Interface - Designing Games - page 237

creates a mapping from the health indicator to the red button. Note that
this is also a kind of metaphor, since there is a cultural convention that
associates red with health.
Mapping reduces learning burden. It saves players from having to
remember an abstract relationship between button symbols and in-game
actions. This is especially important for less experienced players, so games
geared toward new players sometimes go to extremes to explore new map-
pings. The Wii's motion controller, the Kinect body-sensing system, and
Rock Band 's huge guitar-shaped controller are all examples of expensive
physical interfaces that appeal to casual players by creating new kinds of
extremely close mapping.
CONTROL EXCLUSIVITY is the physical relationships between different
controls and how they can be used in combination.
Depending on the physical relationships between controls and play-
ers' bodies, some pairs of controls cannot be used at the same time. On a
gamepad, there might be two buttons that are both only reachable with the
left index finger. On a motion controller, the player can move their arms
independently, but can't move one arm to signal two different functions
at the same time.
A game must map exclusive controls to actions that are exclusive in
the game. For example, the Xbox 360 controller places both a bumper and
a trigger by each index finger so that it's impossible to press both at once.
In BioShock , the bumper is used to select a weapon, while the trigger is
used to fire it. This makes sense because in the fiction and mechanics,
it's impossible to change weapons and fire at the same time. The physi-
cal controls are exclusive, and they're mapped to game actions that are
exclusive, so there is no conflict. Even better, the exclusivity of the physical
controls emphasizes and naturally teaches the exclusivity of the in-game
mechanics.
When exclusive controls are mapped to nonexclusive actions, frustra-
tion and awkwardness result. Think of any game that puts a tool select on
the Xbox 360 D-Pad and movement on the left stick. Both of these are con-
trolled by the left thumb, which means that players have to stop moving
to change tools. A better design will either find another control to handle
tool changes, or add a restriction into the game that mirrors the restriction
implied by the physical controls.