说明：  1. 实现深度缓存(z-buffer)算法. 输入数据是简单的多边形网格. 2. 实现简单的光线跟踪(Ray-tracing)算法. 输入应包含多边形网格(多面体)和圆.
(1. To achieve the depth buffer (z-buffer) algorithm. Input data is a simple polygon mesh. 2. To achieve a simple ray tracing (Ray-tracing) algorithm. Polygon mesh input should be included (polyhedron), and round.)