Starcraft AI blog

Steamhammer 2.4 is uploaded. Since I never got around to releasing the source of the previous version, I’ll release source shortly.

This version has 2 points of focus: First, fixing critical bugs that are responsible for many of the losses against weaker opponents, and second, coping with the deadly Styx opening. I wrote 18 new openings, 10 of which are connected to the Styx opening.

configuration

• Added the Config::Strategy::HumanOpponent flag for games against humans. It’s false by default, since almost all games are versus bots.

critical bugs

• Cancelling mutalisks just before making them is fixed. It happened intermittently in some openings. A spire takes 1800 frames to build, and Steamhammer is configured to conclude that production is jammed if there are 1440 frames without production. In some cases, the opening build might pause production for longer than the limit while saving up for mutalisks; a jam clears the queue and drops out of the opening, so the mutalisks were never made. I fixed it with a special case test, since only this one case was failing.

• Gas deadlock is an emergency that happens when Steamhammer needs gas for the next item, and has the extractors for it, but finds itself unable to collect the gas for some reason (for example, the base is under attack so the drones ran away). It clears the queue to try again. The condition for recognizing gas deadlock was too loose, and sometimes declared deadlock falsely. I tightened it up.

• Tracking of geysers and refinery buildings seemed to be wrong in some cases. I was not able to pin down any bad behavior it caused, but the code looked confused and I’ll be surprised if nothing is corrected.

• Combat sim is more fixed. In the previous version I fixed bugs in setting up the combat sim, related to short-circuit judgments when facing cloaked units. There was still a bug, and I traced it to... checking whether a unit’s air weapon was unequal to BWAPI::UnitTypes::None rather than BWAPI::WeaponTypes::None. Thank you C++ for your “helpful” type checking. This fix will make mutalisks more aggressive, as they should be, in certain situations.

macro

• Restored the setting of 2 workers per mineral patch for terran and protoss. It had been accidentally set to the zerg value of 1.6.

operations

• Against certain stronger enemy units, send more defenders. If an archon is in your base wreaking havoc, 2 marines will not stop it.

• The natural expansion cannot be one of the map’s starting bases. This fixes a problem that came up on the map Baekmagoji.

• StrategyBossZerg::enemySeemsToBeDead() works more nearly as intended. There was a minor bug. The enemy is considered to be dead and ready to be buried when all these conditions are met: 1. The enemy starting base has been found (so it can’t happen immediately when the game starts). 2. The enemy has no known surviving bases. 3. The known enemy ground army is not strong enough to threaten to win. 4. The enemy has no known anti-air units or anti-air static defense. When the enemy looks dead, Steamhammer techs to mutas and switches to a unit mix of drone + mutalisk. The mutalisks can efficiently hunt down any hidden or floating buildings.

unit control

• The micro system drops positional orders for which the position is “close enough” to the previous order. If code orders a move to (x, y) and then on a later frame a move to (x, y+1), the second order is dropped. The tolerance is a few pixels for short-range moves, larger for long moves. This reduces command spamming and smooths unit flow. In the long run, I ideally want to reduce Steamhammer’s APM to human levels.

• Targeting priority for enemy buildings is factored out and more nearly standardized across unit controllers. Streamhammer should destroy enemy bases a little more purposefully, with fewer cases of zerglings tearing down the spire while mutalisks tackle the spawning pool.

• Enemy observers are a higher priority target for ranged units and scourge, depending on the situation.

zerg

• When in book, if we have no zerglings, do not change a planned zergling into a drone. Steamhammer likes to skip zerglings when it foresees no danger. A similar change was already made for the case when it was out of the opening.

• Queen bug: The queen believed it could infest an unfinished command center. “It has few enough HP, let me fly across the map and take it.” When the building SCV was killed, the queen might sit over the unfinished command center forever. “This infestation sure is taking a long time. Oh well, stick with it!”

• Queen bug: When using broodling, the previous version was intended to be willing to make 2 queens, not the usual 1. After testing the feature, I introduced a typo that prevented it from working. Fixed.

• Prevent production freezes related to queen upgrades. Rare but painful.

• Allow air upgrades in any order, using 1 or 2 spires. Formerly, air carapace had to be first (or else production freezes were possible) and Steamhammer could upgrade in only 1 spire. This any-order-is-OK improvement was made earlier for ground upgrades.

openings

• ZvZ_Overgas8Pool fills a small gap in the repertoire. A very small gap.

• 973HydraBust is a precise modern build versus protoss forge expand. The name is because you are supposed to end up with 9 drones in your main, 7 in your natural, and 3 at a third base. Steamhammer does not have the skills to distribute the drones efficiently as intended, but it does get the right total count.

• 2HatchMutaForever covers a weakness in the zerg strategy boss: There are times when growing the mutalisk flock is best, but the strategy boss doesn’t understand the value of stacking air units and prefers to switch into a different unit mix. The opening doesn’t really make mutalisks indefinitely, only for a long time. It also gets air upgrades.

• 2HatchFakeHydra and 2HatchFakeMuta are deceptive openings that make both hydralisk den and spire. The fake hydra opening makes a hydralisk den when the enemy scout should see it, chases the scout away, and adds the spire later. The enemy may predict hydra play or lurkers. The fake muta opening is similar but in reverse.

• 5HatchPool makes 5 hatcheries before spawning pool, an extremely greedy opening for use against opponents that move out late. (See my mention of Locutus in what Steamhammer learned. I’ve seen 6 hatch before pool work against a bot.) ZvP_5HatchPoolHydra is a specialized version that follows up with mass hydralisks. 5HatchPoolLing gets an evolution chamber before the spawning pool, so that when the first zerglings hatch, melee attack +1 is already half finished. The flood of lings is late but massive.

• The powerful Styx build. The openings 9PoolHatchSpeed7Drone, 9PoolHatchSpeed7DroneB, 9PoolHatchSpeed, 9PoolHatchSpeedAllIn, 9PoolHatchSpeedAllInB are variations on the Styx build of 9 pool, 3 pairs of zerglings, hatchery, extractor (leaving yourself with 7 drones), zergling speed, and deluge the enemy with zerglings (7 drones are enough). That exact build is 9PoolHatchSpeed7DroneB. The versions without a B have the extractor before the second hatchery, which gets faster zergling speed and a slightly slower hatchery. The versions without 7Drone use the extractor trick to end up with an 8th drone without losing time. The 8th drone does not make the zergling attack stronger, because 7 drones are enough to keep the 2 hatcheries completely busy producing, but it does establish leeway to lose a drone to accidents, make an emergency sunken, or transition into another plan. The plain version 9PoolHatchSpeed makes fewer zerglings and leaves the followup to the strategy boss, which is not too helpful because the strategy boss doesn’t understand the idea.

• Anti-Styx openings. If you know your opponent’s exact build order, you can always choose your own build to gain an advantage. (Don’t be predictable!) If the opponent is too greedy, you can clobber them with a rush or a bust before they’re ready. The Styx opening is not greedy; 9 pool is what you play to be safe against cheese. When the opponent is not greedy, you gain an advantage by being greedier, to a calculated extent. AntiStyx_9Pool is the simplest try. It uses the extractor trick for the 8th drone, and turns the drone into a sunken. The zergling wars are about equal, but the sunken at home is safer and allows more freedom of action because there is less need to hang back in defense. At Steamhammer’s level of play, the advantage is slight. However, this anti-Styx build is valuable as a general-purpose anti-cheese build; I configured it for that too. AntiStyx_3Hatch and AntiStyx_Muta are more successful at defending against the Styx opening. They open with overpool rather than 9 pool, gaining a lead in drones. Both make 1 sunken and use the safety it provides to scrape out more drones. The 3 hatch followup adds a third hatchery to eventually win the zergling wars, while the muta followup techs instead. The safe path is narrow; I’m curious to see how well the openings perform in practice.

Turtle openings can also cross the river Styx. Some turtles swim well, and they do not have the same weakness as Achilles. See wins over StyxZ by ZurZurZur, by Simplicity, and by Microwave with its turtle build.

• 9PoolHatchSpeedSpire and 9PoolHatchSpeedLurker are my try to pre-empt bot authors who may add a recognizer for the dangerous Styx opening so they can counter it. These builds start out with the Styx opening stem but transition into tech.

• I made tweaks to AntiZeal_12Hatch and 12HatchTurtle. They should be a trifle stronger.