Game Development Reference
In-Depth Information
industrystandard has evolved for your game's genre, do not depart from it without
good reason.
Personal computer keyboards have 110 keys, allowing for very broad user interfaces
indeed. Be sure to assign actions to keys in such a way that the letter printed on the
key becomes a mnemonic for the action, for example, F for flaps or B for brakes.
Players themselves can, if you implement the feature, assign actions to keys, so they
don't have to select those functions with mouse clicks.
KNOBS, SLIDERS, AND PRESSURE-SENSITIVE BUTTONS
You rarely find k nobs (also sometimes called
Pong paddles
for historical reasons)
nowadays, although the mouse wheel functions as a knob. Limited-travel knobs
can move only so far, like a volume knob on a stereo, and return an absolute value.
Unlimited-travel knobs, including the mouse wheel, may be spun continuously and
return relative data. Knobs are generally not self-centering; they stay where the
user puts them. Knobs, especially large ones, offer fine unidimensional control.
TIP
Don't try to
convert a game de-
signed for a knob to
work with a joystick.
The joystick's combi-
nation of limited travel
and self-centering
contradicts the game's
original design. The
arcade game
Tempest
used a large, heavy
knob that could be
spun continuously;
when ported to a
console machine with
a joystick, players
enjoyed the game less
despite the improved
graphics.
A slider is a small handle that moves along a slot in the controller, which constrains
its travel. It returns an absolute position and stays where the player puts it. You find
sliders usually used as adjuncts to joysticks for flight simulators; the slider controls
the throttle for the engine, letting the player set his speed and leave it there.
A few controllers, such as the Nintendo GameCube controller, include analog pres-
sure-sensitive buttons that, instead of transmitting a binary
on
or
off
value, send
a number that indicates how hard the player presses. This gives the player a finer
degree of control than an ordinary binary controller button. The trigger buttons
on the Xbox controller also return analog values. You can think of them as spring-
loaded sliders that return to a zero point when released.
COMPASSES
Like global positioning systems, compasses are mostly useful for augmented reality
games played outdoors. A digital compass returns a single numeric value, the direc-
tion in degrees that a handheld device is facing with respect to true north. If the
player holding it turns the device in a different direction, the compass detects it.
Later versions of the Apple iPhone include a compass.
Navigation Mechanisms
Navigation mechanisms allow the player to tell a character, vehicle, or other mobile
unit how to move. This section uses the term
avatar
to refer to anything that the
player controls directly, including vehicles. It also uses the word
steering
to describe
the act of directly controlling both vehicles and characters, even though the idea of
steering a walking character may sound a little odd. UI designers usually find creat-
ing vehicle navigation systems easier than creating ones for characters because input
devices more closely resemble a vehicle's controls than they do an avatar's body.
