Starcraft AI blog

This picture of Steamhammer versus XIMP by Tomas Vajda is a perfect illustration of why Steamhammer needs a smarter tactical analyzer.

The hydras decided that they had to retreat from the carriers at the top. Where to retreat to? “Hey, look, those scourge have found a great location! It’s a safe spot, it’s close to the enemy base—let’s go there!” It follows a heuristic of trying to keep its units together. It hardly needs saying that the entire hydra force was lost trying to run past the cannons. In big army games, Steamhammer makes similar blunders nearly every game.

The poor scourge play is another issue....

The picture also illustrates the silver lining to Steamhammer’s excessive retreating weakness in this version. Because Steamhammer now plays weakly when it is locally behind, it lost games playing the merely strong 3 hatch hydra opening that it had settled on in the previous version. It was forced to find an even stronger counter to XIMP, 3 hatch before pool into hydras. Look at the worker counts—even after losing this army, zerg is still ahead because its massive economy can replace the losses while protoss will remain unable to expand. Thanks more to XIMP’s objectively bad strategy than to Steamhammer’s play, and despite the severe blunder, Steamhammer put the game away easily.

I enjoyed this game of m-khan’s KaonBot versus XIMP by Tomas Vajda, showing another way to beat the carriers.

As I write, KaonBot is rated about 1900, so it is a slightly worse than average bot. I would say that it is at the high end of the low-ranking terran bots. KaonBot goes mass marines every game (with medics and upgrades), which is a severe limitation, but it has above-average smarts in adapting its economy to the situation. Against XIMP, KaonBot quickly took the entire map, except the island bases. XIMP could not get a third base because they were all taken!

Marines are deadly efficient at shooting down interceptors, because they do normal damage rather than explosive damage like goliaths, dragoons, or hydralisks. The picture shows marines fighting interceptors and cannons. The carriers could not keep interceptors in the air. This first infantry force was not enough to clear the cannons, but a later one was.

KaonBot seems to score around 50% against XIMP, which is pretty good.

Ways to beat XIMP, with example bots:

• cloaked wraiths - WOPR by Soeren Klett (with goliath-tank followup)
• goliaths - Krasi0
• marines - KaonBot
• tanks - Tyr by Simon Prins (wipe out the cannons before the carriers are out)
• ghosts - nobody yet?
• hydralisks - Killerbot by Marian Devecka
• hydra-scourge - UAlbertaBot by Dave Churchill (special build order for XIMP)
• ultralisks - Ailien (ignore the carriers, kill the bases)
• dragoons - Steamhammer playing protoss (with a 13 nexus build)

Protoss has the most trouble against the carriers, but when Randomhammer rolls protoss, it goes with a straightforward nexus-first build that produces enough units to break the cannons. AIUR does the same thing sometimes, though not as consistently. If you get far enough ahead in macro, it should be easy to win with almost any strategy.

It should be, but it isn’t always. Steamhammer zerg still struggles against XIMP, losing games due to several bugs and limitations. On 2-player maps Steamhammer doesn’t finish its opening build order, and depending on how it scouts, it may not make a spire (which makes the win easier). In the most recent game, Steamhammer took many bases and crushed XIMP’s natural and main with ultralisks, leaving only the protoss third, then lost by streaming ultra-ling into the empty protoss main to be slaughtered by carriers until zerg finally mined out. It’s a combination of a scouting limitation, a tactical limitation, and an expansion bug. Too much to fix!

AILien scored a fine win over XIMP. The game plan to defeat Tomas Vajda’s carrier bot:

1. Take 7 bases and grow a huge economy.
2. Prevent XIMP from expanding beyond its natural.
3. Don’t bother to fight the carriers, just accept losses. With enough units on the map, the carriers chose to destroy defenseless zerg units to protect protoss bases and did not visit a zerg base until too late.
4. When hive tech is ready, adrenal glands for the zerglings and the ultralisk upgrades, go win. Zerg can send units faster than protoss can kill them.

Ha ha, so simple! AILien made hydralisks, but I didn’t see them fire a shot against carriers or interceptors. That would have been too easy! No, XIMP is not properly put in its place unless zerg handicaps itself with buggy hydras!

I’m too busy to pull images, but watch the replay at the link. Let’s see how long the replay stays online.

Steamhammer 1.0 got to try both of its prepared strategies versus XIMP in close succession. Did somebody schedule the games?

In the first game (Brood War replay file), Steamhammer went mutalisks. XIMP counters with corsairs, so I was taking a risk. The strategy is inspired by Sijia Xu's Overkill, which plays a 2-hatch muta opening that smashes XIMP before protoss reacts.

Instead of a quick air attack like Overkill, Steamhammer went three hatch before pool and prepared a heavy blow. The build produces a large first wave. XIMP saw the lack of ground pressure and built fewer cannons than usual, only 5. The mutas started in on the cannons, but had only killed 2 before corsairs chased them away. With the slower build, XIMP was able to react correctly.

When Steamhammer has a spire and scouts air tech, it makes 1 pair of scourge as insurance. When it verifies enemy air units, it aims for exactly the right number of scourge to clear the enemy air force. The game became a muta-scourge versus corsair seesaw. XIMP saw air units and felt the need to keep investing in corsairs, so it could not make carriers. Steamhammer pruned back the corsair numbers with scourge, but was short of gas. Neither side could keep a large force in the air.

XIMP took a third, and Steamhammer took bases down the left side of the map, struggling to get more gas. But the new gas came online slowly, and zerg resorted to making zerglings—which is what it needed all along! The lings tore down the protoss natural, and then XIMP could not keep up. It was an entertaining game.

In the second game (Brood War replay file), Steamhammer went hydralisks, the safe and natural choice. Hydras attacked toward the protoss natural and danced with the cannons and carriers for a while, killing some cannons and then most interceptors. When enough hydras had accumulated, they cleared the cannons. At the same time, scourge arrived and exploded carriers. The game looked over.

But no, no easy win. Steamhammer hit a bug which made it unable to produce any more hydras. Scourge were able to hold off carriers for a while, but without ground attack there was no hope. Solving all the similar bugs is a major goal of version 1.1.

Today is the second and more interesting part of the SSCAIT 2016 round of 4. Krasi0 fought XIMP, with the winner to move on to the final. The loser went to a 3rd/4th place playoff match against Iron.

Krasi0 vs XIMP

Game 1 was on Empire of the Sun. XIMP is the carrier bot. Terran Krasi0 saw what was coming and chose to attack with tanks and early goliaths before the carriers had all their interceptors. The tanks were somewhat inefficient in sieging down the cannons (most bots are), but they were fast enough. XIMP was in trouble regardless, but losing too many probes sealed it.

Game 2 was on Heartbreak Ridge, a 2-player map. It has many cliffs which favor carriers, but it also has low-ground bases and a short ground distance between the mains, which favors mech attacks. Krasi0 attacked with the same timing as the previous game. Krasi0 again killed the natural, but terran reinforcements chose a path through the center which took them next to the protoss base, distracting XIMP into playing correctly against the reinforcements instead of the main terran force. Krasi0 could have sent fresh units the other way around the center of the map, where carriers could not have engaged them until they arrived. Then the mech army would have stayed compact.

But as it happened, the diversion toward reinforcements and Krasi0’s difficulty in attacking the protoss main through the very narrow entrance meant that the carriers were able to build up interceptor numbers. XIMP defeated the goliaths and started chasing the terrans away. Krasi0 sent goliaths piecemeal toward the front and lost them a few at a time.

While one carrier group fought terran units around the center, another group departed on XIMP’s trademark edge crawl to survey the bases around the map and attack from the rear, a slow but dangerous plan. Both players were in some trouble. XIMP had only its main left and no long future unless it could take and hold another base, while Krasi0 had 2 bases but not enough anti-air to stop the carriers. What would happen?

XIMP’s front carriers played poorly and lost numbers. They could have returned through the center to cover while XIMP retook its natural, or they could have joined the attack on the main where cluttered buildings made goliaths awkward, or they could have circled the terran natural and attacked it from above the cliff, but they insisted on attacking from the front without the advantage of a cliff. With that decision, Krasi0 had the lead. Terran should have sent its ground army, minus air defense, to the protoss base, which would either cause a base race or bring the carriers back home to defend. Instead Krasi0 left tanks and vultures idling around the center of the map. Krasi0 did not use its lead.

Neither side was making the most incisive moves, and the outcome was unforeseeable. Fun game!

Krasi0 got a third base up. XIMP had no money but destroyed the terran main, slowly. Krasi0 did not try to float its factories, but rebuilt from scratch instead. Finally Krasi0 built up enough stuff to start hitting carriers, and that was enough.

Both players fought like lions. After mistakes all around, the victory was narrow. Krasi0 won and went to the finals.

Lesson: You never know what little thing will make the difference. A small improvement by XIMP (try to attack from above cliffs, or destroy bases more efficiently) or a minor weakness in Krasi0 (build the 3rd too late, be unable to recover from losing all tech) could have given us a different result.

Iron vs XIMP

Iron is far more aggressive than Krasi0. Iron attacked with infantry and tanks, sieged down the cannons, held off carriers with marines and turrets, finally added valkyries almost as an insult, and won easily. The second game went about the same way. A group of carriers escaped and caused damage, but only until the undefended protoss base died.

It’s not easy to beat XIMP, or more bots would do it, but Iron made it look easy.

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.

I got my SSCAIT wish and saw the first Steamhammer versus Killerbot and Steamhammer versus XIMP games today.

Steamhammer versus Killerbot by Marian Devecka: Would my counter-build work? In my tests Steamhammer wins with it about half the time. Killerbot went with its +1 speed lings and Steamhammer opened 11 pool and held with its own slow lings while teching to lair. Timing is critical—12 pool is too slow on some maps! In this game Steamhammer managed to sneak in a drone kill while Killerbot’s lings were busy chasing the scouting drone (UAlbertaBot doesn’t do that natively, I had to improve the decision making). Steamhammer added 2 sunkens for protection while getting mutalisks—it still had only 1 hatchery, while Killerbot was headed for 3 hatcheries, and it is impossible to hold without static defense. Steamhammer’s first 3 mutalisks hatched and headed for the enemy base, and as soon as the flyers were safely out of range to intervene, Killerbot’s zerglings attacked! Steamhammer pulled drones to defend and lost every single drone, but the sunkens held and the base was left barren but secure for the moment. The 3 mutalisks killed all of Killerbot’s drones in return and then tore down the enemy zerg base with excruciating slowness—Steamhammer won a close game. Steamhammer-Killerbot games often go down to the wire like this in my testing; I’ve seen one side or the other win with only 1 or 2 buildings left bleeding onto the map. But without the special-purpose counter-build, Steamhammer loses every game; Killerbot is far superior in tactics and robustness.

Steamhammer versus XIMP by Tomas Vajda: Steamhammer opened with 3 hatcheries before pool, the only bot I’ve seen play this logical response to forge-expand. (Though I saw auxanic open unsoundly with 5 hatcheries before pool!) XIMP cannoned up for carriers, as always. I hadn’t tested this matchup, so I wasn’t sure what would happen. Steamhammer went hydras with +1 attack, and soon had enough to tear down the cannon wall (slightly before +1 finished, annoyingly), wipe out XIMP’s natural, and start on the main. That’s what I intended, and I’m pleased it worked. XIMP seemed about to fall, but suddenly the first carriers started to make a difference—they finally had enough interceptors. The hydras did not have critical mass to fight carriers and were cleared from the main. At this point, Steamhammer had 6 bases though not enough drones to saturate them, and XIMP was mining minerals with 6 probes and gas with 3. Steamhammer was still winning by a mile.

As the game went on, the carriers moved to the middle of the map and Steamhammer trickled hydras toward them, losing them a few at a time for no apparent gain. There were 2 obvious problems. First, Steamhammer only attacked interceptors; as I watched, I realized “carriers don’t attack, so they’re at the bottom in the target priority list.” The code is easy to rewrite, though I’m not sure what solution is best. And second, trickling the hydras in was suicidal. I concluded while watching that SparCraft must not know about carriers. It ignores units that it does not know about, so when asked to predict the combat outcome, SparCraft always reported “zerg wins,” and Steamhammer moved its hydras confidently to their deaths. That may be harder to fix.

Steamhammer then won when XIMP overstepped a time limit, taking too long on a frame. That was disappointing. :-( I’m not sure how the game would have turned out. Steamhammer was still ahead but was playing like an idiot, and XIMP did finally re-expand to its natural and may have been able to add carriers before Steamhammer could take the rest of the map and start to make progress.

After these two uncertain wins, Steamhammer played against protoss Ian Nicholas DaCosta, a weaker bot which it had beaten in their previous game. Steamhammer got unlucky with base positions and scouting, placed its 3rd hatchery directly on the path that zealots were taking toward its main, and lost. Luck runs both ways!

Today Iron learned how to keep expanding. I watched it starve out ICEbot, which is exactly how a contain is supposed to work. It’s moving fast, and may yet go over 90% win rate.

Update: I also watched a tense close game against XIMP. For half the game XIMP had no probes and 30 minerals but 8 carriers, while Iron had many bases that it could not defend. Would the carriers have to stay home to resist the pressure, or could they relieve it enough to go marauding? XIMP won, but I was unsure until near the end.