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.