帮忙用java做一个画图程序的橡皮擦

Question

为一个班级制作一个非常基本的绘画程序，其中一个要求是我们必须制作一个橡皮擦。不知道如何做到这一点，我们正在使用一个缓冲图像，然后将其粘贴到我们的 jframe 中。关于如何做到这一点的任何想法/任何代码示例？有人告诉我尝试clearRect，但也许我只是用错了它，但我无法让它接受它。任何帮助/代码示例都会很棒，这是我的代码，都是一类。

     import javax.imageio.ImageIO;
     import javax.swing.*;
     import javax.swing.border.Border;
     import javax.swing.border.LineBorder;

     import java.awt.*;
     import java.awt.event.*;
     import java.awt.image.BufferedImage;
     import java.io.File;
     import java.io.IOException;
     import java.util.*;


     public class PaintProgram extends JPanel implements MouseListener,ActionListener
     {
public static int stroke, eraser = 0;
private int xX1, yY1 , xX2, yY2, choice ;

public static void main(String [] args)
{
    new PaintProgram();
}

PaintProgram()
{


    JFrame frame = new JFrame("Paint Program");
    frame.setSize(1200, 800);
    frame.setBackground(Color.WHITE);
    frame.getContentPane().add(this);


    JMenuBar menuBar = new JMenuBar();
    frame.setJMenuBar(menuBar);
    JMenu help = new JMenu("Help");
    menuBar.add(help);
    JMenuItem about = new JMenuItem("About");
    help.add(about);
    about.addActionListener(this);



    JButton button1 = new JButton("Clear");
    button1.addActionListener(this);
    JButton color = new JButton("Color");
    color.addActionListener(this);
    JButton erase = new JButton("Erase?");
    erase.addActionListener(this);
    JButton button2 = new JButton("Empty Rect");
    button2.addActionListener(this);
    JButton button3 = new JButton("Filled oval");
    button3.addActionListener(this);
    JButton button4 = new JButton("Filled Rect");
    button4.addActionListener(this);
    JButton button5 = new JButton("Empty oval");
    button5.addActionListener(this);
    JButton button6 = new JButton("Line");
    button6.addActionListener(this);
    JRadioButton thin = new JRadioButton("Thin Line");
    thin.addActionListener(this);
    JRadioButton medium = new JRadioButton("Medium Line");
    medium.addActionListener(this);
    JRadioButton thick = new JRadioButton("Thick Line");
    thick.addActionListener(this);


    ButtonGroup lineOption = new ButtonGroup( );
    lineOption.add(thin);
    lineOption.add(medium);
    lineOption.add(thick);

   this.add(button1); 
   this.add(color);
   this.add(erase);
   this.add(button2);
   this.add(button3);
   this.add(button4);
   this.add(button5);
   this.add(button6);
   this.add(thin);
   this.add(medium);
   this.add(thick);
   addMouseListener(this);
   frame.setVisible(true);
   frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);



}

public void paintComponent(Graphics g)
{ 
     super.paintComponent(g);  
     Graphics2D g2 = (Graphics2D)g;
     if(grid == null){
        int w = this.getWidth();
        int h = this.getHeight();
        grid = (BufferedImage)(this.createImage(w,h));
        gc = grid.createGraphics();
        gc.setColor(Color.BLUE);
     }

     g2.drawImage(grid, null, 0, 0);
     check();
}
BufferedImage grid;
Graphics2D gc;


public void draw()
{
    Graphics2D g = (Graphics2D)getGraphics();
     int w = xX2 - xX1;
        if (w<0)
        w = w *(-1);

   int h = yY2-yY1;
        if (h<0)
        h=  h*(-1);

     switch(choice)
    {
        case 1:
            check();
            gc.drawRect(xX1, yY1, w, h);
            repaint();
            break;

        case 2:
            check();
            gc.drawOval(xX1, yY1, w, h);
            repaint();
            break;

        case 3:
            check();
            gc.drawRect(xX1, yY1, w, h);
            gc.fillRect(xX1, yY1, w, h);
            repaint();
            break;

        case 4:
            check();
            gc.drawOval(xX1, yY1, w, h);
            gc.fillOval(xX1, yY1, w, h);
            repaint();
            break;  

        case 5:

            if (stroke == 0)
            gc.setStroke(new BasicStroke (1));
            if (stroke == 1)
            gc.setStroke(new BasicStroke (3));
            if (stroke == 2)
            gc.setStroke(new BasicStroke (6));
            gc.drawLine(xX1, yY1, xX2, yY2);
            repaint();
            break;

        case 6:
            repaint();
            Color temp = gc.getColor();
            gc.setColor(Color.WHITE);
            gc.fillRect(0, 0, getWidth(), getHeight());
            gc.setColor(temp);
            repaint();
            break;   

        case 7:

            if (eraser == 1)
            {
                gc.clearRect(xX1, yY1, w, h);
            }
            else
            {

            }
            break;
    }
}

public void check()
{
    if (xX1 > xX2)
    {
        int z = 0;
        z = xX1;
        xX1 = xX2;
        xX2 =z;
    }
    if (yY1 > yY2)
    {
        int z = 0;
        z = yY1;
        yY1 = yY2;
        yY2 = z;
    }
}




public void actionPerformed(ActionEvent e)
{

if (e.getActionCommand().equals("Color"))
{
     Color bgColor
     = JColorChooser.showDialog(this,"Choose Background Color", getBackground());
   if (bgColor != null)
     gc.setColor(bgColor);
}


if (e.getActionCommand().equals("About"))
{
    System.out.println("About Has Been Pressed");
    JFrame about = new JFrame("About");
    about.setSize(300, 300);
    JButton picture = new JButton(new ImageIcon("C:/Users/TehRobot/Desktop/Logo.png"));
    about.add(picture);
    about.setVisible(true);
}

if (e.getActionCommand().equals("Empty Rect")) 
{         
  System.out.println("Empty Rectangle Has Been Selected~");
   choice = 1;

  }

if (e.getActionCommand().equals("Empty oval")) 
{         
 System.out.println("Empty Oval Has Been Selected!");
   choice = 2;
  }


if (e.getActionCommand().equals("Filled Rect"))
{         
  System.out.println("Filled Rectangle Has Been Selected");
   choice = 3;
  }


if (e.getActionCommand().equals("Filled oval")) 
{         
 System.out.println("Filled Oval Has Been Selected");
   choice = 4;
  }


if (e.getActionCommand().equals("Line"))
{
    System.out.println("Draw Line Has Been Selected");
    choice = 5;
}

if (e.getActionCommand().equals("Thin Line"))
{
    stroke = 0;
}

if (e.getActionCommand().equals("Medium Line"))
{
    stroke = 1;
}

if (e.getActionCommand().equals("Thick Line"))
{
    stroke = 2;
}

if(e.getActionCommand().equals("Erase?"))
{
    eraser = 1;
    choice = 7;
}

if (e.getActionCommand().equals("Clear"))
{         
    System.out.println("Clear All The Things!!!");
    choice = 6;
    draw();
}


 }

 public void mouseExited(MouseEvent evt){}
 public void mouseEntered(MouseEvent evt){}
 public void mouseClicked(MouseEvent evt){}
 public void mousePressed(MouseEvent evt)
 {

     xX1 = evt.getX();
     yY1= evt.getY();



   }
 public void mouseReleased(MouseEvent evt)
 {
     xX2 =evt.getX();
     yY2=evt.getY();
     draw();
     eraser = 0;
   }

}

Answer 1

我在添加/更改代码的地方添加了注释。

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.awt.image.BufferedImage;

import javax.swing.ButtonGroup;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JColorChooser;
import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JPanel;
import javax.swing.JRadioButton;

public class PaintProgram extends JPanel implements MouseListener, ActionListener,
/**
 * CHANGE BY S AQEEL : implement mouse motion listener
 */
MouseMotionListener
{
    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    public static int stroke, eraser = 0;
    private int xX1, yY1, xX2, yY2, choice;

    /**
     * CHANGE BY S AQEEL : Define a constant for background color, because we are using it at a lot of places
     */
    private static final Color BACKGROUND_COLOR = Color.WHITE;

    /**
     * CHANGE BY S AQEEL : Also define variables for eraser width and height. In a more usable implementation you can allow user to change eraser size
     */
    private int eraserWidth = 40;
    private int eraserHeight = 40;

    public static void main(String[] args)
    {
        new PaintProgram();
    }

    PaintProgram()
    {

        JFrame frame = new JFrame("Paint Program");
        frame.setSize(1200, 800);

        /**
         * CHANGE BY S AQEEL : Use constant instead of hardcoding
         */
        frame.setBackground(BACKGROUND_COLOR);
        frame.getContentPane().add(this);

        JMenuBar menuBar = new JMenuBar();
        frame.setJMenuBar(menuBar);
        JMenu help = new JMenu("Help");
        menuBar.add(help);
        JMenuItem about = new JMenuItem("About");
        help.add(about);
        about.addActionListener(this);

        JButton button1 = new JButton("Clear");
        button1.addActionListener(this);
        JButton color = new JButton("Color");
        color.addActionListener(this);
        JButton erase = new JButton("Erase?");
        erase.addActionListener(this);
        JButton button2 = new JButton("Empty Rect");
        button2.addActionListener(this);
        JButton button3 = new JButton("Filled oval");
        button3.addActionListener(this);
        JButton button4 = new JButton("Filled Rect");
        button4.addActionListener(this);
        JButton button5 = new JButton("Empty oval");
        button5.addActionListener(this);
        JButton button6 = new JButton("Line");
        button6.addActionListener(this);
        JRadioButton thin = new JRadioButton("Thin Line");
        thin.addActionListener(this);
        JRadioButton medium = new JRadioButton("Medium Line");
        medium.addActionListener(this);
        JRadioButton thick = new JRadioButton("Thick Line");
        thick.addActionListener(this);

        ButtonGroup lineOption = new ButtonGroup();
        lineOption.add(thin);
        lineOption.add(medium);
        lineOption.add(thick);

        this.add(button1);
        this.add(color);
        this.add(erase);
        this.add(button2);
        this.add(button3);
        this.add(button4);
        this.add(button5);
        this.add(button6);
        this.add(thin);
        this.add(medium);
        this.add(thick);
        addMouseListener(this);
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    }

    public void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D) g;
        if (grid == null)
        {
            int w = this.getWidth();
            int h = this.getHeight();
            grid = (BufferedImage) (this.createImage(w, h));
            gc = grid.createGraphics();
            gc.setColor(Color.BLUE);
        }

        g2.drawImage(grid, null, 0, 0);
        check();
    }

    BufferedImage grid;
    Graphics2D gc;

    public void draw()
    {
        Graphics2D g = (Graphics2D) getGraphics();
        int w = xX2 - xX1;
        if (w < 0)
            w = w * (-1);

        int h = yY2 - yY1;
        if (h < 0)
            h = h * (-1);

        switch (choice)
        {
        case 1:
            check();
            gc.drawRect(xX1, yY1, w, h);
            repaint();
            break;

        case 2:
            check();
            gc.drawOval(xX1, yY1, w, h);
            repaint();
            break;

        case 3:
            check();
            gc.drawRect(xX1, yY1, w, h);
            gc.fillRect(xX1, yY1, w, h);
            repaint();
            break;

        case 4:
            check();
            gc.drawOval(xX1, yY1, w, h);
            gc.fillOval(xX1, yY1, w, h);
            repaint();
            break;

        case 5:

            if (stroke == 0)
                gc.setStroke(new BasicStroke(1));
            if (stroke == 1)
                gc.setStroke(new BasicStroke(3));
            if (stroke == 2)
                gc.setStroke(new BasicStroke(6));
            gc.drawLine(xX1, yY1, xX2, yY2);
            repaint();
            break;

        case 6:
            repaint();
            Color temp = gc.getColor();

            /**
             * CHANGE BY S AQEEL : Use constant instead of hardcoding
             */
            gc.setColor(BACKGROUND_COLOR);
            gc.fillRect(0, 0, getWidth(), getHeight());
            gc.setColor(temp);
            repaint();
            break;

        case 7:

            if (eraser == 1)
            {
                gc.clearRect(xX1, yY1, w, h);
            }
            else
            {

            }
            break;
        }
    }

    public void check()
    {
        if (xX1 > xX2)
        {
            int z = 0;
            z = xX1;
            xX1 = xX2;
            xX2 = z;
        }
        if (yY1 > yY2)
        {
            int z = 0;
            z = yY1;
            yY1 = yY2;
            yY2 = z;
        }
    }

    public void actionPerformed(ActionEvent e)
    {
        /**
         * CHANGE BY S AQEEL : Remove mousemotionlistener(which is added when eraser is selected) So that if another control is pressed, the user does
         * not accidentally erases
         */
        super.removeMouseMotionListener(this);

        if (e.getActionCommand().equals("Color"))
        {
            Color bgColor = JColorChooser.showDialog(this, "Choose Background Color", getBackground());
            if (bgColor != null)
                gc.setColor(bgColor);
        }

        if (e.getActionCommand().equals("About"))
        {
            System.out.println("About Has Been Pressed");
            JFrame about = new JFrame("About");
            about.setSize(300, 300);
            JButton picture = new JButton(new ImageIcon("C:/Users/TehRobot/Desktop/Logo.png"));
            about.add(picture);
            about.setVisible(true);
        }

        if (e.getActionCommand().equals("Empty Rect"))
        {
            System.out.println("Empty Rectangle Has Been Selected~");
            choice = 1;

        }

        if (e.getActionCommand().equals("Empty oval"))
        {
            System.out.println("Empty Oval Has Been Selected!");
            choice = 2;
        }

        if (e.getActionCommand().equals("Filled Rect"))
        {
            System.out.println("Filled Rectangle Has Been Selected");
            choice = 3;
        }

        if (e.getActionCommand().equals("Filled oval"))
        {
            System.out.println("Filled Oval Has Been Selected");
            choice = 4;
        }

        if (e.getActionCommand().equals("Line"))
        {
            System.out.println("Draw Line Has Been Selected");
            choice = 5;
        }

        if (e.getActionCommand().equals("Thin Line"))
        {
            stroke = 0;
        }

        if (e.getActionCommand().equals("Medium Line"))
        {
            stroke = 1;
        }

        if (e.getActionCommand().equals("Thick Line"))
        {
            stroke = 2;
        }

        if (e.getActionCommand().equals("Erase?"))
        {
            eraser = 1;
            choice = 7;

            /**
             * CHANGE BY S AQEEL : Add mousemotionlistener here.
             */
            super.addMouseMotionListener(this);
        }

        if (e.getActionCommand().equals("Clear"))
        {
            System.out.println("Clear All The Things!!!");
            choice = 6;
            draw();
        }

    }

    public void mouseExited(MouseEvent evt)
    {
    }

    public void mouseEntered(MouseEvent evt)
    {
    }

    public void mouseClicked(MouseEvent evt)
    {
    }

    public void mousePressed(MouseEvent evt)
    {

        xX1 = evt.getX();
        yY1 = evt.getY();

    }

    public void mouseReleased(MouseEvent evt)
    {
        xX2 = evt.getX();
        yY2 = evt.getY();
        draw();
        eraser = 0;
    }

    /**
     * CHANGE BY S AQEEL : MouseMotionListener functions implemented. Note this listener is only registered when eraser is selected
     */
    public void mouseDragged(MouseEvent me)
    {
        Color c = gc.getColor();
        gc.setColor(BACKGROUND_COLOR);
        gc.drawRect(me.getX(), me.getY(), eraserWidth, eraserHeight);
        gc.fillRect(me.getX(), me.getY(), eraserWidth, eraserHeight);
        gc.setColor(c);
        repaint();
    }

    public void mouseMoved(MouseEvent arg0)
    {
    }
}

既然您的问题已经解决，您应该尝试添加一些少量但可用的质量功能，例如：使用不同的光标来绘制/擦除不同的形状。允许用户更改橡皮擦尺寸。另外，在当前的实现中，用户必须拖动橡皮擦才能擦除，您应该添加一个功能，以便用户只需单击（除了拖动之外）即可擦除点。

Answer 2

橡皮擦就像笔一样，只不过它将颜色设置为背景颜色。当您擦除时，您会将笔下的当前颜色替换为“背景”颜色，这使其看起来像背景，从而有效地消除了先前在屏幕上绘制的感知颜色。

如果您的应用程序处理透明度，那么您的橡皮擦可能会将颜色设置为透明；但这是相同的想法，因为“透明度”只是颜色成分之一，如红色、绿色和蓝色。

如果您想要一个按钮来擦除整个绘图，则只需以背景色绘制一个与屏幕一样大的矩形即可。