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: One is 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, 1) we show that the two-pass z-buffer algorithm causes false shadows in global area due to shortage of z-precision and cannot be used for actual real-time image generators. We 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. 2) We propose a hardware-implementation for the shadow generation. The hardware-implementation is similar to that of texture mapping and reduces the amount of hardware.