XNA Game Studio 3.0 : Creating Game Components - Adding Game Sounds

Such is the value of sound to a game that even the very first computer games had sound output, even if it took the form of primitive beeps. You now need to think about how sounds can be added to the game. You have seen how easy it is to load and play sound effects; now you have to bind them into the game sprites so that when something happens to each sprite, it plays an appropriate sound effect. But before we can add sounds, we have to decide how to do it and decide who makes the sounds in the game.

This is actually a profound question. Does the BreadAndCheeseGame class make the sound, or do the sprites do it themselves? After some thought, you probably come to the same conclusion that I did, which is that the sound of a sprite is a bit like the texture that is used to draw it; it is a property of the sprite. Furthermore, on the principle of high cohesion being good (that is, it is best if an object can look after itself and not rely on any other objects), it makes sense for the sprite to make the sound. Sprites that need to make sounds can be given the sound effects when they are constructed and play the appropriate ones as required. You can make the sounds any way you like. I created mine using a little electronic sound generator. Figure 1 shows the sounds after I had imported them. Note that the name of each sound file directly reflects its purpose.

Each of them is loaded into the game as content, and the constructor of each sprite class is modified to accept the sound effect resources when the sprite is created:

CheeseBall = new BallSprite(
    Content.Load<Texture2D>("Images/Cheese"),
    0.07f,   // a cheese takes 0.07 of the screen width
    200,     // cheese takes 200 ticks to cross the screen
    minDisplayX, maxDisplayX, minDisplayY, maxDisplayY,
    displayWidth / 4,   // a quarter across the screen
    displayHeight / 4,  // a quarter down the screen
    Content.Load<SoundEffect>("Sounds/BreadHit"),
    Content.Load<SoundEffect>("Sounds/TomatoHit"),
    Content.Load<SoundEffect>("Sounds/EdgeHit"),
    Content.Load<SoundEffect>("Sounds/LoseLife"));
GameSprites.Add(Cheese);

This code creates a new CheeseBall and passes it all the information it needs, including the sound effects. The constructor of the class stores the sound effects so that they can be used to produce the sounds as required:

public BallSprite(Texture2D inSpriteTexture,
    float widthFactor, float ticksToCrossScreen,
    float inMinDisplayX, float inMaxDisplayX,
    float inMinDisplayY, float inMaxDisplayY,
    float inInitialX, float inInitialY,
    SoundEffect inBatHitSound,
    SoundEffect inTargetHitSound,
    SoundEffect inEdgeHitSound,
    SoundEffect inLoseLifeSound)
    : base(inSpriteTexture, widthFactor, ticksToCrossScreen,
        inMinDisplayX, inMaxDisplayX,
        inMinDisplayY, inMaxDisplayY,
    inInitialX, inInitialY)
{
    batHitSound = inBatHitSound;
    targetHitSound = inTargetHitSound;
    edgeHitSound = inEdgeHitSound;
    loseLifeSound = inLoseLifeSound;
}

This code actually looks rather horrible, and for that I apologize. The constructor for the cheese actually does very little work because most of the heavy lifting is done by its base constructor, which sets up the moving sprite. All the constructor does is copy the incoming sound effects into members inside the BallSprite class, so that they can be used in the Update method to make the appropriate sounds. I think it is fair to say that when you understand this lump of code, you properly understand constructors and class hierarchies.

Here is part of the Update method in the BallSprite class that plays a sound when the cheese ball hits the top of the screen:

if (y <= minDisplayY)
{
    // ball has hit the top of the screen.
    edgeHitSound.Play();
    ySpeed = Math.Abs(ySpeed);

Note:

The game will run on a Zune but because the Zune has fewer sound channels than the Xbox or Windows PC it may fail when the bat or the ball collides with a large number of killer tangerines. This is because the game will try to play a sound for each collision, and these are all played on separate sound channels. To fix this problem you could make a Zune version that does not play a new collision sound if the existing one is already active. I will leave this for you to sort out.