// ------------------------------------------------------
// Using Directives
// ------------------------------------------------------

using System;
using System.Drawing;
using System.Windows.Forms;

// ------------------------------------------------------
// BallForm
// ------------------------------------------------------

public class BallForm : Form
{
   public BallForm()
   {
      // ------------------------------------------------------
      // Give our ball an initial location and speed
      // ------------------------------------------------------

      mBallX      = GetX();
      mBallY      = GetY();
      mBallXSpeed = GetSpeed();
      mBallYSpeed = GetSpeed();

      // ------------------------------------------------------
      // Set up our timer and our form
      // ------------------------------------------------------

      mMoveBallTimer.Enabled  = true;
      mMoveBallTimer.Interval = 10;
      mMoveBallTimer.Tick    += new System.EventHandler(MoveBallTick);

      // ------------------------------------------------------
      // Use double buffering for reducing flicker
      // ------------------------------------------------------

      Size            = new Size(FORM_WIDTH, FORM_HEIGHT);
      FormBorderStyle = FormBorderStyle.Fixed3D;
      Text            = "Bouncing Ball";
      Paint          += new PaintEventHandler(RenderBall);

      SetStyle(
         ControlStyles.AllPaintingInWmPaint |
         ControlStyles.UserPaint |
         ControlStyles.DoubleBuffer,
         true
      );

      UpdateStyles();
   }

   // ------------------------------------------------------
   // Get a random: 'speed', 'x' or 'y' location
   // ------------------------------------------------------

   private int GetSpeed()
   {
      return(mRandom.Next(MIN_SPEED, MAX_SPEED));
   }

   private int GetX()
   {
      return(mRandom.Next(0, ClientSize.Width - BALL_WIDTH));
   }

   private int GetY()
   {
      return(mRandom.Next(0, ClientSize.Height - BALL_HEIGHT));
   }

   // ------------------------------------------------------
   // MoveBallTick - Update the ball's location
   //                and handle collisions
   // ------------------------------------------------------

   private void MoveBallTick(object sender, EventArgs e)
   {
       mBallX += mBallXSpeed;

       if (mBallX < 0 || mBallX + BALL_WIDTH > ClientSize.Width)
           mBallXSpeed = -mBallXSpeed;

       mBallY += mBallYSpeed;

       if (mBallY < 0 || mBallY + BALL_HEIGHT > ClientSize.Height)
           mBallYSpeed = -mBallYSpeed;

       Refresh();
   }

   // ------------------------------------------------------
   // RenderBall - Draw the ball at its current location
   // ------------------------------------------------------

   private void RenderBall(object sender, PaintEventArgs e)
   {
      e.Graphics.Clear(BackColor);

      e.Graphics.FillEllipse(
         Brushes.Blue, mBallX, mBallY, BALL_WIDTH, BALL_HEIGHT
      );

      e.Graphics.DrawEllipse(
         Pens.Black, mBallX, mBallY, BALL_WIDTH, BALL_HEIGHT
      );
   }

   // ------------------------------------------------------
   // Settings
   // ------------------------------------------------------

   private const int FORM_WIDTH  = 500;
   private const int FORM_HEIGHT = 500;
   private const int MIN_SPEED   = 1;
   private const int MAX_SPEED   = 5;
   private const int BALL_WIDTH  = 25;
   private const int BALL_HEIGHT = 25;

   // ------------------------------------------------------
   // Member variables
   // ------------------------------------------------------

   private Random mRandom        = new Random();
   private Timer  mMoveBallTimer = new System.Windows.Forms.Timer();
   private int    mBallX;
   private int    mBallY;
   private int    mBallXSpeed;
   private int    mBallYSpeed;

   // ------------------------------------------------------
   // Main
   // ------------------------------------------------------

   [STAThread]

   static void Main()
   {
      Application.Run(new BallForm());
   }
}