// Name of the file    :: Clacker.java 
// created by          :: Sridhar Kandukuri
// Date                :: 07/15/98
// Description         :: This program makes use of the Color object of 
//                        java.awt class.
// To compile          :: javac Clacker.java
// To execute          :: appletviewer Clacker.html

// The program simulates the Clacker balls.  A set of 5 balls are hung 
// from a point. The first ball, when dropped from a distance hits the
// second ball, the impact of which travels to the fifth which flies off
// in the direction of impact. It then comes back to hit the fourth ball
// the impact of which sets the first ball in motion

import java.applet.Applet;
import java.awt.*;

public class Clacker extends Applet
{
      private Graphics page;

      // the initial coordinates of the first and fifth balls
      private int xleft = 70;
      private int xright = 170;
      
      // the increment/decrement of the first and fifth balls
      // in the x and y directions
      private int ldx = 5;
      private int rdx = 0;
      private int ldy = 3;
      private int rdy = 0;

      // the initial heights of the balls are contained in these variables
      private int lheigth = 80;
      private int rheigth = 92;
      private int heigth = 100;
      
      public void init()
      {
          setVisible(true);
          page = getGraphics();
      }// init
      
      public void start()
      {
           // select a background
           setBackground(Color.blue);
    
           // activate the XOR mode
           page.setXORMode (getBackground());
          
           
           // color of one ball
           page.setColor(Color.red);
           
           // the thread and the ball
           page.drawLine(130,50,110,heigth-3);
           page.fillOval(100,heigth-3,20,20);
           
           // create a new Color, using another form of Color constructor
           Color GREEN = new Color(0,255,0);
           page.setColor(GREEN);
           
           // the thread and the ball
           page.drawLine(130,50,130,heigth);
           page.fillOval(120,heigth,20,20);
           
           // create a new Color using the float parameters in the
           // constructor
           Color YELLOW = new Color(0,0.5f,0.5f);
           page.setColor(YELLOW);
           
           // the thread and the ball
           page.drawLine(130,50,150,heigth-3);
           page.fillOval(140,heigth-3,20,20);

           // the above 3 balls are the middle balls
           // since they do not change position - they need not be 
           // redrawn again and again

           // infinite loop.
           // keep drawing balls
           do
           {
                draw_balls();
           }while (true);
           
      }    
      
      // the delay funtion, which delays the systems for some time
      // so that the effect of movement of the balls can be seen
      public void delay()
      {
          int isleep  = 200;
          
            try {
                Thread.sleep(isleep);
                }
            catch (Exception e)
                {
                    return;
                }
      } 
      
      public void draw_balls()
      {    
           // create a new Color using the integer form of the constructor
           Color brown = new Color(107,69,38);
           
           page.setColor(brown);
           // the thread and the ball

           page.drawLine(130,50,xleft+5,lheigth);
           page.fillOval(xleft-10,lheigth,20,20);

           // create another color using the integer form of the 
           // constructor - the bits in the integer represent the
           // red, green and blue values of the color
           Color new_color = new Color(123456);
           page.setColor(new_color);
           
           // the thread and the ball
           page.drawLine(130,50,xright-5,rheigth);
           page.fillOval(xright-10,rheigth,20,20);
           
           // on hitting the second ball
           // change the direction of the fifth ball
           // in both the dimensions
           if ( (xleft==90) && (ldx==5) )
           {
               ldx = 0;
               rdx = 5;
               ldy = 0;
               rdy = -3;
               
           }
           
           // when the first ball reaches the left limit,
           // change its direction in both dimensions
           if ( (xleft==70) && (ldx==-5) )
           {
               ldx = 5;
               ldy = 3;
           }
           
           // when the fifth ball hits the fourth ball
           // change the direction of the first ball 
           // in both directions
           if ( (xright==170) && (rdx==-5) )
           {
               ldx = -5;
               rdx = 0;
               ldy = -3;
               rdy = 0;
           }
           
           // when the fifth ball reaches the right limit
           // change its direction in both the directions
           if ( (xright==190) && (rdx==5) )
           {
               rdx = -5;
               rdy = 3;
           }
           
           // call delay - so that the new position of the balls is seen
           delay();
           
           
           // erase the balls by over writing them again
           // this when done in the XOR mode accomplishes the tast
           page.setColor(brown);
           page.drawLine(130,50,xleft+5,lheigth);
           page.fillOval(xleft-10,lheigth,20,20);
           
           page.setColor(new_color);
           page.drawLine(130,50,xright-5,rheigth);
           page.fillOval(xright-10,rheigth,20,20);
           
           // update the values of the new postion of the balls
           xleft += ldx;
           xright += rdx;
           lheigth += ldy;
           rheigth += rdy;
           
      }//end draw_balls

// end class Clacker
}