在画图系统中实现圆的生成算法，使圆支持异或模式、实现橡皮筋直线、圆、矩形、实现多边形裁剪、实现基本几何变换（平移）、实现B样条曲线

-In the drawing system to achieve a circle generation algorithm, so that won to support different or models to achieve a rubber band straight, round, rectangular, polygon clipping to achieve and realize the basic geometric transformations (translation), to achieve B-spline curve