The Modeling And Complication Of Volume Rendering Based On RenderMan Specification

Nowadays, the progress of computer graphics and the requirement of animation industry promoted the development of photorealistic rendering. Photorealistic images provide a striking visual effect for audience and good experiences for game player when used for film and game industry. Consequently, photorealistic rendering is gaining increasing importance in the area of special effects, analogue and visual effects.Texture plays a very important role in photorealistic rendering. Main stream commercial Tenderers like VRay, metal ray all have their own texture systems and their rendering technology is already gradually mature especially for that basic texture which is easy to complicate. Except these basic textures, some used to simulate special atmosphere and effects, and have total different ways of rendering. This is what we call volume rendering, the rendering of participating media.Participating media is media among the atmosphere making important interactive with light cross it, for example, fog, smoke, fire and cloud. Light has three kinds of effects when going across participating media. One is absorption, which attenuates the light. One is emission, which emits energy to the light. The last one is scattering, which is divided into in-scattering and out-scattering. In-scattering gathers light from other directions and out-scattering does the opposite thing. Volume rendering is a process of integration for all the volume which is totally different from the rendering of basic texture like plastic, marble and glasses.Because particles are everywhere in participating media, scattering is everywhere. It is impossible to trace every light like common rendering. Usually, we ignore the multiple scattering in volume rendering and actually multiple scattering has very small effects. The core technology is Raymarching when ignoring multiple scattering, and is the important part of my work. Multiple scattering is serious in some cases, like dense clouds under sunshine. In our works, a real-time rendering is proposed which is called Multiple Forward Scattering. This method use phase function which is analogy to BRDF in surface rendering.3D texture is used to make volume texture to analogue the varying density in participating media.2D texture is mapped to the face of objects according to UV coordinate system while 3D texture is mapped everywhere in the volume.3D texture is procedural texturing which is produced by program procedure and have advantages like take up less space in memory.3D texture is flexible because it can be mapped to the color, emission and density channel.Our work is based on 3ds Max "Environment and Effects" module. We modeled and design four fog effects:Fog is used for entire scene and is quick on rendering, volume fog has varying density, volume light is used for all kinds of lights to analogue light beams, and the most important EnvironmentFog is mapped with 3D texture. All the works make up the entire volume rendering.Nevertheless, our work on volume rendering has a big problem of rendering efficiency. Time-consuming is always the main problem of volume rendering. Even successful commercial renderer can’t avoid this problem. Improvement of volume rendering speed may be a valuable research topic in the future.