把整个桌面屏幕截图，保存下来，然后把对话框设置全屏顶层窗口，然后把保存下来的位图，在OnEraseBkgnd中把整个位图贴到对话框上，然后用像皮筋类选择截取范围，看起来就像操作屏幕一样-entire desktop screenshots, preserved and then set up full-screen dialog top window, then the preservation of the bitmap, in which the entire OnEraseBkgnd Bi