FUNDAMENTALS OF GAME DESIGN, SECOND EDITION
Terminology
The following discussion uses the game industry's standard terminology for the kinds of data that control devices send to the processor as the result of player inputs. You may find some familiar terms that nevertheless require explanation, because the game industry uses those terms in ways that may differ from what you're used to.
Most input devices—the mouse being a notable exception—default to a neutral position. To send a signal to the game, the user must push, pull, grasp, or press the device to deflect it, and a spring-loaded mechanism returns it to the neutral position when the player releases the device. Joysticks and D-pads return to center; buttons and keys return to the off state.
A device that can return only two specific signals is called a binary device, the signals generally being interpreted as off and on. Another common kind of input device transmits a value from a range of many possible values and the industry, for historical reasons, calls these analog devices. Any game control device can be classed as either analog or binary, though all of the technology is digital.
Don't confuse the type of data (binary or analog) with the dimensionality of the device. A one-dimensional device transmits one datum, and a two-dimensional device transmits two data, and so on, regardless of whether they transmit binary or analog data.
A device that returns data about its current position as measured from the neutral position provides absolute values. Such a device—a joystick, for example—can travel only a limited distance in any direction, and so it transmits values in a range from zero to its maximum.
Other devices offer effectively unlimited travel and have no neutral position. These return relative values, that is, the relative distance that the device has traveled from its previous position. Mouse wheels and track balls are examples; the player may rotate them indefinitely.
