using System;
using System.Drawing;
using System.Collections;

/// <summary>
///object to be animated for the Balls program
/// </summary>

public class Ball
{  public Color color;
   public int x,y;   // position of center
   public int p,q;   // x and y velocities;
   public int r;     // radius of ball
   public int mass;  // needed if we someday want to make the balls collide with each other

	public Ball(Color c, int X, int Y, int xVelocity, int yVelocity, int radius)
	{ color = c;
	  x = X;
	  y = Y;
	  p = xVelocity;
	  q = yVelocity;
	  r = radius;
	}

	public void Draw(Graphics g)
	{ Brush b = new SolidBrush(color); 
	  Rectangle rect = new Rectangle(x-r, y - r, 2*r,2*r);
	  g.FillEllipse(b,rect);  
	}

public void Bounce(int t, Rectangle box)
{ // update position and velocity, including bouncing off the walls of box
      x = (int)(x + p*t/1000.0F);
      y = (int)(y + q*t/1000.0F);
      int oops = x + r - box.Right;
      if(oops > 0) 
	      { x -= oops;  // bounce off right wall
		 p = -p;
	      }
      oops = r - x;
      if(oops > 0)
	      { x += oops;
		 p = -p;
	      }
      oops = y + r - box.Bottom;
      if(oops> 0)
	      { y -= oops;
		 q = -q;
	      }
      oops = r-y;
      if(oops > 0)
	      { y += oops;
		 q = -q;
	      }
}

/*  A challenge to my A+ students:  Implement this and make the balls bounce off 
of each other as well as the walls  */

private void Collide(ref Ball u, ref Ball v)
{  int M = u.mass;
   int m = v.mass;

}   


public static void UpdateBalls(ArrayList balls, int t, Rectangle box)
// update positions and velocities of all the balls to 
// reflect the passage of time t (in milliseconds)
{ foreach(Ball b in balls)
  { 
    b.Bounce(t,box);
  }
}
}