Research And Implementation Of Optimization Techniques Based On A Hierarchical Structure For The Multi-Light Source

The rapid development of the three-dimensional animation prompted the rendering technology more and more matures. As we know, the lighting effects is an important aspect in the rendering process. Without light sources, even if very complex scenes can not be seen by people. The scene is more complicated, the more complex the light. So, colorful effects can not be separated from a lot of light sources.There are many examples of multiple light sources in real life. Studies have shown that people prefer to the lighting effect by multiple light sources. In addition, illumination from area light sources, high dynamic range (HDR),environment maps and indirect illumination can demonstrated by many point lights. However, the rendering time increases linearly with the number of lights in virtual3D world. So, we are often forced to use fewer lights or remove unimportant lights to get less time cost. So, the rendering cost can be sublinear with the number of lights after the optimization of many algorithms. Thus, people can focused more with the effect of many lights. So, it is necessary of optimization of many light sources. Not like the other algorithm, this can applied to many scenes.After the analysis and study several multi-light sources algorithms, we choose lightcuts as the research base. Lightcuts is the typical representative algorithm of the optimization techniques based on a hierarchical structure for the multi-light sources. It is widely used and it can applied in demonstrating area light sources, high dynamic range (HDR),environment maps sky light source and indirect illumination. The core idea of the algorithm is using a small amount of light source instead of a large number of light sources and the rendering speed can be accelerated by this. In this paper, we will describe lightcuts in detail.Lightcuts is not perfect. In the process of implementing lightcuts, we find that this algorithm perform well in most case but the penumbra. In this paper, we analysis and study this problem, and we came up with a improved lightcuts, lightcuts with multi-light representative sources. We apply this new algorithm to our project and achieved good results.As our studies and experiments platform is Pixie based Renderman specification and the programmable shaders are not suitable to our optimization algorithm of multi-light sources. So we will discuss how to bulid in this light shaders.In the end of article, we have made a summary of the contents of this paper.