Controlling Games with the Keyboard and Mouse - Taking a Look at User Input Devices
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An input device is the physical hardware that allows a user to interact with a game. Input devices all perform the same function: converting information provided by the user into a form understandable by the computer. Input devices establish the link between the user and your game. Even though you can't directly control the input device hardware, you can certainly control how it is interpreted in your game. As I mentioned earlier, there are three primary types of user input devices:
The keyboard
The mouse
Joysticks
Note - In case you're wondering, trackballs are functionally very similar to mouse devices and are often treated just like mouse devices from a software perspective. In fact, the Win32 API doesn't discern between trackballs and mouse devices, so the mouse support in your games indirectly supports trackballs as well. Similarly, game pads are classified as joysticks and are treated no differently than joysticks from a programming perspective.
The next few sections get you acquainted with these devices and their relationship to game user input.
Accepting Keyboard Input
The keyboard has been the computer input device of choice since its inception. Although mouse devices, joysticks, flight sticks, game pads, virtual reality gloves, and many other user input devices have brought extended input capabilities to the game player, none is as established as the keyboard. At the bare minimum, you can always count on a game player having a keyboard.
The keyboard is a surprisingly useful input device for a wide range of games. The sheer number of keys alone gives the keyboard appeal for games that require a wide variety of user input. Even more useful with the keyboard is the natural feel of pressing keys for games requiring quick firing and movement. This usefulness is evident in the number of arcade games that still use buttons, even when powerful digital joysticks are readily available. Keys (or buttons) simply are easier to use in many games, including those with many input combinations.
When assessing the potential use of the keyboard in a game, try to think in terms of the most intuitive user interface possible. For example, any game involving the player moving an object around would benefit from using the arrow keys. A good example is the classic 3D-shooter Doom, which makes creative use of a keyboard-specific feature that greatly enhances the playability of the game. The left and right arrow keys, when used alone, rotate the player left and right in the game world. However, when the Shift key is held down, the same left and right arrow keys cause the player to strafe, meaning that the player moves sideways without changing direction. This seemingly small enhancement to the keyboard controls goes a long way when playing the game.
When you're deciding on specific keys to use for keyboard controls in your game, consider the potential limitations on players using other platforms or hardware configurations. For example, I primarily use a Windows XP PC equipped with a Microsoft Natural keyboard. If you aren't familiar with these keyboards, they are split down the middle for ergonomic reasons. If you don't use one of these keyboards, it might not occur to you that key combinations near the center of the keyboard will be separated a few inches for people like me. So, remember that if you use the G and H keys (or other middle keys) in your game, and it plays well for you, it might not work out so well for players with different keyboards.
Note - In Chapter 1, I mentioned a game called Combat Tanks that I co-developed nearly 10 years ago. Back then, there were no keyboards with split key configurations, so that particular game suffers from keys that are uncomfortably spread out on keyboards such as the Microsoft Natural keyboard. Fortunately, we designed the game with customizable keys, so you can change around the control keys for the game. This is an example of a nice game feature having future unintended significance...always a good thing!
The most common keys used in games are the arrow keys. If you're writing an action game, you might also have keys for firing and selecting between weapons. When you're deciding on the keys to use, keep in mind things such as the creative usage of the Shift key in Doom. If you can limit the number of primary game control keys by making use of a secondary key, such as Shift, you've made the game controls that much easier to use.
Note - Just in case you think I'm a bit behind the times by referring to Doom repeatedly, I realize that numerous newer and better first-person shooters are around now. However, I like to point out which games added a new or unique feature to a genre, and in this case, Doom was the first major game I know of that used the strafing feature for moving from side to side.
 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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