Progression Mechanisms - Game Mechanics: Advanced Game Design - page 260

Progress as a Resource
To measure progress in terms of the game's state rather than in terms of the play-
er's location, it's best to treat progress as a resource in its own right. This offers you
many more opportunities to create interactions between the player's progress and
other mechanics in the game. Experience points and character levels are classic
examples from role-playing games; they're numbers that not only tell the player
how he's doing but also can be used for internal computations. (Many RPGs include
weapons that are available only to characters above a certain level, for example.)

NOTE most role-
playing games don't
let their players trade
or otherwise manipu-
late experience points,
but experience points
are absolutely central
to the game, figuring
in all sorts of calcula-
tions—they are simply a
resource that the player
cannot directly modify.
if the idea of progress
as a resource seems
strange, think of it in
terms of experience
points. (depending on
the game, they need
not be visible to the
player.)

You can let players trade their progress points away for some long-term benefit
that will help them progress faster. If the object of a game is to be the first to earn
a stated amount of money, smart players might invest their money (thus appar-
ently losing progress) in schemes that will earn new money faster. You can also use
a player's progress to vary the difficulty of the game's challenges as she plays. This is
exactly the way Space Invaders works: The speed at which the aliens move in a given
wave is proportional to the number the player has already shot. The more the player
kills, the faster they move and the harder they become to kill. Their speed also
increases from wave to wave.

Games that measure progress in terms of travel through space have to rely on
careful placement and ordering of the game's challenges to create an appropriate
difficulty curve, and it will usually be the same every time the player plays the
game. Determining progress from the state of the game allows the mechanics to
adjust the difficulty automatically and to offer a different experience on each play-
through. You can also use the slow cycle design pattern to create oscillating degrees
of difficulty throughout the level.

proGress as a resource Vs. dynamic locks and keys

Treating progress as a resource is similar to, but more powerful than, using a dynamic
lock-and-key mechanism. With a lock-and-key mechanism, even a dynamic one, progress
toward unlocking that one lock is like optimizing a single resource. however, the way
that a lock-and-key mechanism affects the gameplay always depends on the mission
structure (when the player encounters the lock and what it unlocks) and its state is
binary—either the player has access to the goal or not. Treating progress as a resource
can have more subtle effects on the game and allow a wider range of effects than simple
wins or losses. For example, in a game in which the objective is to score a number of
points before the game ends, you can win by barely making that target or win by a large
margin. These differences are subtle but make progress as a resource more versatile.