只使用线和仿射变换来绘制多边形

Question

所以基本上我想做的是只使用仿射变换和一个draw语句来绘制一个任意边数的多边形：g2。绘制（新线条2D（0,0,1,0）。是的，我知道有一个drawPolygon函数——这不是这个问题的重点。为了简单起见，多边形是“正”多边形，这意味着它的所有边和边之间的角度都是相同的。

主要问题是，我不完全理解如何使点正确对齐：

import java.awt.*;
import java.awt.geom.AffineTransform;
import java.awt.geom.Line2D;

import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

public class PolygonDrawer extends JComponent implements Runnable, ChangeListener {

    JFrame jframe;

    public PolygonDrawer() {
        SwingUtilities.invokeLater(this);
    }

    public static void main(String[] args) {
        System.setProperty("awt.useSystemAAFontSettings","on");
        new PolygonDrawer();
    }

    public Dimension getPreferredSize() {
        return new Dimension(200, 200);
    }

    public void run() {
        jframe = new JFrame("PolygonDrawer");
        jframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JPanel mainpanel = new JPanel();
        mainpanel.setLayout(new BorderLayout());
        mainpanel.add(this, BorderLayout.CENTER);
        jframe.getContentPane().add(mainpanel);
        jframe.setVisible(true);
        jframe.pack();
    }

    @Override
    public void stateChanged(ChangeEvent e) {
        repaint();
    }

    @Override
    protected void paintComponent(Graphics g) {
        // Configuration stuff
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D) g;
        Dimension dim = this.getSize();
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        // Fill background
        g2.setColor(Color.white);
        g2.fillRect(0, 0, dim.width, dim.height);

        g2.setColor(Color.black);
        AffineTransform save = g2.getTransform();
        // Example polygon is a regular square
        int noVertices = 4;
        int rotationAngleInDegrees = 90;

        for (int i = 0; i < noVertices; i++) {
            g2.setTransform(save);
            AffineTransform at = new AffineTransform();
            at.rotate(Math.toRadians(i + 1) * rotationAngleInDegrees);
            at.translate(save.getTranslateX(), save.getTranslateY());
            at.scale(100, 1);
            g2.setTransform(at);
            g2.draw(new Line2D.Double(0.0,0.0,1.0,0.0));
            save = g2.getTransform();
        }
    }
}

我想要的只是在屏幕上画一个正方形。然而，台词到处都是。。。我猜这与save的使用方式有关。

Answer 1

它使用仿射变换和一个draw语句。希望有帮助。

    import java.awt.Color;
    import java.awt.Dimension;
    import java.awt.Graphics;
    import java.awt.Graphics2D;
    import java.awt.RenderingHints;
    import java.awt.geom.AffineTransform;
    import java.awt.geom.Line2D;

    import javax.swing.JFrame;
    import javax.swing.JPanel;
    import javax.swing.SwingUtilities;

    public class PolygonDrawer extends JPanel {

       JFrame jframe;
       int    WIDTH  = 500;
       int    HEIGHT = 500;
       int    AX     = 100; 
       int    AY     = 100;

       public static void main(String[] args) {
          SwingUtilities.invokeLater(() -> new PolygonDrawer().start());
       }
       public void start() {
          jframe = new JFrame("PolygonDrawer");
          jframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          setPreferredSize(new Dimension(WIDTH, HEIGHT));
          jframe.add(this);
          jframe.pack();
          jframe.setLocationRelativeTo(null);
          jframe.setVisible(true);
       }

       @Override
       protected void paintComponent(Graphics g) {
          // Configuration stuff
          super.paintComponent(g);
          Graphics2D g2d = (Graphics2D) g.create();
          Dimension dim = this.getSize();
          g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                RenderingHints.VALUE_ANTIALIAS_ON);
          // Fill background
          g2d.setColor(Color.white);
          g2d.fillRect(0, 0, dim.width, dim.height);

          g2d.setColor(Color.black);
          AffineTransform af = g2d.getTransform();

          int noVertices = 6;
          double rotationAngle = ((2 * Math.PI) / noVertices);
          double x1 = WIDTH / 2 - AX;
          double y1 = HEIGHT / 2 - AY;
          af.translate(x1, y1);
          for (int i = 0; i < noVertices; i++) {
             af.rotate(rotationAngle, AX, AY);
             double x2 = af.getTranslateX();
             double y2 = af.getTranslateY();
             g2d.draw(new Line2D.Double(x1, y1, x2, y2));
             x1 = x2;
             y1 = y2;
          }
       }
    }