如何修复此绘图程序，以便在选择另一个像素时，从一条线绘制的最后一个像素不会变为不同的颜色？

Posted 2023-03-27

【中文标题】如何修复此绘图程序，以便在选择另一个像素时，从一条线绘制的最后一个像素不会变为不同的颜色？

【英文标题】：How can I fix this paint program so that the last pixel drawn from a line does not change to a different color when another is selected?

【发布时间】：2016-09-23 15:42:27

【问题描述】：

    import java.awt.*;
    import java.applet.*;


    public class lab13 extends Applet 
    

    Rectangle pencil;
    Rectangle red;
    Rectangle blue;
    Rectangle green;
    Rectangle purple;
    Rectangle drawArea;


    Image virtualMem;
    Graphics gBuffer;

    int newX; 
    int newY;


    int appletWidth;
    int appletHeight;

    int drawnPoint;
    int choice;

    public void init()
    
        appletWidth = getWidth();
        appletHeight = getHeight();
        virtualMem = createImage(appletWidth,appletHeight);
        gBuffer = virtualMem.getGraphics();
        gBuffer.setColor(Color.WHITE);
        gBuffer.fillRect(0,0,appletWidth,appletHeight);

        pencil = new Rectangle(10,10,50,50);
        red = new Rectangle(10,70,50,50);
        blue = new Rectangle(10,130,50,50);
        green = new Rectangle(10,190,50,50);
        purple = new Rectangle(10,250,50,50);

        drawArea = new Rectangle(85,10,290,380);

        gBuffer.drawRect(85,10,290,380);

        gBuffer.setColor(Color.BLACK);
        gBuffer.fillRect(10,10,50,50);

        gBuffer.setColor(Color.RED);
        gBuffer.fillRect(10,70,50,50);

        gBuffer.setColor(Color.BLUE);
        gBuffer.fillRect(10,130,50,50);

        gBuffer.setColor(Color.GREEN);
        gBuffer.fillRect(10,190,50,50);

        gBuffer.setColor(new Color(218,112,214));
        gBuffer.fillRect(10,250,50,50);

        choice = 0;
    

    public void paint(Graphics g)
    

        gBuffer.setColor(Color.WHITE);          //This is a quick fix for a colored pixel in the top left hand corner
        gBuffer.fillRect(0,0,3,3);


        switch(choice)
        
            case 1:
                gBuffer.setColor(Color.BLACK);
                break;
            case 2:
                gBuffer.setColor(Color.red);
                break;
            case 3:
                gBuffer.setColor(Color.BLUE);
                break;
            case 4:
                gBuffer.setColor(Color.GREEN);
                break;
            case 5:
                gBuffer.setColor(new Color(218,112,214));
                break;
        

            gBuffer.fillRect(newX,newY,3,3);
            g.drawImage(virtualMem,0,0,this);

    





    public boolean mouseDown(Event e, int x, int y)
    
        if (pencil.inside(x,y))
            choice = 1;
        else if (red.inside(x,y))
            choice = 2;
        else if (blue.inside(x,y))
            choice = 3;
        else if (green.inside(x,y))
            choice = 4;
        else if (purple.inside(x,y))
            choice = 5;
        repaint();
        return true;

    

    public boolean mouseDrag(Event e, int x, int y)
    
        if(drawArea.inside(x,y))
        
            newX = x;
            newY = y;
            repaint();
        
        return true;

    




    public void update(Graphics g)
     
        paint(g);
     

这是我们正在为学校的实验室做的一个绘画程序。我遇到的问题是，在我画一条线并选择不同的颜色后，前一条线的最后一部分将颜色更改为被选中的颜色，而不是保持统一的颜色。我真的不知道在哪里寻找问题。我试过改变。我怀疑它可能是我的绘画方法结束时的 drawImage 。这将是我发布后尝试和玩的东西。任何帮助将不胜感激！

【问题讨论】：

Java Plugin support deprecated 和 Moving to a Plugin-Free Web

创建一个自定义类，它可能从 Rectangle 扩展而来，它还带有应该绘制的颜色

【参考方案1】：

您需要设置一些标志来确定颜色发生了变化，而不是用新颜色重绘矩形。有很多不同的方法可以实现这一点，这里有一个：

如果颜色发生变化，请将newX 和newY 设置为某个无效值：

@Override
public boolean mouseDown(final Event e, final int x, final int y) 
    int choiceNew = 0;

    if (pencil.inside(x, y)) 
        choiceNew = 1;
     else if (red.inside(x, y)) 
        choiceNew = 2;
     else if (blue.inside(x, y)) 
        choiceNew = 3;
     else if (green.inside(x, y)) 
        choiceNew = 4;
     else if (purple.inside(x, y)) 
        choiceNew = 5;
    

    if ((choiceNew > 0) && (choice != choiceNew)) 
        choice = choiceNew;
        newX = -1;
        newY = -1;
     else 
        newX = x;
        newY = y;
    

    repaint();
    return true;

然后在绘画时，检查那个标志：

@Override
public void paint(final Graphics g) 
    gBuffer.setColor(Color.WHITE); //This is a quick fix for a colored pixel in the top left hand corner
    gBuffer.fillRect(0, 0, 3, 3);

    switch (choice) 
        case 1:
            gBuffer.setColor(Color.BLACK);
            break;
        case 2:
            gBuffer.setColor(Color.red);
            break;
        case 3:
            gBuffer.setColor(Color.BLUE);
            break;
        case 4:
            gBuffer.setColor(Color.GREEN);
            break;
        case 5:
            gBuffer.setColor(new Color(218, 112, 214));
            break;
    

    if ((newX != -1) && (newY != -1)) 
        gBuffer.fillRect(newX, newY, 3, 3);
    

    g.drawImage(virtualMem, 0, 0, this);