Game Development Reference
In-Depth Information
Upgrades and Technology Trees
In a game with a limited number of unit types, the players can sometimes exhaust
the interesting battle combinations too quickly. For example, the knights, archers,
and barbarians of
The Ancient Art of War
aren't enough to hold players' attention
over many campaigns. You can make a game more interesting by adding more unit
types, but if all the unit types are available at the beginning of a game, the player will
undoubtedly concentrate on the most powerful ones and ignore the weaker ones.
To resolve this problem, you should look for a way to introduce new units or to
upgrade the existing ones as the game progresses. These upgrades can improve the
values of units' attributes or give the units entirely new capabilities. An upgrade
might occur as a reward for some achievement. In checkers, for example, moving a
piece to the opposite side of the board turns that piece from an ordinary unit that
can only move forward into a king that can move both forward and backward.
Because it takes a while to reach the opposite side of the board, kings don't appear
until well into the game.
RESEARCHING UPGRADES
Checkers is an abstract game with an arbitrary rule for upgrading units. In more
representational games, the unit upgrade process is often characterized as a form of
research that the player must initiate; it takes a certain amount of time and perhaps
the expenditure of some resources. If your game offers several different upgrades,
you may wish to organize them into a sequence, such that some upgrades become
available only after others have been achieved. You may also offer the player a
choice of upgrades to research at any given time, which gives her an interesting
decision to make: Which is the most advantageous upgrade to choose given the
units she has available and her preferred style of play? (A player who prefers a
defensive style, for example, may wish to choose upgrades that enhance the defen-
sive rather than the offensive capabilities of her units.)
SINGLE-UNIT, UNIT TYPE, AND GLOBAL UPGRADES
You may create a number of different t y pes of upgrades: those that apply to a single
unit (such as the conversion of a piece to a king, as in checkers); those that modify
the capabilities of all units of a given type (such as the siege tank upgrade in
StarCraft
,
which gives all tanks the ability to operate in siege-tank mode once the upgrade
has been researched); and those that modify the core mechanics globally (such as
the Hoover Dam invention in
Civilization
, which improves its entire society's pro-
ductivity and reduces pollution). In role-playing games, skill upgrades naturally
apply only to the individual character that has learned the skill, but in strategy
games it is more common to apply a unit type upgrade to all the player's units of
that type simultaneously. That makes the process of retrofitting the existing units
unnecessary, so the player doesn't have to think about it. If you're making a highly
representational war game, however, you may want to require the existing units to
