Building iOS 5 Games: Controllers and Sprites

Feb 6, 2012

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In this chapter you will be introduced to the classes that combine to form the foundation of the game engine. Then, you’ll create the sprite classes that draw and control the game characters on the screen.

This chapter is from the book 

Building iOS 5 Games: Develop and Design

Learn More Buy

Beginning with this chapter, you’ll be dealing with a lot of code. Instead of writing the code from scratch, you can follow along with the completed code by downloading it from the book’s website, www.peachpit.com/iOSGames. While examining the code, it will be useful to identify the key sections and to understand their purpose.

Understanding Controllers

You learned a bit about controllers in the previous chapter. In Raiders, controllers are classes that manage the game flow, and are responsible for rendering scenes and managing sprite objects.

Terms to Play With

Before you delve into the code, you should understand a few gaming and programming terms:

Game Scenes

Games are a lot like movies because they are made up of distinct sections that combine to create the whole. In Raiders (as in movies), these sections will be called scenes, and each scene will have a scene controller.

Examples of common scenes are:

MenuScene—Controls the game’s starting menu in which the player can change settings, choose levels, and start game play
HighScoreScene—Displays the high score tables
Level Scene—Each level in a game has its own numbered scene, such as Level1 Scene, Level2 Scene, and so on.
GameOverScene—Plays when the player loses all his lives

Abstraction

Abstraction is a programming technique that uses a base or parent class to define common characteristics for any child classes. This base class is called an abstract class.

Using a real world object as an example, you might have an abstract class called Door, which has a method called Open. This is logical because all doors must open, but this leaves the implementation of how the door will open to the specific door. For example, a child class called SlidingDoor might have a method called Open, but the implementation would make the door slide.

The benefit of abstraction is that the “blueprint” can include just the parent Door, and the actual implementation or mechanics of that door can be created later.

In Raiders, an abstract class called AbstractSceneController is the base class that all the other scene controllers inherit from. This abstract class allows the game engine to render any scene without knowing the specifics of that scene. It also allows you to use one class to control all the scenes and just “plug in” the required scene at the required time.

Game Controller

Continuing with the movie analogy, the game controller is like a director. It manages which scene is currently active, and also controls game state, scores, game levels, and so on.

In this chapter, the game controller will do only two things:

Manage the active scene
Tell the active scene to render itself

In future chapters, the game controller will be assigned many more functions.

Singleton

Singleton is the name given to a class that has only one running instance of itself. This class is used when you need one object to coordinate actions and resources across the app. Because the app is restricted to one instance of a singleton class, the class’ resources are available on a global level. That is, the instance is available in the same state to all other classes of the app that need it. In Raiders, the GameController is a singleton because it requires the same instance throughout the project.

Singletons are used a lot in modern programming, usually when caching resources or accessing shared resources and code.

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