//  Scott DeRuiter      5/2/02
//  AnimateDerivative.java
//  Animates a series of images

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class AnimateDerivative extends JApplet   
{

 	private Image [] image;
	private int i, pausetime;
	ImagePanel canvas;
	private JButton runit, stopit, faster, slower, onestep;
	private JTextField describeField, numberField;

	public AnimateDerivative ( )   
    	{
		image = new Image [12];
		i = 0; 
		pausetime = 450;
	}

	public void init() 
    	{
		setBackground ( Color.black );
		canvas = new ImagePanel ( );
		getContentPane().add( canvas, BorderLayout.CENTER );

		JPanel left = new JPanel ( new GridLayout ( 5, 1 ) );
		getContentPane().add ( BorderLayout.WEST, left );
		runit = new JButton ( "RUN / RESUME" );
		left.add ( runit );
		runit.addActionListener ( canvas );
		stopit = new JButton ( "STOP" );
		left.add ( stopit );
		stopit.addActionListener ( canvas );
		onestep = new JButton ( "NEXT STEP" );
		left.add ( onestep );
		onestep.addActionListener ( canvas );
		faster = new JButton ( "FASTER" );
		left.add ( faster );
		faster.addActionListener ( canvas );
		slower = new JButton ( "SLOWER" );
		left.add ( slower );
		slower.addActionListener ( canvas );
		JPanel bottom = new JPanel ( );
		getContentPane().add ( BorderLayout.SOUTH, bottom );
		describeField = new JTextField ( "Pause Time in Milliseconds:" );
		describeField.setEditable ( false );
		bottom.add ( describeField );
		numberField = new JTextField ( 8 );
		numberField.setText ( "500" );
		bottom.add ( numberField );

		for ( int i = 0; i < image.length; i++ )   
        	{
			image[i] = getImage ( getDocumentBase ( ), (i + 1) + ".jpg" );
			WaitForImage ( this, image[i] );
		}
	}

	public void WaitForImage ( JApplet component, Image image )   
    	{
		MediaTracker tracker = new MediaTracker ( component );
		try  
        	{
			tracker.addImage ( image, 0 );
			tracker.waitForID ( 0 );
		}
		catch ( InterruptedException e )   
        	{
			e.printStackTrace ( );   
		}
	}

	public Insets getInsets ( ) 
    	{
		return new Insets ( 5, 5, 5, 5 );
	}

	class ImagePanel extends JPanel implements ActionListener, Runnable 
    	{

		private Thread runner;
		private boolean running, justonestep;

		public ImagePanel ( )   
        	{
			justonestep = false;
		}
	
		public void paintComponent ( Graphics g )  
        	{
			super.paintComponent ( g );
			g.drawImage ( image[i], 0, 0, this );
		}

		void startRunning() 
        	{
			if (running)
				return;
			runner = new Thread(this);
			running = true;
			runner.start();
		}
	      
		void stopRunning() 
        	{
			running = false;
		}

		public void run() 
        	{
			runit.setEnabled ( false );
			stopit.setEnabled ( true );

			while ( running )   
            		{
				i++;
				if ( i == 12 )
					i = 0;
				repaint ( );
				if ( justonestep )
					running = false;
				else   
                		{
					Thread.yield();
					Pause ( pausetime );
				}
			}
			justonestep = false;
			running = false;

			runit.setEnabled ( true );
			stopit.setEnabled ( false );
		}

		public void Pause ( int milli )   
        	{
			try   
            		{
				Thread.sleep ( milli );
			}
			catch ( InterruptedException e )   { }
		}
	
		public void actionPerformed ( ActionEvent evt )   
        	{
			String command = evt.getActionCommand ( );
			if ( command.equals ( "RUN / RESUME" ) )
				startRunning ( );
			else if ( command.equals ( "STOP" ) )
				stopRunning ( );
			else if ( command.equals ( "NEXT STEP" ) )   
            		{
				justonestep = true;
				startRunning ( );
			}
			else if ( evt.getSource ( ) == faster && pausetime > 50)    
            		{
				pausetime -= 100;
				numberField.setText ( "" + pausetime );
			}
			else if ( evt.getSource ( ) == slower && pausetime < 1950)     
            		{
				pausetime += 100;
				numberField.setText ( "" + pausetime );
			}
		}
	}
}

(Applet "AnimateDerivative" would be displayed here
if Java were available.)