Research And Implementation Of Multi-Light Source Accelerating Algorithm For Programmable Shaders

With the level of computer hardware and software rapidly promoting,3D rendering has got quickly popularized and applied in diverse industries, and the quality of rendering also has made great progress following the innovation on technology and the improving of devices. Especially in the film and television industry, the realistic3d rendering pictures have brought incomparable impact to audience. And vigorous support has been conducted in China for3d rendering technology, making3d rendering turn into a new domestic industry power.For the films of large scene level, their scene files often easily have the size of hundreds of megabytes. And taking the requirement of high resolution into account, the image of a frame will frequently need a long time to be rendered. Moreover, in order to simulate the complicated effects of lighting in the real world, commonly a lot of light sources will be set in a scene. So, as a result of running through each light source at each rendering point during the rendering progress, rendering time will accordingly lead a linearly growth as the number of light sources increases. All these have greatly limited the freedom of scene design. In order to improve the rendering efficiency, Designers tend to reduce the number of light sources, seriously affecting the scene performance.To solve the problem of linearly increased rendering time by increasing number of light sources in the scene, the technology of optimizing multiple light sources was produced. Multiple light sources optimization technology reduces the sensitivity of affect to efficiency by the number of light sources, so that the relationship between the number of light sources and the rendering time falls to be sub-linear. More focuses can be paid on how to simulate lighting effects more realistically, without the necessity to worry too much about lowered efficiency by introducing a large number of light sources.This paper compares and analysies several kinds of multiple source optimization al gorithm, and after that regards the Lightcuts algorithm based on hierarchical structure as the one with better acceleration effect and strong universality, which has corresponding supporting programs for complex illumination calculation in realistic rendering, like im plementing the effect of area light, environment mapping, indirect illumination based on virtual point light, and so on. Its basic idea is to cluster a light source into a binary tree according to certain rules, and then to split from the root node of the tree, ending as soon as meeting error threshold scope and obtaining present result, which is called a light cut, as a light source to calculate its illumination, thus reducing the number of light sources to be calculated.In this paper, the platform of research and development is based on the open source rendering engine Pixie under Renderman specification, which is able to read rib files, an d supports writing shaders in the Renderman shading language (RSL).Original Lihgtcut s multiple sources acceleration algorithm does not have corresponding function supporti ng rendering system using programmable shaders. This paper, by integrating Lightcuts a Igorithm and Pixie rendering engine, designs interfaces to support Lightcuts source opti mization algorithm, while ensuring programmable shader’s flexibility. In this paper, according to the characteristics of the engine working process, we optimized the algorithm. And when engine rendered the shadow part, the speed slowed down. So we set shadow area and background luminance two experience parameters to solve this problem. And the parameters work very well in the project.The main work of this paper is integrating rendering engine with the Lightcuts algorithm. So we just support the basic light source, like point light, direct light and spot light. And we need to increase the number of light source categories. In order to further study of the area light support for the Lightcuts algorithm, this paper discusses the improvement way of the area light as a preliminary work.At last, this paper summarizes the research and implementation of the multi-light source optimization, and prospects the next work.