Starcraft AI blog

Today is Steamhammer. With a mid-rank finish and the widest range of builds, plus informative game records, Steamhammer may give us the best insight into how other bots played.

The tournament was 100 rounds, and Steamhammer was configured to remember the previous 100 game records, because in play there is no reason to remember more (earlier records are increasingly discounted). Steamhammer also had pre-learned game records for many opponents, so when the game record count reached 100, new records added caused old pre-learned records to drop away. Not all 100 tournament games happened for each opponent, but the pre-learned games filled in the small gaps so that Steamhammer ended up with exactly 100 game records per opponent in every case.

The “opening” table counts Steamhammer’s opening choices. The “plan” table shows the plan that Steamhammer first predicted that the opponent would play, then recognized that the opponent was playing. Both prediction and recognition can be wrong. The timing table is new this year, an attempt to get a little more information out of Steamhammer’s rich game records. For some events, it gives the count of games in which the event occurred, and the median time, earliest time, and latest time it occurred in those games when it did. The times are given under the assumption that 1 second of game time is exactly 24 frames, a simplification.

• gas steal attempt - When Steamhammer sent out the drone to steal gas (if it did).
• gas steal success - Whether the gas steal attempt succeeded in taking the opponent’s gas. Steamhammer doesn’t record the time it happens, so this is only a success count.
• enemy scout - When the enemy scout first reached Streamhammer’s base.
• enemy combat units - When the first enemy combat unit was seen.
• enemy air units - When the enemy is first known to have tech for flying units (except overlords).
• enemy cloaked units - When the enemy is first known to have tech for cloaked units.

It looks like Locutus opened forge-expand every game. It worked. Steamhammer desperately tried everything, including ZvZ builds and island builds, and finally squeezed 3 wins with a risky extreme macro opening, 4 hatcheries before spawning pool, which was able to win one game in five. I should add 5 and 6 hatch before pool and see if they help.

Locutus rarely made corsairs or dark templar. I wonder what its criteria are? Maybe it won before it got that far. The scout was usually quite early, and the first combat unit was seen late, as expected for a cannon-first opener.

I played over the 3 wins. They were in rounds 65, 70, and 73; after that, I expect that Locutus found a way to win. In 2 games, Steamhammer pulled ahead in early economy with its greedy opening, then struggled to defend and fell into a losing position. But Locutus got most of its units stuck in its base, and Steamhammer was able to turn it around and win after a hard fight with critical defiler support. In the third win, Locutus chose a zealot-archon unit mix that Steamhammer knows how to cope with, and zerg powered through.

PurpleWave in contrast went with mostly 2 gate openings against Steamhammer; that’s what “heavy rush” means for protoss. Steamhammer countered with early sunkens plus hydras or, less successfully, mutalisks (this version had a bug that weakened mutalisk play). There are also 3 wins with a ZvZ fast mutalisk opening. 2 gates should beat that, so protoss either played poorly or chose a different build in those games.

BananaBrain contrasts with both previous opponents in that it played a variety of builds. Steamhammer was unable to predict what was coming. It looks strange that the best reaction was an opening designed to counter terran factory-first builds that include a vulture runby, but in fact it is a mildly specialized 2 hatch mutalisk variant and not so surprising. BananaBrain made corsairs and dark templar in most games.

DaQin played forge-expand and has similar timings to Locutus, for the same reasons. The fast scout is to allow adjustment of the cannon count and timing, and the late combat units are due to getting a gateway later. Steamhammer couldn’t find any better reaction than to try to bust with zerglings, either early or late, and it was not particularly successful.

ZZZKBot mostly played a turtle-into-mutalisks strategy against Steamhammer, and was somewhat successful. You can read the idea straight out of the tables above. The 2:25 earliest timing but 4:06 median timing for combat units says that ZZZKBot sometimes rushed zerglings, but usually not.

Microwave played a 9 pool speed build into expansion and then spire, which you cannot read out of the plan table because Steamhammer didn’t recognize it accurately. But in the timing table you can see that combat units (zerglings) were early and air units (mutalisks) were not late.

Steamhammer was not able to steal Microwave’s gas. It probably should have stopped trying.

Look at that huge range of scout timings! 0:34 means that the scout SCV was sent immediately at the start of the game and went directly to the zerg base. 15:09 probably means that no enemy unit got into the base until the end of the game when Steamhammer lost (Steamhammer is on BWAPI 4.1.2 and cannot detect scans). Steamhammer prevented the scout entirely in 13 out of the 100 games by its own count; 15:09 is probably the same. Steamhammer was not able to steal Iron’s gas, and did eventually give up trying.

Steamhammer liked 7 pool against XiaoYi, just as Microwave did, but also liked its dawn hydra rush.

Thanks to pre-learning, I expected Steamhammer to play its overpool turtle build every game. I’m not sure why it didn’t. I also don’t know how it hit on the 5 scout build, which means send out a drone at 5 supply to scout very early, then leave all decisions to the strategy boss. It’s a logical try against a random opponent, especially one that has a single strategy for each race, and it was fairly successful. But it did not appear in the pre-learned data.

AITP scored zip against both mass zerglings (9HatchExpo9Pool9Gas) and against fast mutalisks (AntiFact_13Pool). And it successfully scouted Steamhammer’s base only 25% of the time. If you don’t scout reliably, it will be hard to withstand rushes.

Steamhammer was not able to judge whether BunkerBoxeR was playing a proxy (with its proxy bunker) or a worker rush (since it sent SCVs in support). But it didn’t matter. The reactions are nearly the same. Since BunkerBoxeR never wants gas, stealing its gas was a waste.

Steamhammer knows 142 different openings. In the whole tournament, it was only able to try 111 of them! It tried the most openings versus protoss, since it was looking everywhere for an escape from the overwhelming top protoss bots. Most openings were tried only a few times and lost every game, which means that Steamhammer would have performed better without them. That’s expected and even intentional; my plan is to add smarts until it is able to make good guesses about what to try. The work is underway.