Starcraft AI blog

The game Steamhammer-Bereaver is a good example of Steamhammer’s defiler skills, both the good and bad points. Steamhammer gained an early advantage and contained Bereaver to its main, so the outcome of the game was not in doubt, hive tech or not. Bereaver mounted a strong defense at its ramp and held on for a long time. A timid zerg might have feared to attack and lost on points when the game time ran out—but of course Steamhammer is not timid.

The defiler dithered for a long time. Consume research finished at about 15:45 into the game, and the defiler filled up on energy within 15 seconds after, so that part was OK. A first attempt to break up the ramp was repelled with storm; the defiler was too far back and unable to help, due to lacking squad coordination. The second attempt to break up the ramp was at 18:20, and this time the defiler was in range. That’s about 2 and a half minutes from when the defiler was ready to act until it finally did; it had plenty of time in between to swarm or plague. It would have been worth it to sacrifice the defiler to plague the defenders.

Excellent swarm placement! The defiler had energy to cast a second swarm farther into the enemy base, but did not. Even so, the one swarm nullified the dragoons and cannons and ensured that the attack would succeed if pressed. Thanks to my modifications, FAP understood that it would succeed and Steamhammer did press until it broke through. The attack had to be under way before the defiler could support it; Steamhammer has no ability to swarm (or plan to swarm) in advance of an attack. Steamhammer attacks when maxed, so in most winning games an eventual attack is guaranteed. When the swarm does come, it is generally well-positioned for where the units are at the moment, rather than where they are going or where they want to be.

The defiler seemed to get confused and did not contribute again until the very end, when it laid down a perfectly-placed plague over a few protoss buildings that were about to be destroyed anyway. The laser-precise plague hit as many protoss buildings as possible while missing zerg units. It’s impressive in a way, and it may even have shortened the game... by a fraction of a second.

Still next: Base defense.

Curious fact: Steamhammer versions 1.1 and 1.1.1 are currently 3-0 versus Bereaver and 0-3 versus Killerbot by Marian Devecka. I don’t think it deserves either of those numbers.

The wins over Bereaver are exploiting a weakness. Early in the game, Bereaver techs too hard and doesn’t defend itself adequately, and some of Steamhammer’s openings mass-produce zerglings at a timing that exploits the weakness. I don’t expect all the openings to win; Steamhammer got lucky so far.

The losses to Killerbot are due to scouting wrong (in the most recent game) or taking poor tactical engagements (in the other two). Against Killerbot, these Steamhammer versions play a more solid counter to Killerbot’s overpool +1 opening. Steamhammer now goes overpool with an early second hatchery to outproduce Killerbot in zerglings for a while, occasionally winning outright but usually buying time to transition into spire, which Killerbot can’t defend. I think Steamhammer’s strategy advantage at least equals Killerbot’s skill advantage in tactics and crisis management. Steamhammer’s long term score versus Killerbot should be 50% or more.

You can’t tell how two bots fare against each other from a few games. You especially can’t tell how Steamhammer fares, because the bot plays so many different openings. I propose new wording for the law of small numbers: Small numbers speak small.

Here is the second half of the SCCAIT round of 8. Today I’ll go over the later 2 matches of the 4, from the second video.

Bereaver vs XIMP

The newcomer protoss Bereaver versus the old school carrier bot XIMP.

XIMP always cannons itself in and goes carriers. The strategy seems easy to counter, and yet somehow it is not so easy; XIMP is still highly successful. I think protoss has the most difficult time countering the carriers. Terran can make tanks and blast down the cannon wall, and zerg can stop the carriers and prevent all expansions with hydralisks. Protoss has counters too, but they are not as simple to execute.

In game 1, Bereaver opened with two gates. On seeing the cannons it had the sense to immediately start its own natural and soon take its 3rd as well, pulling ahead in economy. Bereaver added some scattered cannons of its own, which seems strange and inefficient to me, but also got templar tech and started storm research, which is good play.

When the carriers arrived, high templar apparently did not yet have storm energy. Bereaver caught XIMP’s third starting and stopped it, which was necessary, but had made too many zealots and cannons and not enough dragoons, which was not promising against carriers. If Bereaver had mineral excess and gas shortage, then it probably should have taken a 4th base sooner.

But Bereaver did get a 4th soon enough, built more goons, and with help from some poor tactical decisions by XIMP, defeated the carriers using dragoons and storm. Bereaver had held off the carriers and stopped expansions, so it won.

Game 2 followed a similar course, but XIMP’s carriers took the long way around the map and XIMP successfully started a 3rd base (on its second attempt), while Bereaver saw nothing and opted to attack the cannon wall, setting itself back. Bereaver ignored the 3rd too long and XIMP got cannons up there, while Bereaver didn’t spend its extra money on a new 4th base after losing its first attempt to the carriers. Bereaver’s game plan failed and XIMP won.

I noticed movement on the minimap which looked like a failed reaver drop in XIMP’s main, but we didn’t get to see it in the video.

In Game 3 Bereaver got confused by the map, Heartbreak Ridge: It sent a probe to take a 3rd but was unable to navigate the mineral block. The probe wandered aimlessly. “This way! No, it’s closed off. This way! No. This way!” Bereaver went down without much fight.

XIMP, by the way, understands mineral blocks and is able to mine them out. A bot has to do a lot right to play well, and XIMP does a lot right. Bereaver is strong but doesn’t quite have the same robustness.

Krasi0 vs Tscmoo protoss

Krasi0’s game plan is to expand and build up while holding off any attacks with efficient terran defense, then move out with a large force that is difficult for any enemy to oppose directly. Tscmoo protoss is unpredictable, but it has played many games lately with ceaseless pinprick harassment. The clash of styles between two top bots promises to be fun!

Game 1. Tscmoo opened with scouts, expensive units with powerful air attack and puny ground attack. On the one hand, objectively scouts are poor at harassment. On the other hand, opponents have proven weak against widespread harassment and protoss has few other options for it. Tscmoo has won games this way, including against Krasi0.

As the game went, the scouts stopped mining at Krasi0’s natural for too long; air defense took a while to kick in. Tscmoo quickly went up to 5 bases with a fleet beacon to upgrade the scouts and shuttles with reavers to add firepower to the harassment. Krasi0 was satisfied with 3 bases for the time being, which seems fine to me.

Well, Krasi0 built many turrets and had good enough positioning, and Tscmoo’s harassment achieved nothing. Krasi0’s first push won outright. Oh well.

Game 2. This time Tscmoo went dark templar. Krasi0 the strong defender was of course prepared, and the dark templar never got close.

Tscmoo followed up with arbiters and researched recall. Arbiters started flitting irregularly across the map looking for openings, but Krasi0 had again built many turrets in its main and there were few openings to find. An arbiter finally recalled the 3rd. It stopped mining for a time but was not fully successful because the zealots in the recall did not feel like giving their lives for Aiur. Units with no escape route need the all-in mentality: “Die I must. Let me sell my life dearly.”

Krasi0 pushed out and started taking down bases, and Tscmoo never made a strong move to defend itself. Arbiters flew around stasising random units but not firing. Krasi0 built an absurd number of turrets but was too far ahead to suffer from the needless expense. Tscmoo's play was not focussed enough to make progress; it came across as scattershot and ineffective. Of course, that is largely because Krasi0 defended with cautious thoroughness.

Next I’ll cover the round of 4, likely tomorrow on the same day that the finals are broadcast. I didn’t catch up with real time after all.

If you’ve been following SSCAIT games between the top bots, you’ll have noticed one striking change: 2015 Killerbot lost most games to recent versions of Bereaver, but the new 2016 Killerbot has just won 4 in a row.

The 4 games followed similar paths.

• Bereaver optimistically puts on some early pressure that Killerbot is more than ready for. Here is Killerbot’s simcity at its natural—it’s nothing you can attack with a few zealots.

• Bereaver sends out 1 initial corsair. Killerbot defends with hydras. Throughout the game, Bereaver usually keeps 1 or 2 corsairs in the air and gets some overlord kills but repeatedly loses corsairs to hydras.

• Killerbot gets aggressive with its hydralisk force, mixing in some lings. Bereaver gets reavers, defends, then chips away at the zerg army.

• Bereaver builds up power and pushes the zerg ground army back, aiming for a heavy attack. The wolf is at the door:

• Killerbot presumably notices the shortage of anti-air and goes mutalisks, the classic zerg counter to reavers. The wolfsbane is also at the door.

Bereaver can’t recover after the sudden zerg tech switch.

Both bots show risky over-aggression at times. Killerbot has improved its overlord protection and Bereaver’s corsair control—which used to be effective—is no longer alert enough to keep its corsairs alive. But that’s small beans; Bereaver’s strategic mistake is to rely on reavers without enough air defense to protect them. Corsairs are standard nowadays, but dragoon-reaver is also a classic unit mix.

As Igor Dimitrijevic said, Killerbot’s adaptation skills have become dangerous.

These 2 pictures are from a game between Bereaver and the AIIDE 2016 version of LetaBot. It was a great game—Bereaver lost its natural and narrowly held its main over and over against LetaBot’s powerful attacks, until finally LetaBot ran out of steam and lost. LetaBot didn’t scout Bereaver’s third base. But I want to pick out a funny detail:

I dub this reaver The Little Tailor.

Seven at one blow! One marine lived and kept shooting until the next scarab got it. It’s good reaver targeting.

Bereaver was reuploaded today, and apparently the new version introduces bugs because its play is worse in obvious ways. Until today Bereaver had been holding the #1 rank with seeming ease. I expect the problems will be ironed out before SSCAIT closes submissions for the tourney!

Even without bugs, Bereaver’s play is curious because it is a top bot, yet some of its weaknesses look simple to fix. Usually the weaknesses of top bots look difficult or time-consuming or at least troublesome to correct. I’ll give a couple examples.

1. Bereaver gets the reaver capacity upgrade, so that a reaver can hold 10 scarabs. Bereaver eventually makes a lot of reavers, so an upgrade makes sense—but the capacity upgrade? The way I see it, the main purpose of the capacity upgrade is to make reavers usable when your hands are too slow. Expert players don’t even use up the normal capacity of 5 scarabs, at least not until later in the game when micro becomes more demanding. It’s normal to send a reaver into the fight with 3 or even 2 scarabs in the magazine, because every scarab is a sunk cost and you never know when the reaver will die. Bereaver invests 200/200 for the upgrade and then builds 5 extra scarabs for 75 minerals more per reaver, and I don’t think it earns any return.

I imagine it would be a 1-line change to order the reaver damage upgrade instead. Instead of more expensive, the reavers would become more lethal.

2. Bereaver makes corsairs against terran, apparently to counter science vessels or dropships. There are times when it could make sense, but mainly on island maps. I have never seen Bereaver’s corsairs pay off in a game against a terran.

Again, it seems like a 1-line change to skip corsairs. It would be a different story if the corsairs used disruption web, but that’s for later in the game and it’s not half as simple.

Here are a couple of updates on top bots before I return to Overkill’s reinforcement learning.

Iron

For a while now, Iron has been playing a different strategy against protoss, going 2 barracks plus academy and attacking early with marines and medics rather than its traditional vultures. I’m a bit slow, but I finally realized why: It was having trouble against dragoons. Dragoons, adding observers in time to detect mines, are a strategically sound counter to Iron’s early vulture play, where tanks come late. Bereaver was handing Iron a string of losses with dragoon play. Time to switch it up!

Bereaver poked with 2 zealots but was unable to land a single hit against accurate micro.

Bereaver expanded early. I thought its force of 4 dragoons plus probes could have held off the marines, but it would have needed coordination and micro beyond the state of the art. Instead Bereaver lost its natural and was set back.

Iron tried to force the ramp while expanding, but didn’t have a big enough edge and was pushed back. Bereaver counterattacked and tried to get ahead with a double expansion, but tanks came out and Bereaver was never able to catch up. Bereaver strangely made a robo support bay early but did not build any reavers until much later, adding to its disadvantage—this game was played before the reupload below.

The dragoon opening is still sound against barracks play. Dragoons are versatile. But fighting the infantry calls for excellent micro with focus fire, and even Bereaver is lacking. Skynet is fairly skilled, but Iron’s new opening smashes it.

Bereaver

Bereaver was reuploaded yesterday. The new version’s first game was against Tyr by Simon Prins, and I immediately saw plays I hadn’t seen it make before. Bereaver went double robo.

Bereaver’s shuttle-reaver micro is not fluid like ZerGreenBot’s, but sharply goal-directed. Tyr vainly struggled to save itself, not realizing that it had to cover the reaver drop zones and come up with some kind of air defense. Every time Tyr unsieged, the reaver dropped, fired, was picked up instantly, the scarab skirted around the minerals—boom. By the time the second shuttle appeared with 1 zealot inside, it was already too late for terran.

The tanks at the top are approaching, too late to defend. As for reaver shots, sometimes they dud out. And sometimes they do this.

Reaver drop is crazy complicated. In time, I expect Bereaver to learn how to drop in the teeth of sieged tanks: Drop a zealot first. Tanks fire. Zealot says “ow!” Reaver drops and has time to fire before the tanks can reload. Terran defense has to be on the ball!

Bereaver continues to score wins against its top rivals, but I’m not sure whether it has reached #1 on SSCAIT. Krasi0 and Iron dominate the weaker bots, winning nearly all games, while Bereaver still drops some games to them. It takes time and effort to make a bot solid against all the different strategies!

Bereaver loses some games to protoss bots with strong macro, such as Skynet, when Bereaver takes its natural too late. It can also lose to unusual strategies like XIMP’s carriers. Here Bereaver storms the carriers and takes their shields off—it wasn’t enough, they still had all their hit points. After a long fight, XIMP recorded the win.

Bereaver’s zergling rush defense seems to work well against ZZZKBot, but shows weaknesses against variations. Here Zia opened 5 pool and, unlike ZZZKBot which suffered some pathing errors, immediately broke Bereaver’s ramp. The cannon-probe defense was firm and Bereaver held easily. So far so sound.

But while ZZZKBot does the fastest possible 4 pool and can only follow up by sending more lings, Zia switched to drone production and teched to mutalisks off of 1 hatchery. There is no strong followup to a failed 5 pool and Bereaver could have shrugged off the weak air attack... if it hadn’t restricted its production to zealots. Even so, the zealots could have won the game if they had attacked instead of holding their ground.

Bereaver still put up a fight, but Zia added to its mutalisk numbers and finally won.

Against Overkill’s 9 pool, Bereaver still canceled its gateway at the first sight of the spawning pool, before the scouting probe had traveled far enough to see the drones. It was not a sound reaction to 9 pool. After losing the blocking probes, protoss was already behind in economy. Overkill aggressively went after more probes, and despite poor play later was ahead the whole game and won as it should.

Notice Bereaver’s supply. With only 6 probes, it was impossible to catch up.

Bereaver is mounting a strong challenge for #1 on SSCAIT, and may have already reached it. It has been scoring wins against most of its rivals, including Krasi0, Iron, LetaBot and Tscmoo versions, and ZZZKBot. I haven’t seen a win against KillerBot, though.

Bereaver’s favored game plan is to outmacro its opponent and win with repeated direct frontal attacks, “damn the torpedoes” style. Against strong defenders like Krasi0 and IceBot that can lead to long games, but they aren’t strategically interesting.

Here Bereaver has defeated Krasio’s slightly sloppy early push in the center and broken into the terran natural. The zealots ignored the defending vultures and killed all the SCVs, bringing a quick win.

Bereaver has adequate skills with storm and reavers. Both could stand to be improved (but what couldn’t?). It knows how to cannon a ramp for defense (the early error where the cannons blocked the path is fixed). I think its most impressive special skill is entrance blocking, as here. It forms the zealot block with smooth ease, and dissolves it just as easily when it wants to let units through. It’s nothing compared to ZerGreenBot’s special skills of reaver drop, zealot bombing, and overlord hunting, but Bereaver is much stronger overall.

Bereaver plays a different strategy against ZZZKBot’s 4 pool. As soon as it scouts the rush, it blocks its entrance with probes. Here it blocked the entrance much too early, while the zerglings were still in their eggs, and lost mining time needlessly.

Then it cancels its gateway, starts a forge instead, and cannons its main. The plan seems successful. It’s slow, but who cares about that when you win? The probe block is tight. The lings tend to suffer pathfinding failure and wander, but may soon kill a probe to break through, as here. The probes fought back, as you can see by the blood.

Then Bereaver pulls probes to defend its cannons and easily holds. With its probe skills, it is not in any danger whatever. After this it can build up and win at its leisure.

ZerGreenBot has been updated repeatedly, and now plays a richer game. I liked its PvZ best; it opens with a forge fast expand and follows up with corsairs, reavers, and zealots, a strategy that is somewhat similar to mainline human play.

Here are shots from a game on Benzene against Tscmoo zerg. ZerGreenBot opened pylon, forge, cannon, nexus, gateway, cannon. It looks to me like a sound wall-in in the correct place (a couple spots need blocking units to be tight). On maps that don’t allow a wall-in, like Destination, it necessarily builds something looser.

ZerGreenBot’s first tech choice at the next level was stargate, starting air attack +1 before the stargate finished warping. Normal would be ground attack +1, but its choice seemed justified because the corsairs killed overlords throughout the game despite determined resistance. ZerGreenBot still tries its reaver drops versus zerg, but overlord hunting has become its top skill.

Unfortunately ZerGreenBot’s ground units fought so poorly that their code must be buggy. Even the air units showed some stuck-in-a-loop behaviors. Tscmoo won a crushing ground victory in the center and easily took it home. If its author keeps up the good work, though, ZerGreenBot is a threat to reach the top ranks. It has reaver drop and overlord hunting skills beyond any other bot. I think it also has the best protoss wall.

Meanwhile, Bereaver is already a top bot. I watched it battle Tscmoo protoss on the 2-player map Destination. Bereaver made an ill-advised attack across the bridges into Tscmoo’s natural and lost too much army. Tscmoo should have consolidated its advantage by expanding and containing, but instead tried to cash it in immediately with its own attack across Bereaver’s bridges. It could have worked against a weaker bot, but Bereaver defended efficiently with cannons, a reaver, and a handful of troops. Tscmoo overpressed, fell behind, and lost. It was a decent win against a tough opponent.

Next: SSCAIT map comparisons.

Wow, did you see the new protoss bot Bereaver? It was uploaded today at SSCAIT. In its first game it failed to start (oops). But in its second game it played strikingly well against Krasi0, breaking Krasi0’s bunker in the early game even while expanding and teching; Krasi0 defended well and held, of course, because that’s what Krasi0 does. Then Bereaver put up a fierce fight in the middle game with reavers and high templar, repeatedly wearing down and breaking Krasi0’s pushes until Bereaver ran out of resources, unable to expand beyond its third in the face of terran map control.

Somebody with game-scheduling power must have seen the game too, because games against other top bots came up right away. Bereaver lost more than it won, but it did defeat IceBot despite misplacing its natural nexus and being unable to take a third, ignorant of how to clear the mine blocking the expansion spot.

I was also impressed with the game against Andrew Smith’s Skynet. Bereaver apparently diagnosed Skynet’s dark templar rush and prepared against it, cannoning and easily holding its ramp. The cannons were misplaced and blocked dragoons and reavers inside, a fatal blunder, but the basic skill is there.

It’s a great start for a new bot. Many rough edges are in plain sight, which means that improvements should come easily!