Rendering Shadows On Translucent Objects

Shadow rendering is one of the important parts of Computer Graphics. Shadows always can help us understand the information in the three-dimensional scene better. The traditional shadow algorithms do not consider about the material of shadow receiver, but use the same method to compute all the shadows on different objects in a scene. But compared with opaque objects, translucent objects have sub-surface scattering optical property. The property causes the different shadow on opaque objects and translucent objects. In real world, there are many translucent objects, like milk, candle, marble, and so on. So rendering shadows on translucent objects is an important issue in photorealistic rendering.For now, there are many different shadow algorithms. However there are little algorithms to apply to rendering real-time shadows on translucent objects. This thesis analyses the sub-surface scattering optical property of translucent objects, presents an algorithm of rendering real-time shadows on translucent objects based on Shadow Mapping. Experimental result shows that our method can render the shadows on translucent objects with more realistic appearance in real-time.The main research and contributions of this thesis include the following aspects:(1) Presents an algorithm of rendering real-time shadows on translucentobjects in figure space, considering the sub-surface scattering optical property of translucent objects. We can get more photorealistic shadow and guarantee the real-time rendering.(2) Brought out there is a Scatter Shadow Region in the shadow area on translucent surface, which is generated because of sub-surface scattering optical property. Scatter Shadow Region is not lightened directly by light sources, but has the light scattered from the inside of the objects. We present the illumination model of scatter shadow region, use the mind of dipole model, and compute the color of the points in scatter region by weight average.(3) Used the random sample method to blur the shadow in the scene. Considering sub-surface scattering optical properties of translucent objects, after getting the shadow map, use the scatter coefficient of translucent objects to determine the scope, then compute the probability value of the target point, then render the scene at last.(4) Implement and test the algorithm presented by this thesis. Comparing the algorithm with the existed algorithms, it can be verified that our algorithm can render better shadows on different objects and the algorithm can be executed in real-time.