屏幕截图：建立一个屏幕的设备上下文，根据屏幕上下文创建一个内存位置，最后将内存位图数据读入到文件实现屏幕截图操作。-Screenshots: set up a screen device context, according to the context of the screen to create a memory location, and finally the memory bitmap data into the document read realize screenshot of