模拟 MSPaint 程序在 java 中绘制以前的笔画而不是仅绘制当前笔画

Question

我的问题： graphics2D 对象重新着色 ArrayList 中的每个点。当我改变颜色时，我将如何做到这一点，它不会改变以前的颜色？我的猜测是改变 for 循环在 PaintApp 中的交互方式，但我不确定我应该做什么。感谢您的帮助！

我的代码：

PaintApp.java

package paint;

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.MouseInfo;
import java.awt.Point;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.util.ArrayList;
import java.util.List;

import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JPanel;

@SuppressWarnings("serial")
public class PaintApp extends JPanel {

    private List<List<Point>> points;
    private JFrame frame = new JFrame("Sketch MSPaint");
    private JMenuBar bar = new JMenuBar();
    private JMenu file = new JMenu("File");
    private JMenu colors = new JMenu("Colors");
    private JMenuItem quit = new JMenuItem("Quit");

    private JMenuItem red = new JMenuItem("Red");
    private JMenuItem blue = new JMenuItem("Blue");
    private JMenuItem green = new JMenuItem("Green");
    private JMenuItem orange = new JMenuItem("Orange");
    private JMenuItem pink = new JMenuItem("Pink");
    private JMenuItem cyan = new JMenuItem("Cyan");

    private JMenuItem clear = new JMenuItem("Clear");
    private boolean clearBoard = false, blackColor, redColor, blueColor, greenColor, orangeColor, pinkColor, cyanColor;

    
    
    public PaintApp(Dimension d) {
        this.setSize(d);
        this.setPreferredSize(d);

        points = new ArrayList<>();
        MouseAdapter ma = new MouseAdapter() {

            private List<Point> currentPath;

            @Override
            public void mousePressed(MouseEvent e) {
                currentPath = new ArrayList<>();
                currentPath.add(e.getPoint());

                points.add(currentPath);
            }

            @Override
            public void mouseDragged(MouseEvent e) {
                Point dragPoint = e.getPoint();
                currentPath.add(dragPoint);
                repaint();
            }

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

        };

        addMouseListener(ma);
        addMouseMotionListener(ma);
    }

    public void paint(Graphics g) {
        super.paint(g);
        Graphics2D g2d = (Graphics2D) g.create();
        g2d.clearRect(0, 0, frame.getWidth(), frame.getHeight());

        for (List<Point> path : points) {
            Point from = null;
            for (Point p : path) {
                if (from != null) {
                    if (redColor) {
                        g2d.setColor(Color.red);
                    } else if (blueColor) {
                        g2d.setColor(Color.blue);
                    } else if (greenColor) {
                        g2d.setColor(Color.green);
                    } else if (orangeColor) {
                        g2d.setColor(Color.orange);
                    } else if (pinkColor) {
                        g2d.setColor(Color.pink);
                    } else if (cyanColor) {
                        g2d.setColor(Color.cyan);
                    } else {
                        g2d.setColor(Color.black);
                    }
                    g2d.drawLine(from.x, from.y, p.x, p.y);
                }
                from = p;
            }
        }
        g2d.dispose();
    }

    public void initBar() {
        bar.add(file);
        file.add(clear);
        clear.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent arg0) {
                points = new ArrayList<>();
                repaint();
            }

        });
        file.add(quit);
        quit.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent arg0) {
                System.exit(0);

            }

        });

        bar.add(colors);
        colors.add(red);
        red.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent arg0) {
                redColor = true;
                blueColor = false;
                greenColor = false;
                orangeColor = false;
                pinkColor = false;
                cyanColor = false;
                repaint();
            }

        });

        colors.add(orange);
        orange.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent arg0) {
                redColor = false;
                blueColor = false;
                greenColor = false;
                orangeColor = true;
                pinkColor = false;
                cyanColor = false;
                repaint();

            }

        });

        colors.add(blue);
        blue.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent arg0) {
                redColor = false;
                blueColor = true;
                greenColor = false;
                orangeColor = false;
                pinkColor = false;
                cyanColor = false;
                repaint();
            }

        });

        colors.add(green);
        quit.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent arg0) {
                redColor = false;
                blueColor = false;
                greenColor = true;
                orangeColor = false;
                pinkColor = false;
                cyanColor = false;
                repaint();

            }

        });

        colors.add(pink);
        quit.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent arg0) {
                redColor = false;
                blueColor = false;
                greenColor = false;
                orangeColor = false;
                pinkColor = true;
                cyanColor = false;
                repaint();

            }

        });

        colors.add(cyan);
        quit.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent arg0) {
                redColor = false;
                blueColor = false;
                greenColor = false;
                orangeColor = false;
                pinkColor = false;
                cyanColor = true;
                repaint();

            }

        });

        frame.setJMenuBar(bar);

    }

    public void show() {
        frame.add(this);
        initBar();
        frame.setResizable(false);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.pack();
        frame.setVisible(true);
    }
}

Main.java

package paint;

import java.awt.Dimension;

public class Main {
    public static void main(String[] args) {
        
        PaintApp app = new PaintApp(new Dimension(700,700));
        
        app.show();
        
    }
}

Answer 1

如果您不想为此提供“撤消”功能，我看到的最简单的解决方案是绘制到 BufferedImage，然后在 paintComponent 覆盖中显示相同的 BufferedImage（不是 paint -- 从不paint）。这样，之前绘制的线条将一直存在，直到您将 BufferedImage 替换为新实例。

否则，如果你绝对不能走这条路，那么创建一个新的自定义类，它包含一个Line2D 或其他 Shape 类型的对象和一个 Color，当用户绘制时创建这些对象，将它们存储到一个 List此类对象，然后在您的 (again) paintComponent 覆盖中使用它们进行绘制。这样，您将每条线（或其他形状）与颜色相关联，并且关联将持续存在。

如上所述，我还建议不要覆盖paint，而是覆盖paintComponent，因为如果您决定制作动画，后者允许自动双缓冲，而且您也不会冒险搞砸绘制组件的子组件和边框，当您覆盖 paint 时，您可能会这样做。当然，在覆盖中调用super.paintComponent(g) 方法，通常在第一行。