层次结构辐射度渲染中的可见性测试

在辐射度渲染等整体光照模型中，可见性测试是影响整体性能的关键，为了获得较好的可见性测试效果，在光线投射方法基础上，对可见性测试方法做了如下两方面的优化，一方面引入Shaft Culling算法，作首轮筛选，以提高线投射的效率，另一方面，在可见性测试和自适应分割时，进行基于可见性的分割，以保证只有完全可见和完全不可见两种情况，这两方面优化都被引入到层次结构辐射度渲染的实现中，实验结果表明，改进过的可见性测试，不仅减少了计算量和误差，还保证了阴影边界的质量。

Visibility Test in Hierarchical Radiosity with Clustering

In radiosity and other global Illumination algorithm, visibility test is the key component, which dominates the performance of algorithm. It consumes much time and memory. So our goal is to reduce the time spent in visibility test and improve the performance of the shadow. This paper introduces an optimized algorithm to reach this goal. The most popular method to test visibility is ray casting. Based on the theory of ray casting, two ways are used to improve the performance. First, the Shaft culling algorithm was introduced to improve the efficiency of ray casting. It preprocesses to cut off a majority of objects that need not to be test. This algorithm is very useful for decreasing the computation of ray casting. Second, do visibility based meshing. It makes a difference between full visibility, full occlusion and partial occlusion. This guarantees partial occlusion is almost eliminated. This work not only decreases the computation cost and error, but also ensures the quality of the shadow boundary. The two ways are used in the implementation of HRC. Results show the new method is more efficient and the shadow created is very smooth.