Scribble Applet

//  this applet allows the user to draw by dragging the mouse

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

public class Scribble11 extends Applet
          implements ActionListener, MouseListener, MouseMotionListener
{
    private int lastx;
    private int lasty;
    private Button clearButton;
    private Image drawing;
    private Graphics drawGraph;
    private int width;
    private int height;

//  add the button for clearing the drawing, get the size of the
//  drawing area, and register to listen for mouse events and button
//  presses

    public void init()
    {
        clearButton = new Button("Clear");
        clearButton.addActionListener(this);
        this.add(clearButton);
        width = getSize().width;
        height = getSize().height;
        this.addMouseListener(this);
        this.addMouseMotionListener(this);
    }

//  save the position of the mouse when the user presses the mouse button

    public void mouseClicked(MouseEvent e) { }
    public void mouseEntered(MouseEvent e) { }
    public void mouseExited(MouseEvent e) { }
    public void mousePressed(MouseEvent e)
    {
        lastx = e.getX();
        lasty = e.getY();
    }
    public void mouseReleased(MouseEvent e) { }

//  draw a line from the previous position to the current position when the
//  user drags the mouse. also save the new position of the mouse

    public void mouseDragged(MouseEvent e)
    {
        drawGraph.drawLine(lastx,lasty,e.getX(),e.getY());
        repaint();
        lastx = e.getX();
        lasty = e.getY();
    }
    public void mouseMoved(MouseEvent e) { }

//  clear the display if the user clicks on the 'clear' button

    public void actionPerformed(ActionEvent e)
    {
        if (e.getActionCommand().equals("Clear"))
            clear();
    }

    public void clear()
    {
        drawGraph.clearRect(0,0,width,height);
        drawGraph.drawRect(0,0,width-1,height-1);
        drawGraph.drawRect(1,1,width-3,height-3);
        repaint();
    }

//  override the update method to avoid clearing the applet's display
//  area

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

//  initialize the Image for offscreen drawing if necessary, then
//  transfer the Image to the applet's display area

    public void paint(Graphics g)
    {
        if (drawing == null)
        {
            drawing = createImage(width,height);
            drawGraph = drawing.getGraphics();
            drawGraph.setColor(Color.black);
            drawGraph.drawRect(0,0,width-1,height-1);
            drawGraph.drawRect(1,1,width-3,height-3);
        }
        g.drawImage(drawing,0,0,null);
    }

}