Real-Time Rendering Algorithm Of Transparent Objects Based On Caustic Volume

In the numerous beautiful light phenomena in nature, those caused by the light transmitting through objects are often fantastic and fascinating. These phenomena, like refraction and caustics, not only attract many researchers'attentions in computer graphics, but also are very difficult to simulate by computers. Limited to the computing ability and storage capacity of graphics hardware, previous researchers have proposed a variety of compromised methods on speed and quality to render these phenomena.In this paper, we firstly explained the physical principles of these beautiful optical phenomena caused by transparent objects. Then we introduced the basic methods currently used for rendering, from those off-line ray-tracing methods that are in pursuit of quality, to those based on traditional rasterization pipeline that are in pursuit of speed. To cover both rendering speed and rendering quality, some researchers raised the method based on caustic volumes to render the transparent objects and related optical phenomena. After a sufficient investigation about traditional caustic volume method, we summarized its shortcomings and proposed an improved algorithm. Through our improved caustic volume method, we utilizes the discrete triangular representation of objects in computers to simplify the interaction between the light beams and the object surfaces to that between the light beams and these triangles. All these simulations are performed based on optical principles. The simplification decreases the amount of calculation directly. On the other hand, the representation of data and related computation used in caustic volume method are suitable for parallel computing, making it possible to accelerate the rendering by using the parallel computation unit in computer. The main research contents of this paper include the following aspects:(1) Fixed the problem that common rendering algorithms of transparent objects only processes the interaction between the light beams and the objects'surface that can be seen from the light source. We obtain the multi maps representation of transparent objects by using the depth peeling technology, to simulate the multiple interactions (including refraction, reflection and grazing) between the light beams and transparent objects. Based on this, the caustic volumes are more accurate for later calculation.(2) Traditional caustic volume methods only apply to the transparent objects whose boundaries can be ignored, such as large-scale water. In this paper, we use technologies, like multi maps representation of the transparent objects and iteration method, to obtain the precious boundary of the interaction between the light beam and transparent object. The triangles on the interaction boundary are then subdivided. This greatly enhances the applicability of caustic volume method.(3) Processed the grazing phenomenon on the interaction boundary between the light beam and the transparent objects, making the caustic volume method able to generate precious shadow (including self-shadow) for the transparent objects. Meanwhile, based on the observation that the caustic volumes have covered both the caustic regions and shadow regions, we unified the radiation estimation for both caustic and shadow with relatively small amount of resources.