我应该如何绘制一个三角形？

Question

我知道如何使用g.drawRect或者g.drawOval绘制矩形和圆等图形。但是没有g.drawtriangle，有没有一种方法可以在不必手动绘制每个三角形边的情况下绘制三角形呢？

- jack zhang

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请点击以下链接查看有关绘制三角形的方法：https://dev59.com/_Wct5IYBdhLWcg3wqfH9 - Oleks

Answer 1

您可以使用Graphics.drawPolygon(int[], int[], int)方法，其中第一个int[]是x值集合，第二个int[]是y值集合，int表示数组的长度。(对于三角形，int将为3)

示例：

graphics.drawPolygon(new int[] {10, 20, 30}, new int[] {100, 20, 100}, 3);

输出：

- Constant

Answer 2

我会使用Path2D对象，并通过其moveTo(...)方法放置第一个点，然后使用其lineTo(...)方法添加其他点。接下来，您可以通过Graphics2D#draw(...)和Graphics2D#fill(...)方法来绘制或填充该三角形。同时，在其上调用closePath()方法将确保您的三角形正确关闭。

例如，以下代码产生：

import java.awt.Color;
import java.awt.Dimension;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Paint;
import java.awt.RenderingHints;
import java.awt.geom.Path2D;    
import javax.swing.*;

public class Path2DExample extends JPanel {
   private static final int PREF_W = 600;
   private static final int PREF_H = PREF_W;
   private static final Color COLOR_1 = Color.blue;
   private static final Color COLOR_2 = Color.red;
   private static final Paint GRADIENT_PAINT = new GradientPaint(0, 0, COLOR_1, 20, 20, COLOR_2, true);
   private Path2D myPath = new Path2D.Double();

   public Path2DExample() {
      double firstX = (PREF_W / 2.0) * (1 - 1 / Math.sqrt(3));
      double firstY = 3.0 * PREF_H / 4.0;

      myPath.moveTo(firstX, firstY);
      myPath.lineTo(PREF_W - firstX, firstY);
      myPath.lineTo(PREF_W / 2.0, PREF_H / 4.0);
      myPath.closePath();
   }

   @Override
   protected void paintComponent(Graphics g) {
      super.paintComponent(g);
      Graphics2D g2 = (Graphics2D) g;

      // to smooth out the jaggies
      g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
            RenderingHints.VALUE_ANTIALIAS_ON);
      g2.setPaint(GRADIENT_PAINT);  // just for fun!
      g2.fill(myPath);  // fill my triangle
   }

   @Override
   public Dimension getPreferredSize() {
      if (isPreferredSizeSet()) {
         return super.getPreferredSize();
      }
      return new Dimension(PREF_W, PREF_H);
   }

   private static void createAndShowGui() {
      Path2DExample mainPanel = new Path2DExample();

      JFrame frame = new JFrame("Path2DExample");
      frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}

使用Path2D对象的另一个好处是，如果你想拖动该形状，使用MouseListener和MouseMotionListener并不难，可以这样做：

---

使用Path2D对象的另一个好处是，如果您想要拖动该形状，则使用MouseListener和MouseMotionListener非常容易，例如：

private class MyMouseAdapter extends MouseAdapter {
  private Point pPressed = null;

  @Override
  public void mousePressed(MouseEvent e) {
     if (e.getButton() != MouseEvent.BUTTON1) {
        return;
     }
     if (myPath.contains(e.getPoint())) {
        pPressed = e.getPoint();
     }
  }

  public void mouseDragged(MouseEvent e) {
     drag(e);
  }

  @Override
  public void mouseReleased(MouseEvent e) {
     drag(e);
     pPressed = null;
  }

  private void drag(MouseEvent e) {
     if (pPressed == null) {
        return;
     }
     Point p = e.getPoint();
     int tx = p.x - pPressed.x;
     int ty = p.y - pPressed.y;
     AffineTransform at = AffineTransform.getTranslateInstance(tx, ty);
     myPath.transform(at);
     pPressed = p;
     repaint();
  };

}

整个事情可能看起来像这样：

import java.awt.Color;
import java.awt.Dimension;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Paint;
import java.awt.Point;
import java.awt.RenderingHints;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.AffineTransform;
import java.awt.geom.Path2D;
import javax.swing.*;

@SuppressWarnings("serial")
public class Path2DExample extends JPanel {
   private static final int PREF_W = 600;
   private static final int PREF_H = PREF_W;
   private static final Color COLOR_1 = Color.blue;
   private static final Color COLOR_2 = Color.red;
   private static final Paint GRADIENT_PAINT = new GradientPaint(0, 0, COLOR_1,
         20, 20, COLOR_2, true);
   private Path2D myPath = new Path2D.Double();

   public Path2DExample() {
      double firstX = (PREF_W / 2.0) * (1 - 1 / Math.sqrt(3));
      double firstY = 3.0 * PREF_H / 4.0;

      myPath.moveTo(firstX, firstY);
      myPath.lineTo(PREF_W - firstX, firstY);
      myPath.lineTo(PREF_W / 2.0, PREF_H / 4.0);
      myPath.closePath();

      MyMouseAdapter myMouseAdapter = new MyMouseAdapter();
      addMouseListener(myMouseAdapter);
      addMouseMotionListener(myMouseAdapter);
   }

   @Override
   protected void paintComponent(Graphics g) {
      super.paintComponent(g);
      Graphics2D g2 = (Graphics2D) g;
      g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
            RenderingHints.VALUE_ANTIALIAS_ON);
      g2.setPaint(GRADIENT_PAINT);
      g2.fill(myPath);
   }

   @Override
   public Dimension getPreferredSize() {
      if (isPreferredSizeSet()) {
         return super.getPreferredSize();
      }
      return new Dimension(PREF_W, PREF_H);
   }

   private class MyMouseAdapter extends MouseAdapter {
      private Point pPressed = null;

      @Override
      public void mousePressed(MouseEvent e) {
         if (e.getButton() != MouseEvent.BUTTON1) {
            return;
         }
         if (myPath.contains(e.getPoint())) {
            pPressed = e.getPoint();
         }
      }

      public void mouseDragged(MouseEvent e) {
         drag(e);
      }

      @Override
      public void mouseReleased(MouseEvent e) {
         drag(e);
         pPressed = null;
      }

      private void drag(MouseEvent e) {
         if (pPressed == null) {
            return;
         }
         Point p = e.getPoint();
         int tx = p.x - pPressed.x;
         int ty = p.y - pPressed.y;
         AffineTransform at = AffineTransform.getTranslateInstance(tx, ty);
         myPath.transform(at);
         pPressed = p;
         repaint();
      };

   }

   private static void createAndShowGui() {
      Path2DExample mainPanel = new Path2DExample();

      JFrame frame = new JFrame("Path2DExample");
      frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}

- Hovercraft Full Of Eels