Modeling And Implementation Of Light Source For Photorealistic Rendering Based On RenderMan

Digital animation and film industry is the strategic emerging industry that our country is striving to develop in recent years. And, computer3D rendering technology is playing a more and more important role in this field. Rendering refers to the progress of generating pixel-level images from digital models. The progress from models to images needs the computing of the rendering target’s colors, which is called shading. While, illumination is the foundation of shading. Since the1980s when the programmable shaders came up, programmable shaders quickly became the high reliability and high expansion tools to depict the objects’material properties in the field of computer graphics. And, the light sources should also be depicted as programmable shaders.Many3D designer apply Autodesk Maya, the world’s top3D animation software, which is produced by Autodesk inc. in the United States, providing perfect function of3D modeling, animation, special effects and fast rendering. One rendering system commonly first tries to support Maya. But the interpretations of Maya light sources by diverse products for rendering often differ. For these reasons, it’s necessary to accurately support Maya light sources and to obtain the shaders accessible for rendering.In this paper, light sources shaders are modeled, designed and implemented, oriented to the demand of the project Research and Application of Photorealistic Animation Rendering System, based on RenderMan. It satisfied well the need of Maya scenes’rendering, combined with the renderer Bleman developed by the research group.The main content of this paper’s work is divided into two parts:One is the modeling of light sources. The illumination in the real world is very complex. It is affected by multiple factors, such as the physical properties of light sources, diverse factors of environment or air, the spatial relationships at the scene, and so on. The former two of these factors may be unified as the attributes of the light sources in a scene. By adjusting them, complex illumination can be simulated. The modeling of light source formulates the task of light sources’ model, as well as integrates all the impact by attributes and the progress of light transmitting or occlusion. Each point in the scene can obtain the color contribution from lighting through the model. The light source model should not only follow the rules of science, but also meet the expectation by users being used to classic design software Maya. So, Lamber cosine law, Hermite interpolation, and some empirical data and formula in other rendering products such as3Delight are applied to modeling.The other one is the design and implementation of shaders. The implementation of shaders from the model adopts RenderMan’s RSL(RenderMan shading language), with which the.sl files are programming. These programming shaders are compiled to executable shaders by RenderMan standard compiler. Test plentiful scenes and revise shaders. The C++programming rendering platform system takes use of Maya API to export necessary attributes into shaders, so that these shaders can directly support Maya users’setting. Instead of directly exporting RSL codes, the macro definition of these codes is writed into the files to simplify the shaders. They are read from head files when.sl files are being compiled. After the compiling, the.sdr shaders get ready for the later calling by the renderer.The work of this paper supplyes the independent research and development of photorealistic rendering system by our group, as an important part of shader library for rendering.