public CGameState(int num_enemies)
        {
            if (num_enemies > 0)
            {
                Enemies = new CEnemy[num_enemies];
            }

            for (int i = 0; i < num_enemies; i++)
            {
                Enemies[i] = new CEnemy();
            }
        }
        //****************************************************************//
        // This function updates the position of each enemy in the game.  //
        // If it would be in collision with a wall the position is not    //
        // changed.                                                       //
        //****************************************************************//
        private void UpdatePosition(CSprite sprite, float time_delta)
        {
            //////////////////////////////////////////////////////////////////
            // Update a sprite to be in a new position using it's velocity.
            // If it is in a collision, we leave it in current location.
            // however, if it is an enemy we move it to it's target position
            // ready to find a new direction to move into.

            CPoint2f newPos = new CPoint2f();

            newPos.X = sprite.Position.X + time_delta * sprite.Velocity.X;
            newPos.Y = sprite.Position.Y + time_delta * sprite.Velocity.Y;

            bool collisionFire = false;

            if (sprite is CEnemy)
            {
                collisionFire = IsInCollisionWithFire(newPos);
            }

            if (!IsInCollisionWithWall(newPos) && !collisionFire)
            {
                sprite.Position.X = newPos.X;
                sprite.Position.Y = newPos.Y;
            }
            else
            {
                ///////////////////////////////////////////////////////////////
                // See if sprite is an enemy, if so update it's position to be
                // the target position. NOTE: this could make odd behaviour if
                // enemy walks too far!

                if (sprite is CEnemy)
                {
                    CEnemy enemy = (CEnemy)sprite;

                    enemy.Position.X = enemy.TargetPosition.X;
                    enemy.Position.Y = enemy.TargetPosition.Y;
                }
            }
        }