关于Arc2D的角度问题

        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();
    }
}