正如评论和当前答案中已经指出的那样，使该drawTree方法与当前绘制的树的哪一部分无关，这一点至关重要。
您不能在此方法中使用绝对坐标。而且您必须跟踪您当前的位置。例如，这可以通过将 a 传递给Point2D描述当前树部分的起点的递归方法来完成。
您甚至不需要显式代码来绘制分支：请注意，单行已经是一棵树。然后树枝只是“较小的树”：它们又是单行，但长度和宽度不同。
（和之前的树相比有一定的角度。你没有提到这个，但角度似乎是Math.PI / 5根据截图）
import java.awt.BasicStroke;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridLayout;
import java.awt.RenderingHints;
import java.awt.geom.Line2D;
import java.awt.geom.Point2D;
import java.util.function.DoubleConsumer;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.SwingUtilities;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;
public class RecursiveTreeDrawing
{
public static void main(String[] args)
{
SwingUtilities.invokeLater(new Runnable()
{
@Override
public void run()
{
createAndShowGUI();
}
});
}
private static void createAndShowGUI()
{
JFrame f = new JFrame();
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.getContentPane().setLayout(new BorderLayout());
RecursiveTreeDrawingPanel p = new RecursiveTreeDrawingPanel();
p.setPreferredSize(new Dimension(500,500));
f.getContentPane().add(p, BorderLayout.CENTER);
JPanel c = new JPanel(new GridLayout(0,1));
c.add(createControl("left length", 0, 0.9,
d -> p.setLeftLengthFactor(d)));
c.add(createControl("left width", 0, 0.9,
d -> p.setLeftWidthFactor(d)));
c.add(createControl("left angle", 0, Math.PI,
d -> p.setLeftAngleDelta(d)));
c.add(createControl("right length", 0, 0.9,
d -> p.setRightLengthFactor(d)));
c.add(createControl("right width", 0, 0.9,
d -> p.setRightWidthFactor(d)));
c.add(createControl("right angle", -Math.PI, 0,
d -> p.setRightAngleDelta(d)));
f.getContentPane().add(c, BorderLayout.SOUTH);
f.pack();
f.setLocationRelativeTo(null);
f.setVisible(true);
}
private static JPanel createControl(
String name, double min, double max, DoubleConsumer doubleConsumer)
{
JPanel p = new JPanel(new GridLayout(1,0));
p.add(new JLabel(name));
JSlider slider = new JSlider(0, 100, 0);
slider.addChangeListener(new ChangeListener()
{
@Override
public void stateChanged(ChangeEvent e)
{
int value = slider.getValue();
double v = value / 100.0;
double d = min + v * (max - min);
doubleConsumer.accept(d);
}
});
p.add(slider);
return p;
}
}
class RecursiveTreeDrawingPanel extends JPanel
{
private double leftLengthFactor = 3.0 / 4.0;
private double leftWidthFactor = 3.0 / 4.0;
private double leftAngleDelta = Math.PI / 5.0;
private double rightLengthFactor = 2.0 / 3.0;
private double rightWidthFactor = 1.0 / 2.0;
private double rightAngleDelta = - Math.PI / 5.0;
@Override
protected void paintComponent(Graphics gr)
{
super.paintComponent(gr);
Graphics2D g = (Graphics2D)gr;
g.setColor(Color.BLACK);
g.fillRect(0,0,getWidth(),getHeight());
g.setRenderingHint(
RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
Point2D start = new Point2D.Double(
getWidth() * 0.5,
getHeight() * 0.7);
g.setColor(Color.GRAY);
drawTree(g, start, 100.0, 2.0, 10.0, 0);
}
private void drawTree(Graphics2D g,
Point2D start, double length, double minLength,
double width, double alpha)
{
if (length < minLength)
{
return;
}
g.setStroke(new BasicStroke((float)width,
BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND));
Point2D end = new Point2D.Double(
start.getX() + Math.sin(alpha + Math.PI) * length,
start.getY() + Math.cos(alpha + Math.PI) * length);
g.draw(new Line2D.Double(start, end));
drawTree(g, end, length * leftLengthFactor, minLength,
width * leftWidthFactor, alpha + leftAngleDelta);
drawTree(g, end, length * rightLengthFactor, minLength,
width * rightWidthFactor, alpha + rightAngleDelta);
}
public void setLeftLengthFactor(double leftLengthFactor)
{
this.leftLengthFactor = leftLengthFactor;
repaint();
}
public void setLeftWidthFactor(double leftWidthFactor)
{
this.leftWidthFactor = leftWidthFactor;
repaint();
}
public void setLeftAngleDelta(double leftAngleDelta)
{
this.leftAngleDelta = leftAngleDelta;
repaint();
}
public void setRightLengthFactor(double rightLengthFactor)
{
this.rightLengthFactor = rightLengthFactor;
repaint();
}
public void setRightWidthFactor(double rightWidthFactor)
{
this.rightWidthFactor = rightWidthFactor;
repaint();
}
public void setRightAngleDelta(double rightAngleDelta)
{
this.rightAngleDelta = rightAngleDelta;
repaint();
}
}
