Step 5: Upward Bullets Too

• Let's make bullets fly upward from the bottom of the screen as well.
• Add a _isMovingDownward boolean variable to the Bullet class that designates whether it moves up or down, and update CheckBounds accordingly:

void CheckBounds()
{
    Vector2f gameSize = (Vector2f)Stage.Game.Graphics.Size;
    Vector2f mySize = (Vector2f)_sprite.Size;

    // tell our containing scene to get rid of us when we are fully out of bounds
    if(_isMovingDownward && Y < -mySize.Y * 0.5f)
        Stage.Remove(this);
    else if(!_isMovingDownward && Y > gameSize.Y + mySize.Y * 0.5f)
        Stage.Remove(this);
}

• Add a new bool parameter to Bullet's constructor so that GameStage can choose to create either a downward-moving or upward-moving bullet:

// constructor
public Bullet(bool movingDownward)
{
    _moveSpeed = Mathf.Random(30.0f, 40.0f);
    _isMovingDownward = movingDownward;
}

• Flip the bullet's sprite vertically in OnLoadGraphics if it's moving upwards:

if(!_isMovingDownward)
    _sprite.FlipY = true;

• In GameStage.cs we'll now create 2 bullets each time instead of one:

// create a bullet moving downward
Vector2f bulletPos = new Vector2f(Mathf.Random(PADDING, Graphics.Width - PADDING), Graphics.Height + PADDING);
Bullet bullet = Add(new Bullet(true), 1);
bullet.Position = bulletPos;

// create a bullet moving upward
bulletPos = new Vector2f(Mathf.Random(PADDING, Graphics.Width - PADDING), -PADDING);
bullet = Add(new Bullet(false), 1);
bullet.Position = bulletPos;

Now the player's caught in a harmless crossfire.

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