardware and the shortage of precision of fixed point calculation is easy to cause false shadow. Shadow generation algorithms are typified into two types. One is the radiosity method which simulates physical phenomena precisely but slowly. The other is two-pass z-buffer algorithm which stresses rapid calculation with acceptable reality at the cost of correctness. Considering the simplicity and the small amount of calculations, the two-pass z-buffer algorithm has been assumed much more adequate for the implementation of video-rate shadow generation. In this paper, the authors show that the two-pass z-buffer algorithm causes false shadows in global area due to shortage of and precision and cannot be used for actual real-time image generators. They propose an improvement for this disadvantage, which uses polygon numbers assigned in a model database. This method is robust for the shortage of precision of fixed point calculation. They propose a hardware-implementation for the shadow generation. The hardware-implementation is similar to that of texture mapping and reduces the amount of hardware.