//  AnimationDemoApplet.java  (c) 2006 Kari Laitinen

//  http://www.naturalprogramming.com/

//  2006-10-04  File created.
//  2008-02-03  Last modification.

/*  This Java applet demonstrates how a thread can be used to
    produce animation onto the screen. "Animation" in this program 
    means that there is a blinking ball on the screen.

    There are calls to the System.out.print() method which produce
    text lines into the command prompt window when this
    program is run with AppletViewer. By exploring these text lines
    you can find out how various methods are called when this program
    is executed.

    The init() method is called once when an applet starts executing.

    The stop() method is called always when the applet window is minimized.

    The start() method is called always when the applet window is exposed
    after it has been minimized.

    A NOTE RELATED TO HUMAN PHYSIOLOGY:

    This program can be used to demonstrate the strange 
    behaviour of our sight system. If you watch the blinking ball
    from a short distance, you'll notice that when the ball disappears
    from the screen you see a kind of shadow of the ball. The color
    of the shadowish ball seems to be close to magenta, which is a
    kind of opposite color to cyan, the color of the 'real' ball.
    The reason for seeing this kind of shadow of the ball is in
    our eyes. Our sight system is such that the sight cells inside
    our eyes remember the object (i.e. the ball) that disappears,
    but they produce the opposite color for the disappeared object.
    (This nice feature in this program was discovered by professor
    Matti Weckström from the University of Oulu.)
*/


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

public class AnimationDemoApplet extends JApplet
                                 implements Runnable
{
   int applet_width, applet_height ;

   Thread  animation_thread  =  null ;

   boolean  thread_must_be_executed  =  false ;

   boolean  ball_must_be_shown  =  true ;

   int ball_position_x, ball_position_y ;

   Color  ball_color  =  Color.cyan ;

   public void init()
   {
      applet_width     =  getSize().width ;
      applet_height    =  getSize().height ;
      ball_position_x  =  applet_width / 2  -  40 ;
      ball_position_y  =  applet_height / 2  -  40 ;
      System.out.print( "\n Method init() executed. " ) ;
   }

   public void start()
   {
      if ( animation_thread  ==  null )
      {
         animation_thread  =  new  Thread( this ) ;

         thread_must_be_executed  =  true ;

         animation_thread.start() ;
      }

      System.out.print( "\n Method start() executed. " ) ;
   }

   public void stop()
   {
      if ( animation_thread  !=  null )
      {
         animation_thread.interrupt() ;

         thread_must_be_executed  =  false ;

         animation_thread  =  null ;
      }

      System.out.print( "\n Method stop() executed. " ) ;
   }

   public void run()
   {
      System.out.print( "\n Method run() started." ) ;

      while ( thread_must_be_executed  ==  true )
      {
         System.out.print( " X " ) ;

         try
         {
            Thread.sleep( 1000 ) ;  //  Delay of 1000 milliseconds.
         }
         catch ( InterruptedException  caught_exception )
         {
            thread_must_be_executed  =  false ;
         }

         repaint() ;
      }

      System.out.print( "\n Method run() stopped. " ) ;
   }

   public void paint( Graphics graphics )
   {
      super.paint( graphics ) ;

      if ( ball_must_be_shown  ==  true )
      {
         graphics.setColor( ball_color ) ;

         graphics.fillOval( ball_position_x, ball_position_y, 80, 80 ) ;

         ball_must_be_shown  =  false ;
      }
      else
      {
         ball_must_be_shown  =  true ;
      }

   }
}