本程序完成简单的图形学操作。用鼠标实现画线、画圆、画矩形、多边形等，以及图形的填充、直线和多边形的裁剪

任意多边形的填充,只要输入N个点,然后用鼠标实现.-arbitrary polygon filling, as long as the importation of N points, and then use the mouse to achieve.