如何用java2d繪製箭頭？

Question

我想繪製一個箭頭在一個圓圈（如時鐘指針），但我無法對齊箭頭的其餘部分。

我做了「箭頭」根據this answer，但我不能使它正確定位與線條畫。

的箭頭是越到線的左側，在圖像中如下：

這裏我MCVE：

import java.awt.BasicStroke; 
import java.awt.BorderLayout; 
import java.awt.Color; 
import java.awt.Dimension; 
import java.awt.EventQueue; 
import java.awt.Graphics; 
import java.awt.Graphics2D; 
import java.awt.Polygon; 
import java.awt.geom.AffineTransform; 

import javax.swing.JFrame; 
import javax.swing.JPanel; 
import javax.swing.border.EmptyBorder; 

public class LineArrowTest extends JFrame { 

    private static final long serialVersionUID = 1L; 
    private JPanel contentPane; 
    private JPanel DrawPanel; 

    public static void main(String[] args) { 
     EventQueue.invokeLater(() -> { 
      new LineArrowTest().setVisible(true); 
     }); 
    } 

    public LineArrowTest() { 
     initComponents(); 
     pack(); 
    } 

    private void initComponents() { 
     setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     setPreferredSize(new Dimension(400, 300)); 
     this.contentPane = new JPanel(new BorderLayout(0, 0)); 
     this.contentPane.setBorder(new EmptyBorder(5, 5, 5, 5)); 
     setContentPane(this.contentPane); 

     this.DrawPanel = new JPanel() { 

      @Override 
      protected void paintComponent(Graphics g) { 
       super.paintComponent(g); 
       LineArrow line = new LineArrow(getWidth()/2, getHeight()/2, getWidth()/2, getHeight(), 
         Color.black, 3); 
       line.draw(g); 
      } 
     }; 
     this.contentPane.add(this.DrawPanel, BorderLayout.CENTER); 
    } 

    class LineArrow { 

     int x; 
     int y; 
     int endX; 
     int endY; 
     Color color; 
     int thickness; 

     public LineArrow(int x, int y, int x2, int y2, Color color, int thickness) { 
      super(); 
      this.x = x; 
      this.y = y; 
      this.endX = x2; 
      this.endY = y2; 

      this.color = color; 
      this.thickness = thickness; 
     } 

     public void draw(Graphics g) { 
      Graphics2D g2 = (Graphics2D) g.create(); 

      g2.setColor(color); 
      g2.setStroke(new BasicStroke(thickness)); 
      g2.drawLine(x, y, endX, endY); 
      ; 
      drawArrowHead(g2); 
      g2.dispose(); 
     } 

     private void drawArrowHead(Graphics2D g2) { 

      Polygon arrowHead = new Polygon(); 
      AffineTransform tx = new AffineTransform(); 

      arrowHead.addPoint(0, 5); 
      arrowHead.addPoint(-5, -5); 
      arrowHead.addPoint(5, -5); 

      tx.setToIdentity(); 
      double angle = Math.atan2(endY - y, endX - x); 
      tx.translate(endX, endY); 
      tx.rotate(angle - Math.PI/2d); 

      g2.setTransform(tx); 
      g2.fill(arrowHead); 
     } 

    } 

} 

Answer 1

你重新改造。

將AffineTransform tx = new AffineTransform();更改爲AffineTransform tx = g2.getTransform();並刪除tx.setToIdentity();調用。

下面的代碼也被重新排列，以保持相關的語句在一起。

private void drawArrowHead(Graphics2D g2) { 
    double angle = Math.atan2(endY - y, endX - x); 
    AffineTransform tx = g2.getTransform(); 
    tx.translate(endX, endY); 
    tx.rotate(angle - Math.PI/2d); 
    g2.setTransform(tx); 

    Polygon arrowHead = new Polygon(); 
    arrowHead.addPoint(0, 5); 
    arrowHead.addPoint(-5, -5); 
    arrowHead.addPoint(5, -5); 
    g2.fill(arrowHead); 
}