基于环境遮挡掩码的物理正确柔和阴影绘制算法

摘要

针对物理正确的柔和阴影绘制问题，提出一种使用环境遮挡掩码来实现面光源可见性计算的方法。在绘制前，预先创建一个环境遮挡掩码立方图。在绘制过程中，利用环境遮挡掩码立方图来计算所有与可见性测试四棱锥相交的三角形面片的环境遮挡掩码，并对它们作“与”运算，再通过遮挡距离测试操作即可求出哪些光源采样光线不受遮挡。与蒙特卡洛积分光照计算方法相比，本文方法不但能绘制出物理正确的柔和阴影，而且避免了大量的阴影光线求交测试操作，提高了绘制方程的求解效率。%Focusing on the problem of rendering physically correct soft shadows, a method is proposed which uses occlusion masks to evaluate the visibility of an area light source. Prior to the rendering process, a cube map of ambient occlusion masks is computed. In the rendering process, the cube map is employed to compute the ambient occlusion masks of triangles intersecting with a rectangular pyramid, which is used as the bounding volume for light-source sample rays in the visibility testing. Then the ＂and＂ bitwise operations are carried out on these ambient occlusion masks. Finally, based on the results of the bitwise operations, the blocking-distance testing is further utilized to determine which light-source sample rays are not blocked. Compared with the lighting computation method via Monte Carlo integration, the proposed method can not only render physically correct soft shadows, but also avoid a large number of intersection-testing operations for shadow rays. This advantage can enhance the efficiency in solving the rendering equation.