Algorithm Of Soft Shadow Based On Multilayer Shadow Map

With the continuously improvement of computer hardware and the rapid development of computer graphics, the requirements of the final result became higher, especially in the computer animation game design and film production field and so on. Higher quality, faster speed has been pursued continuously by computer graphics researchers. Therefore, people continuously put forward new geometry model, rendering algorithm, in order to get more results in limited conditions by hardware. Shadow as an integral part of reality show, playing a vital role in rendering process, because of this, how to get higher quality shadow performance has been the focus of academic research of computer graphics.There are many different algorithms about the research of shadow, each algorithm has its pertinence. In general divided into umbra and penumbra, Offline rendering and real-time rendering. Limited by the early hardware condition, the research about shadow focus more on the realization of umbra. Along with the computer hardware development and the increasing requirement of quality of the result, research work takes more concentrated in the penumbra, as well as the realization of the transparent object’s shadow. In addition, according to different rendering framework, namely offline rendering and real-time rendering, has a direct impact on the shadow algorithm. In the current hardware conditions and network resources environment, the research for the shadow algorithm gets a new opportunity.Shadow map algorithm has been the basic algorithm of shadow realization, a lot of research work have been done to improve this algorithm. The algorithm does not need to consider scene’s complicated geometry, only store the scene information in the shadow maps. But its weakness is due to the construction of the shadow map only for point light source, so can’t realize penumbra effect, and generated by the resolution of the shadow map the result easy to produce saw effect, the serious distortion. Aiming at these problems, this paper puts forward a kind of multilayer shadow map method:On the one hand, by the construction of multilayer shadow map, reduction and simplify scene to describe the surface light source conditions penumbra performance; On the other hand, realize the shadow effect when light’s ray through the transparent object caused the energy loss. Supported by the project of "massively parallel rendering system", the implementation designed in open source renderer Pixie, and finally the results compared with the business software Maya renderer.This paper mainly content is divided into two parts:1) Construction of multilayer shadow maps:In this paper the experimental platform for the rendering engine is a kind of RenderMan standard designed for offline rendering engine, which pay more attention to render high quality results. This article through modified the value of the visibility during the rendering process to realize of the soft shadow effect, and the calculation of shadow effect has no any influence to other process. This part mainly divided into two steps:The first step to realize soft shadow effect of the opaque objects, in this part through the ray tracing technology to realize the reconstruction of the scene; The second step achieve transparent object soft shadow effect, in this part through the illumination model to simulate the light ray through the transparent object caused the energy loss to simulate the soft shadow effect.2) Optimization of the multilayer shadow maps:This part mainly divided into two steps:In order to minimize the computational time for the shadow map and times between duration, using control compression technology and the quadtree algorithm to rebuild the shadow map for further optimization; In order to minimize the shadow map precision on the impact of the results, puts forward the adaptive algorithm which makes the shadow map adaptive adjust precision in different depth and reduce the sawtooth effect.Based on the original multilayer depth map algorithm to do optimization and exploration, and the results were compared with Maya software, in the premise of guarantee quality as much as possible to reduce the calculation time.