Strategy Games - Fundamentals of Game Design - page 438

come back to headquarters to fit them with their new gun, engine, radio, or what-
ever other feature it is that the player has researched.
PERMANENT AND TEMPORARY UPGRADES
In turn-based games with long, complex campaigns (such as Civilization or X-COM ),
designers often spread the upgrades out over time, spanning several levels. Each
time an upgrade is achieved, it lasts for the rest of the game. These permanent
upgrades strongly support the player's sense of progression through an extended
game. They typically occur only infrequently and represent a major achievement
when accomplished. Permanent upgrades are ideal for game-time periods that span
months or years.
In RTS games, however, you may want to have the research and upgrade process
work fast enough to produce big changes in the gameplay within a single level but
not fast enough to carry over to the next level. These are called temporary upgrades .
This puts more pressure on the player, who has to decide quickly whether to
expend resources on research or on building new units to help fight a battle taking
place in real time. Dungeon Keeper is a good example of this kind of game: In each
level, the player's creatures research a set of magic spells while still defending their
dungeon against invaders. With temporary upgrades, the player loses the benefit of
her research when she goes on to the next level; she has to research the technology
over again. This seems a bit peculiar, but it works well if you don't think of the lev-
els as part of a continuing story. It's more credible if you present each level as an
independent scenario, unrelated to the others—as Dungeon Keeper in fact does .
TECHNOLOGY TREES
If your game has a large number of upgrades, you should organize them into a
branching tree structure, in which achieving one upgrade makes available a choice
of several others that are logically related to the preceding one. See Figure 14.3 for
an example. Achieving the steam engine, for instance, could give the player the
opportunity to research the railroad, steamships, or powered factories. Strategy
games usually characterize these advancements as technological research, so such a
structure is called a tech tree even though some of the upgrades may not actually be
technological. In role-playing games, a similar mechanism applies to upgrading a
character's individual skills; in that context it is called a skill tree , but the function
is the same: It is a diagram of the available upgrade paths for a unit.
Once the player chooses to research an upgrade on a particular branch, you can
force her to complete all the upgrades that are part of that branch before moving to
another branch or prevent her from ever researching upgrades on another branch.
So, for example, choosing to research agriculture might force the player to stick
with agricultural advancements, and other upgrades such as fishing or animal hus-
bandry would be closed to her—either until the agricultural branch has been
completed or perhaps forever. This restriction encourages asymmetric play; if one