利用兼容DC实现图形的保存和再现,实现内幕，滚动窗口的实现，坐标空间，映射方式，设备坐标与逻辑坐标的转换。-Use of compatible DC to achieve the preservation of the graph and reproducibility.Realization of the insider, the scrolling window, coordinate space mapping method, the device coordinates and logi