我自己写的代码 可能比较简单 我实现了模拟图层的功能

				///////////////////////////////////////////////////////////
				//  Arc.h
				//  Implementation of the Class Arc
				//  Created on:      18-二月-2009 17:17:24
				//  Original author: pangyj
				///////////////////////////////////////////////////////////
				
				#if !defined(EA_338448F3_A260_465f_B227_7E6BD48A3DC0__INCLUDED_)
				#define EA_338448F3_A260_465f_B227_7E6BD48A3DC0__INCLUDED_
				
				#include "Point2D.h"
				#include "ErrorStatus.h"
				#include "GeometryPrimitive.h"
				
				class Arc : public GeometryPrimitive
				{
				
				public:
					Arc();
					Arc(Point2D pt,double r,double ds,double de);
					virtual ~Arc();
				
					const Point2D & center()const;
					ErrorStatus center(Point2D & pt);
					ErrorStatus endAngle(double agle);
					double endAngle()const;
					double radius()const;
					ErrorStatus radius(double agle);
					virtual ErrorStatus read(fstream& f);
					double startAngle()const;
					ErrorStatus startAngle(double agle);
					virtual ErrorStatus write(fstream& f);
					virtual void list()const;
				
				private:
					Point2D centerPt;
					double dEndAngle;
					double dRadius;
					double dStartAngle;
				
				};
				#endif // !defined(EA_338448F3_A260_465f_B227_7E6BD48A3DC0__INCLUDED_)