Starcraft AI blog

Steamhammer versus BananaBrain on Moon Glaive was a fun back-and-forth game. Well, it was Randomhammer as zerg, that’s Steamhammer.

Steamhammer opened with a fast hatchery before pool, preparing zergling aggression. BananaBrain was also aggressive; it hid 2 gateways on the left of the map where they were unlikely to be scouted early. The gateways were more or less midway by ground between the 2 bases where zerg might be.

The zerglings outfought the zealots, then made a beeline for the protoss base, where they wrecked the economy. Protoss was left with 1 probe mining and 1 more in production.

But protoss had still been producing army during the attack, though the units were too far away to defend the main. It’s the drawback of a proxy opening: Close to the enemy means far from home. Steamhammer did not see the units and concluded that it was safe, so it started a third base (see 8 o’clock in the minimap), added a hydralisk den, and morphed a lair in its natural. A good human player would have predicted the protoss army size and been ready for it, but bots to date are weak at inference. Steamhammer could not save the lair in its natural and threw away units trying, then pulled together a defense in its main barely in time. BananaBrain ran by the sunkens to attack drones, one of its great skills, and it was zerg’s turn to fall behind in economy. Notice how much the protoss probe count has recovered. The zerg drone count fell to 5 shortly after the picture.

Three drones escaped the carnage and ran across the map to the hidden zerg third, which protoss did not yet know about (though a human player would have guessed its general location from the direction of arriving units). After a short distraction when a small zerg squad again attacked the protoss main, BananaBrain put heavy pressure on the defended zerg main. Both sides were racing to rebuild workers and trying to afford tech.

It was around here when BananaBrain repeatedly tried to expand, and Steamhammer’s patrolling Recon squad repeatedly denied it with only a few units. Protoss chose to keep attacking rather than defend an expansion. BananaBrain has added tech and sent out corsairs, and zerg protected its overlords with a spore colony in the main. Steamhammer’s mineral bank of 900 is a sign that it is short of hatcheries—it knows that, and wants to add hatcheries.

Needing more hatcheries, Steamhammer also tried to expand, in a rather strange pattern where the first hatchery at a new base was offset and the second one placed at the base location. The natural was denied, then a new base at 10 o’clock was about to be killed by zealots—when a scouting observer finally ran down the left of the map and discovered the hidden base, now bustling with drones. The protoss army suddenly had a more alluring target, and ran there to raze it.

But Steamhammer had mined its third base for most of the game, and BananaBrain had never been able to expand. The protoss main was dry, and the zerg 10 o’clock now had a half dozen drones at work, and it shows in the production tab. Steamhammer scourged the sky of corsairs, defeated the zealots with hydra-ling and a few mutalisks, and tore down the proxy gates before finally tackling the protoss main.

Whew, no big fights because of the damaged economies, but an exhausting struggle. Either side could have won easily at various points with smarter play at that moment.

New bot Crona is, as it says in its description, BananaBrain playing zerg. It was uploaded today and has started out well. The name “Crona” is after an anime villain.

Sp far, I have only seen Crona play with zerglings and mutalisks, no other units. Here are the names of Crona’s openings, extracted from the binary. “Main Muta/Hydra/Ling” looks like an unrelated string that sneaked into the list, but maybe it’s an opening too.

ZvZ_2hatchling
ZvZ_5pool
ZvT_2hatchling
ZvT_4pool
ZvT_2hatchmuta_12pool
ZvT_2hatchmuta_12hatch
ZvP_2hatchling
ZvP_5pool
ZvP_4pool
ZvP_2hatchmuta
Main Muta/Hydra/Ling
ZvU_2hatchling

The build ZvZ_2hatchling is the “Styx build” of 9 pool, 3 pairs of zerglings, second hatchery, extractor, research zergling speed and produce zerglings for a long, long time. (Note 1: One of the rules of naming is that the origin of a thing cannot be the name; you have to pick something later. Note 2: I’ve tested both variants, and I’m pretty sure that the PurpleSwarm variant with extractor before the second hatchery is better.) Likely the other 2hatchling openings are too.

When playing 4 pool, and presumably other builds, Crona sticks with 1 hatchery and 3 drones for a while, then transitions to 2 hatcheries and 7 drones, then later to 3 hatcheries. I assume the sequence continues. My impression is that the expansions are on a timer: I’ve done this long enough, time for another hatchery. It’s a simple way to slowly increase pressure on the opponent.

Crona’s zerg play is good—see its results—but still looks a little rough to me. It doesn’t scout with its overlord. It has a glitch where, at a certain point in the opening, all the drones move away from the minerals for a second before returning. Crona seems a little confused about drone transfers in general. These things should not be hard to fix, though.

I see terran openings in the binary too. Can anybody guess what the terran BananaBrain will be called?

I wrote a script to analyze BananaBrain’s game history files, which record its experience with each opponent. For now, I had the script summarize the strategies played and the enemy strategies recognized. The history files also record the map and a value that represents the game duration. History files are rich with information, and there are many ways to summarize it. It would be interesting to see how strategy usage and win rate vary by map, among other possibilities.

The same script should work with minor changes to summarize Microwave’s history files.

BananaBrain had prepared history files for the opponents #1 Locutus, #2 PurpleWave, #5 Steamhammer, #6 ZZZKBot, #7 Microwave, and #8 Iron. Data from the prepared history files was not copied into the write directory. That is different from how Steamhammer and Locutus keep their game records, and it has the nice effect that the tables show exactly what happened in the tournament, from BananaBrain’s point of view.

For each opponent, the left table is BananaBrain’s choice. The right table is BananaBrain’s idea of what the opponent did. All the win rates are from BananaBrain’s point of view, so that, for example, when Locutus played P_1gatecore, BananaBrain won 5% of the time. Of course, the opponent’s view of its own strategy is likely to be more fine-grained than BananaBrain’s. To take the extreme case, Steamhammer played 30 different openings against BananaBrain, and BananaBrain recognized them in 8 categories.

As you might expect against Locutus, the best choice was a fast expansion.

Is the single game of enemy P_fastexpand a misrecognition? I suspect that Locutus played otherwise, and BananaBrain didn’t see everything and wasn’t able to draw the right conclusion. Or maybe it’s a bug somewhere. PurpleWave and McRave also show a single P_fastexpand game.

Against PurpleWave, different zealot rushes worked best. Maybe it is because zealot rushes depend for their success more on execution than on the enemy’s strategic reaction. PurpleWave is particularly good at reacting to the enemy strategy, and BananaBrain is good at execution.

BananaBrain made quite a variety of tries, and was most successful with... zealot rush and dark templars, which are kind of different. BananaBrain’s varied opening choice is a strength.

2 gate zealot openings work well against Steamhammer—but only when played by PurpleWave or BananaBrain. Steamhammer can usually defend versus a lesser protoss.

I like that BananaBrain varies its opening choice even when several openings win 100%. (Steamhammer does too; if more than one opening has scored 100% so far, Steamhammer chooses randomly among them.) Playing a strong opening gives the opponent one problem to solve (“how do I survive this?”). Unpredictably playing one of several strong openings sets the opponent two problems (“what is this fiend doing, and then how do I live through it?”) which must both be solved, more than twice as difficult.

Bulldog! That involves protoss dropping zealots, typically on cliff tanks, with a simultaneous attack by ground. When successful, a bulldog can abruptly break a terran defense that is sound against any purely ground attack. I don’t think I’ve seen BananaBrain play that; I should watch more games versus terran. Can anybody point out an example?

The Stove worked against XiaoYi? Again, XiaoYi shows weakness against tricks. The Stove involves making scouts to harass while teching to dark templar. It should not be hard for a good terran to defend against; notice that Iron dealt with it well enough.

It looks like most openings performed similarly against McRave, and BananaBrain struggled to identify what worked. I imagine a fierce learning battle, both trying to keep one step ahead.

BananaBrain apparently does not have a bunker rush recognizer.