As mentioned above in the directional lights section, the rendering of shadows for directional lights is an approximation that allows us to use a single render to cover a largeish area with shadows.

你也用着色语言作为技术的实现基础来处理阴投射体和接收体的材质来实现更复杂的阴法，比如实现支持自投的深度阴贴图。