java - 单击 2 次鼠标绘制一条线

Question

我试图通过一系列鼠标点击来画一条线。

例如，当我从屏幕上的一个点单击到下一个点时，它会将线条连接起来，然后我可以继续单击到下一个点，它会继续绘制连续的绘图线。

示例如下:http://oneslime.net/java/Tutorial_2在练习2下

我相信我的逻辑有一些错误(没有画线，只是画一个点)，但我似乎找不到它!

有人可以帮我吗？

这是我的代码:

import javax.swing.*;
import java.awt.*;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

public class RoadCreator extends JPanel {

    private MouseHandler mouseHandler = new MouseHandler();

    private Point previousPoint = new Point();
    private Point nextPoint = new Point();
    private boolean drawing;

    public RoadCreator() {
        this.setPreferredSize(new Dimension(640, 480));
        this.addMouseListener(mouseHandler);
       this.addMouseMotionListener(mouseHandler);
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;
        g2d.setColor(Color.blue);
        g2d.setRenderingHint(
            RenderingHints.KEY_ANTIALIASING,
            RenderingHints.VALUE_ANTIALIAS_ON);
        g2d.setStroke(new BasicStroke(8,
            BasicStroke.CAP_ROUND, BasicStroke.JOIN_BEVEL));
        g.drawLine(previousPoint.x, previousPoint.y, nextPoint.x, nextPoint.y);
    }

    private class MouseHandler extends MouseAdapter {

        @Override
        public void mousePressed(MouseEvent e) {
            drawing = true;
            nextPoint = e.getPoint();
            repaint();
            previousPoint = e.getPoint();

        }
    }

    public void display() {
        JFrame f = new JFrame("Road Creator");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(this);
        f.pack();
        f.setVisible(true);
    }

    }

任何帮助将不胜感激，谢谢!

Answer 1

使用 GeneralPath或 Path2D 代替。

The GeneralPath class represents a geometric path constructed from straight lines, and quadratic and cubic (Bézier) curves. It can contain multiple subpaths.

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.GeneralPath;

public class RoadCreator extends JPanel {

    private MouseHandler mouseHandler = new MouseHandler();

    GeneralPath path = null;
    private boolean drawing = false;

    public RoadCreator() {
        this.setPreferredSize(new Dimension(320, 200));
        this.addMouseListener(mouseHandler);
        this.addMouseMotionListener(mouseHandler);
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2d = (Graphics2D) g;
        g2d.setColor(Color.blue);
        g2d.setRenderingHint(
                RenderingHints.KEY_ANTIALIASING,
                RenderingHints.VALUE_ANTIALIAS_ON);
        g2d.setStroke(new BasicStroke(8,
                BasicStroke.CAP_ROUND, BasicStroke.JOIN_BEVEL));
        if (path!=null) {
            g2d.draw(path);
        }
    }

    private class MouseHandler extends MouseAdapter {

        @Override
        public void mousePressed(MouseEvent e) {
            Point p = e.getPoint(); 
            if (!drawing) {
                path = new GeneralPath();
                path.moveTo(p.x, p.y);
                drawing = true;
            } else {
                path.lineTo(p.x, p.y);
            }

            repaint();
        }
    }

    public void display() {
        JFrame f = new JFrame("Road Creator");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(this);
        f.pack();
        f.setVisible(true);
    }

    public static void main(String[] args) {
        RoadCreator rc = new RoadCreator();
        rc.display();
    }
}