说明：  能简单的实现三维模型的阴影投射和阴影的接收，功能简单，还需进一步完善。注：本例子是利用osg3.0库，在VS的环境下实现的
(Simple three-dimensional model of the shadow casting and shadow receiving simple, functional, needs further improvement. Note: This example is the use of osg3.0 library in the VS environment.)