创建memdc内存缓冲区，简明演示双缓冲方式实现无闪烁绘，功能很简单-Create memdc memory buffer, concise presentation double buffer to achieve flicker-free drawing, functionality is very simple

屏幕抓屏的实现文件,vc++代码实现。采用MemDc方式-File screen, vc++ code. Using MemDc method