Starcraft AI blog

In the Undermind 42 podcast, purple Dan Gant offers the opinion that the bot metagame and human meta will be similar in the long run: “there may be some differences but those differences will be slight” as bot and human meta converge over time.

Maybe so. We won’t know till we know. There are reasons to be sceptical, known instances where bot and human meta differ for reasons that seem fundamental and likely to endure. Here are examples. It’s possible to argue about each one, whether it constitutes a serious or a minor meta difference, but there certainly are differences.

My examples are all in zerg matchups. That might be because zerg is affected more, or just because I know more about zerg. I suspect the latter.

Locutus-style dragoon micro

Cadenzie had the impression that once Locutus had enough dragoons, hydras became weak against them. A dragoon has high speed and a longer range than a hydra, so with perfect micro it makes sense. We’ve seen similar events in other Locutus-human zerg games: Zerg has to win by playing a more efficient build order to stay ahead in macro—but in the limit as bots improve, protoss will have efficient reactive builds. If this is true, then zerg has to seek another way to fight dragoons.

I suspect that the answer is to include speed zerglings in the unit mix along with either hydras or mutalisks. We’ve seen games where tscmoo zerg can coordinate its lings and mutas to beat Locutus dragoons at low cost: The lings get in among the goons, interfering with their movement, and the combined arms attack becomes very effective. A similar tactic should work with lings and hydras, but it would require tactical coordination and strong micro.

In any case, higher efficiency of dragoons in bot play seems like a fundamental meta difference. Wraiths are another unit with high speed and long range, and they also show higher efficiency in bot play (among the best terrans).

splitting irradiated mutalisks

In pro ZvT, irradiate counters mutalisks. Once terran has irradiate, it rarely makes sense to spawn any more mutalisks. That is because mutalisks are stacked tightly to attack, and when 1 mutalisk in the stack is irradiated, the UI provides no way for the zerg player to select it out. You have to separate the mutas until you find the glowing one. Even the greatest zergs can’t quickly and reliably separate the mutas to split out the irradiated one, so frequently all the mutas take serious damage.

In bot games, the irradiated muta can instantly fly away from the group. Irradiate becomes a weak counter to mutalisks, and zerg may well want to continue spawning mutas. Terran will have to seek another counter.

This meta difference can be chalked up to a design issue with BWAPI. BWAPI provides bots the ability to know the status of every unit in a stack, and to be able to pick out any one of them, while the game UI for human players does not. It’s not obvious how to revise the API, but we may want to do it at some point.

mass unit control

Occasionally a top human zerg will collect more than 12 mutalisks—more than one control group—and harass with them all. It’s mechanically difficult, because each control group has to be separately commanded. Jaedong was the first to demonstrate the skill, as far as I have seen. Only the best zerg players can do it well.

Bots, of course, can control units individually and don’t much care how many there are. Bots can, in principle, better control large armies, such as large mutalisk clouds. I’m not sure how important the effect is, but it seems that it ought to have some affect on the meta.

Also see Artosis’s comment about his McRave game, “I’ve played against and cast the best Protoss players in the world, and this bot had a way better economy than anything I’ve ever seen.” Underneath, it is the same issue: Bots can individually control units, so they can make every worker at the earliest possible moment, never leave it idle, and on top of that do micro tricks to speed up mining for the entire game (humans can do that in the very early game). A potentially stronger economy is a fundamental meta difference.

Also Cadenzie’s comment “the individual unit control and multi-tasking is sometimes beyond human ability.” A difference like that must have metagame effects.