java - 更改 JPanel Graphics g 颜色绘图线

Question

我有一个类似于画图的程序。并且我正在尝试实现更改笔颜色但是当我更改颜色时，当前绘制的所有内容都更改为红色，例如在我的程序中，我怎样才能做到它不会重新绘制当前绘制的所有内容到当前颜色变了？下面的代码会编译运行

JPanel 绘图区的类

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.Rectangle;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.ArrayList;
import javax.swing.BorderFactory;
import javax.swing.JPanel;
//refer to http://jkost.ergoway.gr/jnkjavaconnection/freedraw.html for the algorithm.
public class STDrawingArea extends JPanel {
    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    ArrayList<Rectangle> dPoint = new ArrayList<Rectangle>();
    Point point = new Point(-1,-1);
    private Color currentColor;

    public STDrawingArea()
    {
         setBorder(BorderFactory.createLineBorder(Color.black));
         setBackground(Color.WHITE);

         addMouseMotionListener(new MouseAdapter() {
            public void mouseDragged(MouseEvent e) 
            {
                dPoint.add(new Rectangle(point.x,point.y,e.getX(),e.getY()));
                point.x = e.getX();
                point.y = e.getY();
                repaint();
            }

             });

         addMouseListener(new MouseAdapter(){
             public void mousePressed(MouseEvent e)
             {
                 System.out.println("mousePressed X: "+e.getX()+"mousePressed Y: "+e.getY());
                 dPoint.add(new Rectangle(e.getX(),e.getY(),-1,-1));
                 point.x = e.getX();
                 point.y = e.getY();
             }
         });

         addMouseListener(new MouseAdapter(){
             public void mouseReleased(MouseEvent e)
             {
                 System.out.println("mouseReleased X: "+e.getX()+"mouseReleased Y: "+e.getY());
                 repaint();
             }
         });
    }

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(700,500);
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
       g.setColor(getCurrentColor());
        for (int i=0; i < dPoint.size(); i++) {  
            Rectangle r = dPoint.get(i);
            if (r.width != -1)
            {
              g.drawLine(r.x, r.y, r.width, r.height);  
            }
           }  
            /* Draw current point.*/ 
            g.drawLine(point.x, point.y, point.x, point.y);  
    }

    //set current drawing color
    public void changePenColor(Color color)
    {
        if (color == null)
        setCurrentColor(Color.BLACK);
        else
        setCurrentColor(color);
    }

    //clear drawings method
    public void clearDrawings()
    {
        if(!(dPoint==null))
        {
             dPoint.clear();
             repaint();
        }

    }

    private void setCurrentColor(Color currentColor) {
        this.currentColor = currentColor;
    }

    private Color getCurrentColor() {
        return currentColor;
    }
}

测试主类。

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;


public class STTestMain extends JFrame {
    STDrawingArea drawingArea = new STDrawingArea();
    public STTestMain()
    {
        //JFrame settings
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setTitle("Spelling Trainer");
        setResizable(false);
        setVisible(true);


        //Panel of buttons
        JPanel buttonContainer = new JPanel();
        JButton btnPenColor = new JButton("Red Pen");

        buttonContainer.add(btnPenColor);
        //Drawing Area instantiation


        //Adding things to JFrame
        getContentPane().add(drawingArea);
        getContentPane().add(buttonContainer,BorderLayout.PAGE_END);
        pack();


        //button listener
        btnPenColor.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                // TODO Auto-generated method stub
                drawingArea.changePenColor(Color.RED);
            }
        });
    }


    public static void main(String args[])
    {
        STTestMain test = new STTestMain();
    }

}

Answer 1

一种方式:

• 使用 ArrayList 绘制当前曲线，但是
• 使用 BufferedImage 绘制完成的曲线
• 您可以在 mouseReleased 上执行此操作，并使用当前颜色将当前曲线绘制到 BufferedImage。
• 在绘制到 BufferedImage 之后，您还需要重新初始化点的 ArrayList。
• 不要忘记在使用完 BufferedImage 的 Graphics 对象后释放它。
• 在 super.paintComponent 之后但在绘制当前曲线之前，在 paintComponent 方法中绘制 BufferedImage。
• 这样，当您更改绘图的颜色时，只会影响当前曲线。

编辑
您在评论中提到您不熟悉 BufferedImage，正在寻找另一种方式。我想您可以创建一个类，其中包含点的 ArrayList 和颜色，然后在每个 mouseReleased 上创建此类的对象并将其添加到绘图面板中的 ArrayList。然后，您的 paintComponent 方法可以遍历该 ArrayList，绘制具有相关颜色的 Points 列表，但我的直觉告诉我您是一个聪明人，您很快就会学会如何使用 BufferedImage。我真的认为这是最好的解决方案。如果您尝试它但失败了，请向我们展示您的代码，我们很可能会帮助您。

编辑 2
BufferedImage 构造函数需要图像宽度、高度和图像类型——我不是 100% 熟悉的。我通常将 BufferedImage.TYPE_INT_RGB 用于通用绘图，将 BufferedImage.TYPE_INT_ARGB 用于也需要 alpha 的通用用途。然后你将从 BufferedImage 中提取一个 Graphics 对象，如果你需要的只是一个 Graphics 对象而不是 Graphics2D 对象，就说 getGraphics() 。然后，当您在构造函数中初始化 BufferedImage 时，用 Color.white 填充它，就像您对 JPanel 一样。然后处置 Graphics 对象。然后每次你想画的时候，你getGraphics，用它画，就像你在paintComponent方法中做的那样，完成后处理Graphics，最后通过drawImage方法在paintComponent中绘制BufferedImage。

编辑 3
示例程序不完全符合您的要求，但确实说明了使用 BufferedImage 进行绘图。每次绘制新路径或曲线时，该程序都会更改颜色。

import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import java.util.ArrayList;
import javax.swing.*;

public class STTestSimple {
   private static void createAndShowUI() {
      STDrawPanel drawPanel = new STDrawPanel();
      STMouseAdapter mAdapter = new STMouseAdapter(drawPanel);
      drawPanel.addMouseListener(mAdapter);
      drawPanel.addMouseMotionListener(mAdapter);

      JFrame frame = new JFrame("Drawing");
      frame.getContentPane().add(drawPanel);
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.setResizable(false);
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      java.awt.EventQueue.invokeLater(new Runnable() {
         public void run() {
            createAndShowUI();
         }
      });
   }
}

@SuppressWarnings("serial")
class STDrawPanel extends JPanel {
   private static final int ST_WIDTH = 700;
   private static final int ST_HEIGHT = 500;
   private static final Color BACKGROUND_COLOR = Color.white;
   private static final float STROKE_WIDTH = 6f;
   private static final Stroke STROKE = new BasicStroke(STROKE_WIDTH,
            BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND);
   private static final Color[] colors = {Color.black, Color.blue, Color.red,
      Color.green, Color.orange, Color.MAGENTA};

   private BufferedImage bImage = new BufferedImage(ST_WIDTH, ST_HEIGHT,
            BufferedImage.TYPE_INT_RGB);
   private Color color = Color.black;
   private ArrayList<Point> points = new ArrayList<Point>();
   private int colorIndex = 0;

   public STDrawPanel() {
      Graphics g = bImage.getGraphics();
      g.setColor(BACKGROUND_COLOR);
      g.fillRect(0, 0, ST_WIDTH, ST_HEIGHT);
      g.dispose();
   }

   @Override
   protected void paintComponent(Graphics g) {
      super.paintComponent(g);
      g.drawImage(bImage, 0, 0, null);
      Graphics2D g2 = (Graphics2D) g;
      drawCurve(g2);
   }

   private void addCurveToBufferedImage() {
      Graphics2D g2 = bImage.createGraphics();
      drawCurve(g2);
      g2.dispose();
   }

   private void drawCurve(Graphics2D g2) {
      g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
               RenderingHints.VALUE_ANTIALIAS_ON);
      g2.setStroke(STROKE);
      g2.setColor(color);
      if (points != null && points.size() > 1) {
         for (int i = 0; i < points.size() - 1; i++) {
            int x1 = points.get(i).x;
            int y1 = points.get(i).y;
            int x2 = points.get(i + 1).x;
            int y2 = points.get(i + 1).y;
            g2.drawLine(x1, y1, x2, y2);
         }
      }
   }

   @Override
   public Dimension getPreferredSize() {
      return new Dimension(ST_WIDTH, ST_HEIGHT);
   }

   public void curveStart(Point point) {
      points.clear();
      points.add(point);
   }

   public void curveEnd(Point point) {
      points.add(point);
      addCurveToBufferedImage();
      points.clear();
      repaint();

      colorIndex++;
      colorIndex %= colors.length;
      setColor(colors[colorIndex]);
   }

   public void curveAdd(Point point) {
      points.add(point);
      repaint();
   }

   public void setColor(Color color) {
      this.color = color;
   }
}

class STMouseAdapter extends MouseAdapter {
   private STDrawPanel drawPanel;

   public STMouseAdapter(STDrawPanel drawPanel) {
      this.drawPanel = drawPanel;
   }

   @Override
   public void mousePressed(MouseEvent e) {
      drawPanel.curveStart(e.getPoint());
   }

   @Override
   public void mouseReleased(MouseEvent e) {
      drawPanel.curveEnd(e.getPoint());
   }

   @Override
   public void mouseDragged(MouseEvent e) {
      drawPanel.curveAdd(e.getPoint());
   }
}