Thursday, February 28, 2008

Economies - Part 1: StarCraft

My experiences as a competitive player, at least as a successful one, comes from the realm of RTS. My successful competitive career started with Blizzard's Warcraft III: The Frozen Throne. I've competitively played many other "conventional" RTS games such as StarCraft, Command & Conquer 3, Rise of Nations, World in Conflict, and others with varied yet respectable levels of success. The point of this post will be to illustrate the different ways that resources are collected and spent affect the pacing and balance of competitive RTS games.

First, we start with StarCraft. Its economy is pretty simple: You collect Minerals, your main resource, from Mineral patches. Its rate of assumption is more or less capped, but requires a large number of workers to optimize the field, so a player's income grows over time, and as economies grow expansions are needed to continue to provide the required money. The game's second resource, Vespene Gas, is very much capped. Efficient harvesting only requires 3 workers as opposed to roughly 25 and similarly, expansions are required to broaden its harvest.

With the introduction out of the way, we move to their importance. Literally every single unit in the game requires Minerals for production. Most low-tier units (workers included) require only Minerals, while high-tier units require increasingly larger Gas sums for their production. It quickly becomes impossible to produce solely high-tier units without uselessly accumulating a large bankroll of Minerals. As opposed to simply banking an otherwise useless resource, good players will simply produce droves of their low- and mid-tier units.

In some match-ups, such as Protoss vs Terran, these low tier units are optimal, allowing the player to spend his Gas to "tech," to reach higher tiers without slowing unit production noticeably. Thus Protoss are able to research upgrades and produce high-tier units to supplement their standard armies without succumbing to an extended tier-two push (more on this in another article). This insurance that the player is able to tech while attempting to defend and attack faithfully lets the match-up evolve as the game ticks on. The game will never stagnate at two units vs two units ad nauseum. Now the limit on Gas requires the player to make choices: Do I want this vital upgrade for my Zealots? Do I want air units faster? Do I need more Dragoons, even though it will slow my tech? Which of my three tech trees (Robotics, Templar, Air) do I want to use?

Utilizing a limited secondary resource has a number of practical uses in game design. In RTS games, there are often many units that are hard to counter: units that require specific strategies or units to defeat. If we are to continue to look at StarCraft, examples are invisible attackers like Dark Templar and Lurkers, air attackers like Mutalisks. These units all appear slightly past tier 2, in what I like to call Tier 2.5: After reaching tier 2, players must make a specific building or complete a specific research to allow their production: Templar Archives for Dark Templar, Lurker Aspect for Lurkers, and a Spire for Mutalisks. Note that these units have a variety of methods to ensure that they cannot be rushed to, but prominently, each unit costs at least 100 Gas, a fairly steep investment.
  1. A player cannot quickly tech to the highest units as he must accumulate enough Gas over time to enable those options. This allows designers to force certain units to only appear after a certain amount of time. Hard-to-counter units like heavy air or invisible attackers are a bane on the unprepared. Forcing them to only appear after ten minutes allows designers to balance its appearance mid-game with its appearance late-game without worrying about an early-game influence.
  2. A player must choose between his best options. Limiting the vital second resource makes players choose between mid-tier macro, upgrades, or tech for high-tier units. And as we all know, interesting choices make for interesting games.
  3. A player must continue to create his low-tier units, as well as allowing designers to optimize the effectiveness of upgrades and high-tier units. Making high-tier units extremely effective is an efficient and attractive option: Players should always have an incentive for climbing the tech tree. However, because their availability is limited, players need other ways to spend their Minerals while their Gas is taxed. The most attractive option in this case is often to create their low- or no-Gas units such as Zerglings, Vultures, Zealots, and Marines. In some cases they are used simply as tanking or scouting units, while in other situations they are the core of a player's army, supplemented by the higher tier units.
Designers can achieve many of these results through other means in other economic systems:
  • They can hard-cap the number available a unit, "You may only have one Mothership, Ion Cannon, etc." However this cap does not present players with a real choice. It is most likely capped because it's extremely powerful and should always be created.
  • They can affect the cost of a unit, however this presents a problem in that players simply choose between their low-tier and high-tier options. Certainly, roles come into play (Anti-air, tanking, damage output, range), but for similarly-themed units, it is difficult to truly balance the effectiveness of two similarly-themed units if players freely choose between the two without making them too similar.
  • They can affect the build time of the higher-tier units to amounts higher than would otherwise be optimal, which forces players to either spend huge resources on additional production buildings or to spend the structures not building their high-tier units to build their lower-tier units. This has a mix of problems between the two aforementioned "solutions" in that they are either completely worth building the additional structures to produce optimally or they may be entirely ignored. In some cases this system can work out very well and while the units are effective, investing in additional production buildings may be problematic. This is more tactfully done with the finite second resource, when a player wants to produce this unit later in the game, it is more easily acquired while having the same early-game effects.
While this begins to touch into unit design itself, it is important to remember that low-tier and high-tier units should all have uses. Maybe they aren't useful in every match-up all the time (Marines, Firebats, and Medics vs Protoss, Carriers vs Zerg, etc), but there should be a decided set of uses for each unit, and while high-tier units may do some of these better, they should not have absolute superiority. Ultimately, while high-tier units are often more effective in many scenarios, they cannot be acquired right away, and uses are still found for low-tiered units.

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