说明：  在OpenGL环境下，保存窗口客户区的绘制内容为24位BMP位图（可以选择保存位图的大小）；保存8位位图的函数框架也已经搭好。
(In OpenGL environment, the preservation of the window client area for drawing the contents of 24 BMP bitmap (you can choose to save the size of the bitmap) save bitmap 8 has also been a function of the framework搭好.)