Thread: Canvas and MouseListener...

Hi guys,

Here is my code:

public class drawing extends Canvas implements MouseListener, MouseMotionListener {
 
	private int x, y;
 
	public drawing() {
		setBackground(Color.WHITE);
		addMouseListener(this);
		addMouseMotionListener(this);
	}
 
	public void paint(Graphics g) {
		Graphics2D g2 = (Graphics2D) g;
		g2.setColor(Color.BLACK);
		g2.setStroke(new BasicStroke(1.5f));
		g2.drawLine(x, y, x, y);
	}
 
	public void mouseClicked(MouseEvent e) {}
	public void mousePressed(MouseEvent e) {
		x = e.getX();
        y = e.getY();
        paint(this.getGraphics());
	}
 
	public void mouseEntered(MouseEvent e) {}
	public void mouseExited(MouseEvent e) {}
	public void mouseDragged(MouseEvent e) {		
		x = e.getX();
		y = e.getY();
		paint(this.getGraphics());
	}
 
	public void mouseMoved(MouseEvent e) {}
	public void mouseReleased(MouseEvent e) {}
}

I would like to draw with Pencil and the line should be continuous. But when I use this code, fastly motion mouse cause something like that:

obrazek.jpg

How can I resolve it?

Thanks for your responses!

Class names begin with capital letters.

Use Swing to do your painting, study this whole lesson, including the comparison of painting in AWT and painting in Swing.

--- Update ---

Class names begin with capital letters.

Use Swing to do your painting, study this whole lesson, including the comparison of painting in AWT and painting in Swing.

Comment your code.

public class Drawing extends JPanel implements MouseListener, MouseMotionListener {
 
	private int x, y;
 
	ArrayList<Point> Points = new ArrayList<Point>();
 
	public Drawing() {
		setBackground(Color.WHITE);
		addMouseListener(this);
		addMouseMotionListener(this);
	}
 
	 public void paintComponent(Graphics g) {
         super.paintComponent(g);
        // g.fillRect(10,10,100,50);
        // g.drawRect(10,80,100,50);
 
	        Color colour = GUI.getColour();
			g.setColor(colour);
			((Graphics2D) g).setStroke(new BasicStroke(2));
			for(Point p : Points)
			g.drawLine(p.x, p.y, p.x, p.y);
      }
 
	@Override
	public void mouseDragged(MouseEvent arg0) {
		// TODO Auto-generated method stub
		x = arg0.getX();
        y = arg0.getY();
        Points.add(new Point());
        paintComponent(this.getGraphics());
	}
 
	@Override
	public void mouseMoved(MouseEvent arg0) {
		// TODO Auto-generated method stub
 
	}
 
	@Override
	public void mouseClicked(MouseEvent arg0) {
		// TODO Auto-generated method stub
 
	}
 
	@Override
	public void mouseEntered(MouseEvent arg0) {
		// TODO Auto-generated method stub
 
	}
 
	@Override
	public void mouseExited(MouseEvent arg0) {
		// TODO Auto-generated method stub
		x = arg0.getX();
        y = arg0.getY();
        Points.add(new Point());
        paintComponent(this.getGraphics());
	}
 
	@Override
	public void mousePressed(MouseEvent arg0) {
		// TODO Auto-generated method stub
		x = arg0.getX();
        y = arg0.getY();
        Points.add(new Point());
        paintComponent(this.getGraphics());
	}
 
	@Override
	public void mouseReleased(MouseEvent arg0) {
		// TODO Auto-generated method stub
		x = arg0.getX();
        y = arg0.getY();
        Points.add(new Point());
        paintComponent(this.getGraphics());
	}
}

Ok guys, I changed Canvas to JPanel (SWING). My code does not work anymore.

My code does not work anymore.

Please describe "does not work." Are you getting errors? Does the code not perform as desired? Be specific, and ask specific questions.

You've made some positive changes. You're on the right track.

What is GUI?

GregBrannon, it compiles, but does not draw anything.
GUI is another class with GUI implemented. Colouring worked good with javax.awt.Canvas, so I suspect it still works.

Well, without seeing what you're trying to run, one can't tell what needs to be fixed. However, I've taken your code, modified it a bit (mods should have comments), and and added some code of my own to make it "go". Hope this helps, but since I don't know what you needed help with, I can't be sure.

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.util.ArrayList;
 
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
 
public class TestClass2 extends JPanel implements MouseListener, MouseMotionListener {
 
    private int x, y;
 
    ArrayList<Point> Points = new ArrayList<Point>();
 
    public TestClass2()
    {
        setBackground(Color.WHITE);
        addMouseListener(this);
        addMouseMotionListener(this);
 
        // GB: set the preferred size that will be used when the frame
        // is packed
        setPreferredSize( new Dimension( 400, 400 ) );
    }
 
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
 
        // GB: uncommented this code
        g.fillRect(10,10,100,50);
        g.drawRect(10,80,100,50);
 
        // GB: changed this to a constant since GUI is not available
        Color colour = Color.RED;
        g.setColor(colour);
        ((Graphics2D) g).setStroke(new BasicStroke(2));
        for(Point p : Points)
            g.drawLine(p.x, p.y, p.x, p.y);
    }
 
    @Override
    public void mouseDragged(MouseEvent arg0) {
 
        // GB: test code to check event handling
        System.out.println( "In mouseDragged() method." );
        // TODO Auto-generated method stub
        x = arg0.getX();
        y = arg0.getY();
        Points.add(new Point());
        paintComponent(this.getGraphics());
    }
 
    @Override
    public void mouseMoved(MouseEvent arg0) {
 
        // GB: test code to check event handling
        System.out.println( "In mouseMoved() method." );
        // TODO Auto-generated method stub
 
    }
 
    @Override
    public void mouseClicked(MouseEvent arg0) {
 
        // GB: test code to check event handling
        System.out.println( "In mouseClicked() method." );
        // TODO Auto-generated method stub
 
    }
 
    @Override
    public void mouseEntered(MouseEvent arg0) {
 
        // GB: test code to check event handling
        System.out.println( "In mouseEntered() method." );
        // TODO Auto-generated method stub
 
        repaint();
    }
 
    @Override
    public void mouseExited(MouseEvent arg0) {
        // TODO Auto-generated method stub
        x = arg0.getX();
        y = arg0.getY();
        Points.add(new Point());
 
        // GB: these calls aren't necessary
        // paintComponent(this.getGraphics());
 
        repaint();
    }
 
    @Override
    public void mousePressed(MouseEvent arg0) {
        // TODO Auto-generated method stub
        x = arg0.getX();
        y = arg0.getY();
        Points.add(new Point());
 
        // GB: these calls aren't necessary
        // paintComponent(this.getGraphics());
 
        repaint();
    }
 
    @Override
    public void mouseReleased(MouseEvent arg0) {
        // TODO Auto-generated method stub
        x = arg0.getX();
        y = arg0.getY();
        Points.add(new Point());
 
        // GB: these calls aren't necessary, use repaint() if needed
        // paintComponent(this.getGraphics());
 
        repaint();
    }
 
    // added a main() method to run your code on the EDT in a JFrame
    static public void main( String[] args )
    {
        SwingUtilities.invokeLater( new Runnable()
        {
            public void run()
            {
                // creates a frame, adds your JPanel to it and displays it
                JFrame frame = new JFrame( "Test Window" );
                frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
                frame.add( new TestClass2() );
                frame.pack();
                frame.setVisible( true );
            }
        });
    }
}

GregBrannon, thank you!
Look, I added x, y to Points.add(new Point(x, y)); method and it draws.
Try this code and look, what I ment.

It draws such as in MS Paint, but fast mouse motion cause leaving empty fields. And I have a weird "refresh" while painting. How can I solve it?
Thanks for all your responses! I am very grateful!

Here is the code:

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.util.ArrayList;
 
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
 
public class TestClass2 extends JPanel implements MouseListener, MouseMotionListener {
 
    private int x, y;
 
    ArrayList<Point> Points = new ArrayList<Point>();
 
    public TestClass2()
    {
        setBackground(Color.WHITE);
        addMouseListener(this);
        addMouseMotionListener(this);
 
        // GB: set the preferred size that will be used when the frame
        // is packed
        setPreferredSize( new Dimension( 400, 400 ) );
    }
 
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
 
        // GB: uncommented this code
        g.fillRect(10,10,100,50);
        g.drawRect(10,80,100,50);
 
        // GB: changed this to a constant since GUI is not available
        Color colour = Color.RED;
        g.setColor(colour);
        ((Graphics2D) g).setStroke(new BasicStroke(2));
        for(Point p : Points)
            g.drawLine(p.x, p.y, p.x, p.y);
    }
 
    @Override
    public void mouseDragged(MouseEvent arg0) {
 
        // GB: test code to check event handling
        System.out.println( "In mouseDragged() method." );
        // TODO Auto-generated method stub
        x = arg0.getX();
        y = arg0.getY();
        Points.add(new Point(x, y));
        paintComponent(this.getGraphics());
    }
 
    @Override
    public void mouseMoved(MouseEvent arg0) {
 
        // GB: test code to check event handling
        System.out.println( "In mouseMoved() method." );
        // TODO Auto-generated method stub
 
    }
 
    @Override
    public void mouseClicked(MouseEvent arg0) {
 
        // GB: test code to check event handling
        System.out.println( "In mouseClicked() method." );
        // TODO Auto-generated method stub
 
    }
 
    @Override
    public void mouseEntered(MouseEvent arg0) {
 
        // GB: test code to check event handling
        System.out.println( "In mouseEntered() method." );
        // TODO Auto-generated method stub
 
        repaint();
    }
 
    @Override
    public void mouseExited(MouseEvent arg0) {
        // TODO Auto-generated method stub
        x = arg0.getX();
        y = arg0.getY();
        Points.add(new Point(x, y));
 
        // GB: these calls aren't necessary
        // paintComponent(this.getGraphics());
 
        repaint();
    }
 
    @Override
    public void mousePressed(MouseEvent arg0) {
        // TODO Auto-generated method stub
        x = arg0.getX();
        y = arg0.getY();
        Points.add(new Point(x, y));
 
        // GB: these calls aren't necessary
        // paintComponent(this.getGraphics());
 
        repaint();
    }
 
    @Override
    public void mouseReleased(MouseEvent arg0) {
        // TODO Auto-generated method stub
        x = arg0.getX();
        y = arg0.getY();
        Points.add(new Point(x, y));
 
        // GB: these calls aren't necessary, use repaint() if needed
        // paintComponent(this.getGraphics());
 
        repaint();
    }
 
    // added a main() method to run your code on the EDT in a JFrame
    static public void main( String[] args )
    {
        SwingUtilities.invokeLater( new Runnable()
        {
            public void run()
            {
                // creates a frame, adds your JPanel to it and displays it
                JFrame frame = new JFrame( "Test Window" );
                frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
                frame.add( new TestClass2() );
                frame.pack();
                frame.setVisible( true );
            }
        });
    }
}

You should never call

paintComponent(this.getGraphics());

manually. This method is supposed to be called from the renderer of swing. Instead of calling this method yourself simply call repaint(); in your mouseDragged method.
If you call repaint you signal to the renderer that your component needs to be painted again. This will be done in the next rendering cycle.

Cornix, thank you! "Refreshes" disappeared. But empty fields are still there while fast painting.

I dont really know what you mean by that, maybe you can show a screenshot of this behavior?

Cornix,
obrazek.jpg

Well, look at your own code:

        for(Point p : Points)
            g.drawLine(p.x, p.y, p.x, p.y);

What do you think those lines look like?
You draw a line from each point to itself. This means that you are practically drawing points.
You have to always connect 2 points to each other.
1 -> 2
2 -> 3
3 -> 4
...

Cornix,

for(int i=0; Points.contains(i); ++i)
g.drawLine(Points.get(i).x, Points.get(i).y, Points.get(i+1).x, Points.get(i+1).y);

I added this code, it compiles without errors and warnings, but it does not draw anything. :/

Norm, yes, after mouse motion I add a new Point to ArrayList. So it should be true for these objects.

Originally Posted by Norm

Please explain how it will be true. Why will Points contain the value of i?

It should contain 'new Point(x, y)' objects, which I have added e.g in this method:

public void mousePressed(MouseEvent arg0) {
		// TODO Auto-generated method stub
		x = arg0.getX();
        y = arg0.getY();
        Points.add(new Point(x, y));
        //paintComponent(this.getGraphics());
        repaint();
}

Norm, exactly. It should look at all of the points.

And thanks for you all pieces of advice.

Originally Posted by Norm

Following for other Mods:
This seems like a hole in the java compiler's testing. Why isn't contains(i) flagged as an error?
The statement: add(i) will be flagged as an error, but it is symmetrical with contains(i).
Why be able to test if a list contains something if that something can not be added?

The add method of collections takes a generic typed parameter. The contains method takes Object.
I assume that the OP uses a compiler that automatically casts int i to Integer.valueOf(i). The resulting Integer is an Object and can be used as an argument to contains, but not to add since the add method would require a Point object in this specific case.

Thank you guys for all your tips! I have solved the problem.
The correct code for a loop is:

for(int i=0; i<Points.size()-1; i++) {
				Point p1, p2 = null;
				p1 = Points.get(i);
				p2 = Points.get(i+1);
				g.drawLine(p1.x, p1.y, p2.x, p2.y);
			}

Thanks for all your responses! I am very grateful!

Guys, another problem has occured...

It draws excatly, how I wanted, but now when I stop drawing, and start in another place, last point from 'previous' point connects with new Point from 'new drawing'.
I just want to draw with pencil, such how it is in MS Paint.

Thank you guys for all!