// file:    BaseApplet.java
// author:  Robert Keller
// purpose: Base class for simple applets, with flicker-free graphics

/**  
 * BaseApplet.java
 * @version 1
 * @author  Robert M. Keller
 * $Id*
 */

import java.applet.*;           // applet classes
import java.awt.*;              // Abstract Window Toolkit classes
import java.awt.event.*;

/**
 * BaseApplet with methods intended to be over-ridden to create games, etc.
 */ 

public class BaseApplet extends Applet 
                        implements Runnable, MouseListener, MouseMotionListener, KeyListener
{
protected Color backgroundColor = Color.white,
		foregroundColor = Color.black;

protected int currentDelay = 10;  // default cycle delay in milliseconds

protected Thread myThread;	  // the Thread for this Applet

protected Image image;	          // Image containing the offScreen buffer

protected Graphics offScreen;     // offScreen buffer for flicker-free display


/**
 * Initialize the applet.  Can be over-ridden in a derived class, but
 * if so, the over-riding method should call super.init();.
 */

public void init()
  {
  setBackground(backgroundColor);
  createOffScreenBuffer();
  addMouseListener(this);
  addMouseMotionListener(this);
  addKeyListener(this);
  }


/**
 * Start the applet.  
 * Called when the applet is first started and when the web-page is re-entered.
 */
public void start()
  {
  if( myThread == null )
    {
    myThread = new Thread(this);
    myThread.start();
    }
  }


/**
 * Run the applet by running its thread.
 * This over-rides the run() method in class Applet.
 */

public void run()
  {
  requestFocusInWindow();
  while( continueRunning() )
    {
    step();		// Update the state of the game, including any drawing.
    sleep();		// Wait awhile before the next step.
    }
  }


/**
 * Sleep for the amount specified in current delay.
 */

public void sleep()
  {
  sleep(currentDelay);
  }


/**
 * Sleep for a specified number of milliseconds.
 */

public void sleep(int amount)
  {
  try
    {
    myThread.sleep(amount);
    }
  catch( Exception e )
    {
    }
  }


/**
 * Set the current delay value in milliseconds.
 */

public void setDelay(int delay)
  {
  currentDelay = delay;
  }


/**
 *   Create the off-screen buffer.
 */

void createOffScreenBuffer()
  {
  image = createImage(getWidth(), getHeight());
  offScreen = image.getGraphics();
  }


/**
 *   Clear the off-screen buffer.
 */

public void clearOffScreenBuffer()
  {
  offScreen.setColor(backgroundColor);
  offScreen.fillRect(0, 0, getWidth(), getHeight());
  }



/**
 * update is implicitly called by repaint()
 * It calls paint(Graphics).
 * This method intentionally over-rides update() in class Applet so that
 * the background is not blanked, which will tend to cause flicker.
 *
 * It is probably best not to change this unless you really know what
 * you are doing.
 */

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


/**
 * paint(Graphics) is is called by update(Graphics).
 * This is where the off-screen buffer gets painted to the screen.
 * image contains the Graphics for what is to be painted.
 *
 * It is probably best not to change this unless you really know what
 * you are doing.
 */

public void paint(Graphics g)
  {
  g.drawImage(image, 0, 0, null);
  }


/**
 * Over-ride this in the derived class.  It gives the condition under
 * which the applet will continue calling step in the main loop.
 */

public boolean continueRunning()
  {
  return true;
  }


/**
 * Over-ride this in the derived class.  It indicates what the will be
 * done as a single step in the main loop.
 */

public void step()
  {
  }


/**
 * Paint the off-screen buffer onto the screen
 */

void paintBuffer()
  {
  repaint();
  }


/**
 * These are required for implementing MouseListener. 
 * They can be over-ridden in a derived class at your option.
 */

public void mouseClicked(MouseEvent e)
  {
  }

public void mousePressed(MouseEvent e)
  {
  }

public void mouseReleased(MouseEvent e)
  {
  }

public void mouseEntered(MouseEvent e)
  {
  }

public void mouseExited(MouseEvent e)
  {
  }

/**
 * These are required for implementing MouseMotionListener. 
 * They can be over-ridden in a derived class at your option.
 */

public void mouseMoved(MouseEvent e)
  {
  }

public void mouseDragged(MouseEvent e)
  {
  }

/**
 * These are required for implementing KeyListener. 
 * They can be over-ridden in a derived class at your option.
 */

public void keyTyped(KeyEvent e)
  {
  }

public void keyPressed(KeyEvent e)
  {
  switch( e.getKeyCode() )
    {
    case java.awt.event.KeyEvent.VK_DOWN:   break;
    case java.awt.event.KeyEvent.VK_UP:     break;
    case java.awt.event.KeyEvent.VK_LEFT:   break;
    case java.awt.event.KeyEvent.VK_RIGHT:  break;
    default:  
    }
  }

public void keyReleased(KeyEvent e)
  {
  }

} // BaseApplet