基于VC++的简单绘图的功能实现，以及当程序窗口发生重绘时，已在窗口绘制的图形会消失无踪，基于这个问题，解决了如何保存已绘制的图形和当窗口发生重绘时如何再现窗口先前内容。-Based on simple drawing VC++ functions, as well as when the program window redraw the graphics have been drawn in the window will disappear without a trace, and sol