Creating an Engine for Games for Windows - What is a Game Engine?
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Think about a few different games you like, and try to think of them in terms of how they might be designed under the hood. More importantly, see if you can figure out any common design elements that would apply to all the games. For example, do all the games have a background, a title screen, a geographical map, and background music? If so, it's possible that they are designed around the concept of a game engine. Game engines are particularly useful in situations in which you plan on creating more than one game, and you don't want to have to reinvent the wheel each time around. The idea is that you figure out what common functionality all games use, and you write it once and stick it in the game engine.
Another significant benefit of a game engine for Windows games is that it allows you to hide the messy details of Windows-specific code that doesn't necessarily have anything to do with a game. For example, virtually all the code in the Skeleton application in Appendix C has nothing to do with a game, but it's required of every Windows application. Rather than have you cut and paste this generic code to create a new game, I prefer hiding it in a game engine where you never have to fool with it again. You know it's there, but by not having to look at it, you're free to focus on the more important and fun parts of your game code.
In case you're wondering, there's nothing magical or mysterious about a game engine. A game engine represents an organization of the code for a game so that general application tasks are separated from game-specific tasks. The benefit to the game developer is that you can add features to a game engine that you will be able to reuse in all of your future games. Additionally, using a game engine allows you to simplify the code for your games and focus your attention on the game code that matters most. Once you get accustomed to using a game engine, you'll wonder how games could be created any other way. In reality, most commercial game developers do have their own custom game engines that they've developed over years of learning what common features most games require. Your own game engine will likely improve and expand upon the game engine in this book as you design and develop more demanding games.
Pondering the Role of a Game Engine
It is the responsibility of a game engine to handle the chores of setting up a game, making sure that it runs properly, and then shutting it down. Although it is true that these tasks are required of any program, certain aspects of initializing, running, and cleaning up after games are truly unique to games. Therefore, it is important for a game engine to address the unique needs of games and help make the process of building games around the engine as simple and straightforward as possible. With a well-designed game engine, you'll find that creating a game requires a lot less code than if you had not relied on a game engine. The idea is to develop certain core game routines once, stick them in the game engine, and then never bother with them again unless absolutely necessary. For example, once you've written code to load an image and draw it on the screen, there is never a reason to rewrite the code again. Loading and drawing images is a basic feature required of all game engines.
Note - As time and resources allow, you might choose to optimize certain algorithms within your game engine to help make it run more efficiently. Generally speaking, the first goal is to get a game feature working properly and then worry about optimizing it later as you have time.
 This chapter is from Beginning Game Programming, by Michael Morrison (Sams, ISBN: 0672326590). Check it out at your favorite bookstore today.
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