关于Arc2D的角度问题

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        用过JAVA 2D中的Arc2D类的就会发现,画出来的圆弧的角度与构造函数中的角度并不一致.通过查看Arc2D的源代码可以发现,Arc2D是这样生成圆弧的:首先使用给定的起始角度与跨越角度生成一个半径为1的标准单位圆弧,然后通过伸缩变换,将其转换为构造函数中指定的椭圆上的圆弧.显然,这样得到圆弧的起始角与跨度角与构造函数中的已经不一样了,除非这个椭圆本来就是个圆,或者其角度为90的倍数.

        既然知道了Arc2D的生成原理,通过简单三角变换,我们很容易通过角度变换使用Arc2D生成我们需要的圆弧.下面的代码就是将圆弧的实际角度转换为Arc2D的参数角度:

java 代码

public   static   double  degreeTranslate( double  width, double  height, double  degree){
      double  radian =Math.toRadians(degree);
      double  trans  =Math.atan2(width*Math.sin(radian),height*Math.cos(radian));
      double  angle =Math.toDegrees(trans);
      return  angle> 0 ?angle: 360 +angle;
 }

 

       下面,我们通过一个完整的程序来显示这段代码的正确性:

java 代码

import  java.awt.*;
import  java.awt.event.*;
import  java.awt.geom.*;
import  javax.swing.*;
/**
*Arc2D中角度变换的测试程序
*@author Eastsun
*@Version 1.0
*/
public   class  ArcT  extends  JFrame  implements  ActionListener,FocusListener{
     public   static   double  degreeTranslate( double  width, double  height, double  degree){
         double  radian =Math.toRadians(degree);
         double  trans  =Math.atan2(width*Math.sin(radian),height*Math.cos(radian));
         double  angle =Math.toDegrees(trans);
         return  angle> 0 ?angle: 360 +angle;
    }

     public   static  Arc2D createArc( double  x, double  y, double  width, double  height, double  start, double  extent, int  type){
         double  nStart =degreeTranslate(width,height,start);
         double  nExtent = 0 ;
         if (extent>= 360 ||extent<=- 360 ) nExtent = 360 ;
         else {
            nExtent =degreeTranslate(width,height,start+extent)-nStart;
             if (extent< 0 &&nExtent> 0 ) nExtent =nExtent - 360 ;
             if (extent> 0 &&nExtent< 0 ) nExtent =nExtent + 360 ;
        }
         return   new  Arc2D.Double(x,y,width,height,nStart,nExtent,type);
    }

     private  Arc2D arcA,arcB;
     private   double  start,extent;
     private  JTextField startField,extentField;
     private  Stroke strokeB = new  BasicStroke( 3 .0f,BasicStroke.CAP_BUTT,BasicStroke.JOIN_MITER, 10 .0f, new   float []{ 5 , 20 , 5 , 10 }, 0 ),
                   strokeA = new  BasicStroke( 3 .0f),
                   strokeX = new  BasicStroke( 1 .0f);

     public  ArcT(){
         super ( "圆弧测试程序" );
        JPanel drawPanel = new  JPanel(){
             public   void  paintComponent(Graphics g){
                 super .paintComponent(g);
                Graphics2D g2 =(Graphics2D)g;
                g2.setPaint(Color.white);
                g2.fillRect( 0 , 0 ,getWidth(),getHeight());
                g2.setPaint(Color.black);
                g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_ON);
                g2.setStroke(strokeA);
                g2.draw(arcA);
                g2.setPaint(Color.red);
                g2.setStroke(strokeB);
                g2.draw(arcB);
                g2.setStroke(strokeX);

                g2.setPaint(Color.black);
                g2.draw( new  Line2D.Double( new  Point( 160 , 120 ),arcA.getStartPoint()));
                g2.draw( new  Line2D.Double( new  Point( 160 , 120 ),arcA.getEndPoint()));

                g2.setPaint(Color.red);
                g2.draw( new  Line2D.Double( new  Point( 160 , 120 ),arcB.getStartPoint()));
                g2.draw( new  Line2D.Double( new  Point( 160 , 120 ),arcB.getEndPoint()));
            }
        };
        drawPanel.setPreferredSize( new  Dimension( 320 , 240 ));
        add(drawPanel,BorderLayout.CENTER);

        JPanel setPanel = new  JPanel();
        setPanel.add( new  JLabel( "起始角度:" ));
        startField = new  JTextField( "0.0" , 6 );
        start = 0 ;
        startField.addActionListener( this );
        startField.addFocusListener( this );
        setPanel.add(startField);

        setPanel.add( new  JLabel( "跨越角度:" ));
        extentField = new  JTextField( "90.0" , 6 );
        extent = 90 ;
        extentField.addActionListener( this );
        extentField.addFocusListener( this );
        setPanel.add(extentField);

        arcA =createArc( 20 , 15 , 280 , 210 ,start,extent,Arc2D.OPEN);
        arcB = new  Arc2D.Double( 20 , 15 , 280 , 210 ,start,extent,Arc2D.OPEN);
        add(setPanel,BorderLayout.SOUTH);

        pack();
        setResizable( false );
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setVisible( true );

    }
     private   void  setArcByTextField(JTextField textField){
         double  value = 0 ;
         try {
            value =Double.parseDouble(textField.getText().trim());
        } catch (Exception e){
            textField.setText(String.valueOf(textField==startField?start:extent));
             return ;
        }
         if (textField==startField) start =value;
         else                       extent =value;
        arcA =createArc( 20 , 15 , 280 , 210 ,start,extent,Arc2D.OPEN);
        arcB = new  Arc2D.Double( 20 , 15 , 280 , 210 ,start,extent,Arc2D.OPEN);
        repaint();
    }
     public   void  focusGained(FocusEvent e){}
     public   void  focusLost(FocusEvent e){
        setArcByTextField((JTextField)e.getComponent());
    }
     public   void  actionPerformed(ActionEvent e){
        setArcByTextField((JTextField)e.getSource());
    }
     public   static   void  main(String[] args){
         new  ArcT();
    }
}