How to draw thin line with no gap while dragging the cursor?

问题

I have this following class, which refresh a jpeg file in layer 0 and layer 1 is used to draw/paint/sketch up anything related to smash things. But in my drawing when I want to do a thin line, it breaks. Because the mouse cursor movement needs to be slower.

How to resolve on fast mouse move, that the line remains joined?

Annotation.java

package test;

import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Annotation {

  // Image
  private static Image backgroundImage;
  private static BufferedImage _bufImage = null;

  // Enum 
  public  static enum Shape { RECTANGLE, OVAL, LINE }
  private static enum State { IDLE, DRAGGING }       

  private static final Shape INIIIAL_SHAPE = Shape.RECTANGLE;
  private static final Color INITIAL_COLOR = Color.RED;  
  private static Shape _shape = INIIIAL_SHAPE;
  private static Color _color = INITIAL_COLOR;

  private static State _state = State.IDLE;
  private static Point _start = null; 
  private static Point _end   = null;

  // JPanel
  private static JPanel p;
  private static JPanel mp;

  /* Run: */
  public static void main(String args[]) {   
    c();
  }

  /* GUI */
  public static void c() {      
    try {
      backgroundImage = ImageIO.read(new File("/var/tmp/test.jpeg"));
    } catch (IOException e) {
      e.printStackTrace();
    }

    myTimer();
    loadAnnotation();
    loadBackground();

    JFrame f; 
    f = new JFrame();    
    f.setLayout(new BorderLayout());
    f.add(mp);
    f.pack();
    f.setVisible(true);    
  }

  /* 5 seconds to load picture */
  public static void myTimer() {   
    javax.swing.Timer t = new javax.swing.Timer(5000, new ActionListener() {
      public void actionPerformed(ActionEvent ae) {
        try {
          backgroundImage = ImageIO.read(new File("/var/tmp/test.jpeg"));    
          mp.repaint();
        } catch (IOException e) {
          e.printStackTrace();
        }
      }
    });
    t.start();
  }

  /* Layer 0: 
   * Load background picture */
  public static void loadBackground() {    
    mp = new JPanel() {
      public void paintComponent(Graphics g) {       
        super.paintComponent(g);
        g.drawImage(backgroundImage, 0, 0, 1024, 600, null);            
      }
      public Dimension getPreferredSize() {
        return new Dimension(1024, 600);
      }
    };    
    mp.add(p);        
  }

  /* Layer 1: 
   * Annotation: Draw on top of background picture anything! */
  public static void loadAnnotation() {

    p = new JPanel() {
      public void paintComponent(Graphics g) {       
        Graphics2D g2 = (Graphics2D)g;
        g2.setColor(Color.RED);
        if (_bufImage == null) {        
            int w = this.getWidth();
            int h = this.getHeight();
            _bufImage  = new BufferedImage(1024,600, BufferedImage.TRANSLUCENT);
            Graphics2D gc = _bufImage.createGraphics();
        }

        g2.drawImage(_bufImage, null, 0, 0);        
        if (_state == State.DRAGGING) {
          g2.drawLine(_start.x, _start.y, _end.x  , _end.y);
        }        
      }

      public Dimension getPreferredSize() {
        return new Dimension(1024, 600);
      }      
    };

    p.setLayout(new FlowLayout());
    p.addMouseListener(new MouseListener() {
      @Override
      public void mouseClicked(MouseEvent me) {
      }

      @Override
      public void mousePressed(MouseEvent me) {
      }

      @Override
      public void mouseReleased(MouseEvent me) {
        //_state = State.IDLE;
        _state = State.IDLE;
      }

      @Override
      public void mouseEntered(MouseEvent me) {
      }

      @Override
      public void mouseExited(MouseEvent me) {
      }
    });

    p.addMouseMotionListener(new MouseMotionListener() {

      @Override
      public void mouseDragged(MouseEvent me) {
        System.out.println("drag");        
        _state = State.DRAGGING; 
        _start = me.getPoint();
        _end   = _start;
        if (_state == State.DRAGGING) {
            Graphics2D g2 = _bufImage.createGraphics();
            g2.setColor(Color.red);
            g2.setStroke(new BasicStroke(90));   
            g2.fillOval(_start.x, _start.y, 10, 10);            
            p.repaint();                        
        }         
      }

      @Override
      public void mouseMoved(MouseEvent me) {
        System.out.println("move");
      }
    });

    JButton pm = new JButton("+");
    pm.addActionListener(new ActionListener() {
      @Override
      public void actionPerformed(ActionEvent ae) {
      }
    });    
    p.add(pm);       
    p.setOpaque(true);    
  }

}

回答1:

import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import java.net.URL;
import javax.imageio.ImageIO;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Annotation {

  // Image
  private static Image backgroundImage;
  private static BufferedImage _bufImage = null;

  // Enum
  public  static enum Shape { RECTANGLE, OVAL, LINE }
  private static enum State { IDLE, DRAGGING }

  private static final Shape INIIIAL_SHAPE = Shape.RECTANGLE;
  private static final Color INITIAL_COLOR = Color.RED;
  private static Shape _shape = INIIIAL_SHAPE;
  private static Color _color = INITIAL_COLOR;

  private static State _state = State.IDLE;
  private static Point _start = null;
  private static Point _end   = null;

  // JPanel
  private static JPanel p;
  private static JPanel mp;

  /* Run: */
  public static void main(String args[]) {
    c();
  }

  /* GUI */
  public static void c() {
    try {
        URL url = new URL("http://pscode.org/media/stromlo2.jpg");
      backgroundImage = ImageIO.read(url);
    } catch (Exception e) {
      e.printStackTrace();
    }

    loadAnnotation();
    loadBackground();

    JFrame f;
    f = new JFrame();
    f.setLayout(new BorderLayout());
    f.add(mp);
    f.pack();
    f.setVisible(true);
  }

  /* Layer 0:
   * Load background picture */
  public static void loadBackground() {
    mp = new JPanel() {
      public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawImage(backgroundImage, 0, 0, getWidth(), getHeight(), null);
      }
      public Dimension getPreferredSize() {
        return new Dimension(backgroundImage.getWidth(this), backgroundImage.getHeight(this));
      }
    };
    mp.add(p);
  }

  /* Layer 1:
   * Annotation: Draw on top of background picture anything! */
  public static void loadAnnotation() {

    p = new JPanel() {
      public void paintComponent(Graphics g) {
        Graphics2D g2 = (Graphics2D)g;
        g2.setColor(Color.RED);
        if (_bufImage == null) {
            int w = this.getWidth();
            int h = this.getHeight();
            _bufImage  = new BufferedImage(1024,600, BufferedImage.TRANSLUCENT);
            Graphics2D gc = _bufImage.createGraphics();
        }

        g2.drawImage(_bufImage, null, 0, 0);
        if (_state == State.DRAGGING) {
          g2.drawLine(_start.x, _start.y, _end.x  , _end.y);
        }
      }

      public Dimension getPreferredSize() {
        return new Dimension(1024, 600);
      }
    };

    p.setLayout(new FlowLayout());
    p.addMouseListener(new MouseListener() {
      @Override
      public void mouseClicked(MouseEvent me) {
      }

      @Override
      public void mousePressed(MouseEvent me) {
      }

      @Override
      public void mouseReleased(MouseEvent me) {
        //_state = State.IDLE;
        _state = State.IDLE;
      }

      @Override
      public void mouseEntered(MouseEvent me) {
      }

      @Override
      public void mouseExited(MouseEvent me) {
      }
    });

    p.addMouseMotionListener(new MouseMotionListener() {

      @Override
      public void mouseDragged(MouseEvent me) {
        _state = State.DRAGGING;
        _end   = me.getPoint();
        if (_state == State.DRAGGING) {
            Graphics2D g2 = _bufImage.createGraphics();
            g2.setColor(Color.red);
            g2.setStroke(new BasicStroke(2));
            g2.drawLine(_start.x, _start.y, _end.x, _end.y);
            p.repaint();
        }
        _start = _end;
      }

      @Override
      public void mouseMoved(MouseEvent me) {
        //System.out.println("move");
        _start = me.getPoint();
      }
    });

    JButton pm = new JButton("+");
    pm.addActionListener(new ActionListener() {
      @Override
      public void actionPerformed(ActionEvent ae) {
      }
    });
    p.add(pm);
    p.setOpaque(true);
  }

}

回答2:

I solved this problem by drawing rectangles between points, using the Stroke size (Basic Stroke) for height. It sounds like an icky solution but it does pretty well in reality

来源：https://stackoverflow.com/questions/10388456/how-to-draw-thin-line-with-no-gap-while-dragging-the-cursor

标签

java

image

swing

graphics2d