Java Graphics2D浮點準確drawOval的替代？

Question

所以我想繪製一個圓弧並圍繞它的圓形端點放一個圓，但由於四捨五入到最近的像素而產生問題。這在一些情況下可見，但並非全部情況。

有沒有一種方法可以使用浮點和抗鋸齒來消除這個舍入誤差？

您可以運行此代碼來查看問題。爲了清晰起見，我繪製了長度爲0的弧（顯示爲大點）而不是全弧。

import java.awt.*; 
import javax.swing.*; 

public class Example extends JFrame { 

    private int CENTER = 200; 
    private static int WINDOW = 400; 

    private int LEFT = 50; 
    private int TOP = 50; 
    private int DIM = 300; 
    private int DIAMETER = 26; 

    public Example() { 
     super(); 
    } 

    public void paint (Graphics g) { 
     Graphics2D g2 = (Graphics2D) g; 

     g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); 

     g2.setStroke(new BasicStroke(16, BasicStroke.CAP_ROUND, BasicStroke.JOIN_MITER)); 
     g2.setColor(new Color(0, 0, 255)); 

     g2.drawArc(LEFT, TOP, DIM, DIM, 0, 0); 
     g2.drawArc(LEFT, TOP, DIM, DIM, 32, 0); 
     g2.drawArc(LEFT, TOP, DIM, DIM, 115, 0); 
     g2.drawArc(LEFT, TOP, DIM, DIM, 200, 0); 
     g2.drawArc(LEFT, TOP, DIM, DIM, 331, 0); 

     this.drawCircle(g2, 0); 
     this.drawCircle(g2, 32); 
     this.drawCircle(g2, 115); 
     this.drawCircle(g2, 200); 
     this.drawCircle(g2, 331); 

     g2.setStroke(new BasicStroke(1)); 
     g2.setColor(new Color(0, 0, 0)); 
     g2.drawLine(0, CENTER, DIM * 2, CENTER); 
     g2.drawLine(CENTER, 0, CENTER, DIM * 2); 
    } 

    private void drawCircle(Graphics2D g, int angle) { 
     g.setStroke(new BasicStroke(3)); 
     g.setColor(new Color(0, 0, 255)); 
     g.drawOval(
      Math.round(CENTER + (float)(Math.cos(Math.toRadians(angle)) * (DIM/2)) - DIAMETER/2), 
      Math.round(CENTER - (float)(Math.sin(Math.toRadians(angle)) * (DIM/2)) - DIAMETER/2), 
      DIAMETER, 
      DIAMETER 
     ); 
    } 

    public static void main (String args[]) { 
     Example e = new Example(); 
     e.setSize(WINDOW, WINDOW); 
     e.setVisible(true); 
     e.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
    } 
} 

Answer 1

作爲替代方案，可以考慮Ellipse2D與合適RenderingHints。典型用法如here所示。

Ellipse2D circle = new Ellipse2D.Float(…); 
Graphics2D g2d = (Graphics2D) g; 
g2d.setRenderingHints(…); 
g2d.fill(circle); 

因爲各種RenderingHints取決於具體實施，下面的示例將讓您分別評估效果。

import java.awt.BasicStroke; 
import java.awt.Dimension; 
import java.awt.EventQueue; 
import java.awt.Graphics; 
import java.awt.Graphics2D; 
import java.awt.RenderingHints; 
import java.awt.geom.Ellipse2D; 
import javax.swing.JFrame; 
import javax.swing.JPanel; 

/** 
* @see https://stackoverflow.com/a/38669048/230513 
*/ 
public class Test { 

    private void display() { 
     JFrame f = new JFrame("Test"); 
     f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     f.add(new JPanel() { 
      private static final int N = 8; 
      private final Ellipse2D ellipse = new Ellipse2D.Float(); 

      @Override 
      protected void paintComponent(Graphics g) { 
       super.paintComponent(g); 
       Graphics2D g2d = (Graphics2D) g; 
       g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, 
        RenderingHints.VALUE_ANTIALIAS_ON); 
       g2d.setRenderingHint(RenderingHints.KEY_STROKE_CONTROL, 
        RenderingHints.VALUE_STROKE_PURE); 
       g2d.setStroke(new BasicStroke(N)); 
       ellipse.setFrame(N, N, getWidth() - 2 * N, getHeight() - 2 * N); 
       g2d.draw(ellipse); 
      } 

      @Override 
      public Dimension getPreferredSize() { 
       return new Dimension(320, 240); 
      } 
     }); 
     f.pack(); 
     f.setLocationRelativeTo(null); 
     f.setVisible(true); 
    } 

    public static void main(String[] args) { 
     EventQueue.invokeLater(new Test()::display); 
    } 
}