iPhone Game Development

Game State Manager

A serious video game offers more than just a theater of action holding the game: it has a Main menu that allows the player to set options and start a new game or continue a previous one; a Credits screen that shows the names of all the hardworking people who helped make the game; and if your game doesn’t come with a user manual, perhaps a Help section that gives the player a clue about what he’s supposed to be doing.

Each of these is a game state and represents a separate part of the application code. For instance, the functions and navigation invoked by a player in the Main menu are quite different from those invoked by a player in the Credits screen, so the program logic is a lot different, too. Specifically, in the Main menu, you will likely be drawing a title image and some kind of menu, and listening for player input to select one of the menu options. When you are in the Credits screen, you will be drawing the names of all the people who worked on the game, while listening for player input that will cause your current game state to change from the Credits screen back to the Main menu. And finally, in the Game Play state, you will be rendering the actual game and listening for the player’s input to interact with the game logic.

Each of these game states is responsible for handling player input, rendering to the screen, and providing any application logic that is specific to that state. You might recognize these tasks from our earlier discussion about the main ...