A Study On Real-time Shadow Rending

Realistic graphics rending is an important content of graphics technology research. It uses the computer to imitate the real world, bringing realistic visual enjoyment. To achieve realistic graphics, the shadow is obviously an essential part. Because shadow can significantly enhance the graphical realism, and provide important visual cues. Therefore, shadow rendering technology is one of the hot issues in the study of graphics technology.This thesis mainly studies the real-time shadow rendering technology, including the following three aspects:Firstly, the paper introduces the basic theory of shadow rendering. The paper reviews the shadow technology research, and introduces the basic theory of shadow, including identifies the mathematical definition of shadow, derivates the calculation formula of shadow and analyzes the structure and classification of shadow. At last the thesis introduces the basic knowledge of GPU programming, including GPU development history, rending pipeline and shading language.Secondly, the paper analyzes important shadow algorithms. We analyze two kinds of basic implementation technology of shadow, shadow mapping and shadow volume, and compare their advantages and disadvantages. Then we introduce fake shadow technology, because this is a currently main way of realizing real-time shadow rendering. Percentage-Closer Filter technology is easy to implement and widely used. Variance Shadow Maps, Convolution Shadow Maps and Exponential Shadow Maps, all support per-filtering process which makes they fast, but exist light-linking problem for immaturity of the algorithms. At last, the paper briefly introduces soft shadow technology, including Percentage-Closer Soft Shadows algorithm and back projection algorithm.Thirdly, the paper implements an improved fake soft shadow algorithm. The paper implements Percentage-Closer Filter algorithm, hierarchical shadow map and gradient shadow mapping at first stage. Then the paper proposes the improved algorithm, which is real-time shadow algorithm basing Percentage-Closer filtering kernel. It mainly speeds up at filtering stage by hierarchical shadow map and handles self-shadowing at depth test stage by gradient shadow mapping. It makes up a deficiency of Percentage-Closer Filter algorithm and handles the forming of self-shadowing. Then trough algorithm designing, the paper implements the improved algorithm. Through experimental comparison, we find that the improved fake soft shadow algorithm achieves good performance at rending speed, rending quality and stability.