Starcraft AI blog

Steamhammer-Joon is a funny game played today on SCHNAIL. (The player’s screen name is ZI7HMI and the game time was 21-06-30 08:48:50.) Steamhammer had played this opponent once before and correctly predicted cheese, so it started with 9 pool and a sunken in its main. Joon, being a crafty human rather than a bot, crossed this plan up by bunkering the natural below the ramp. At the time of this picture, the first terran barracks had lifted because it had started to burn, and the initial zerglings that escaped before the bunker were attacking SCVs.

Zerg was mining with more workers than terran, but was contained to its base—and terran sent most of the pulled SCVs back home, putting the human ahead in economy. Steamhammer kept sacrificing drones to the bunkers as it tried to expand (it’s on my list to fix soon with safe pathfinding), and losing overlords for lack of understanding of enemy visibility. But it also got lurkers, and terran was only just adding comsats. After a sharp struggle whose outcome looked uncertain at first, zerg broke its own natural—where terran had built a command center—and forced buildings to lift.

Now terran was far ahead in economy though with hands too slow to spend it, while zerg was ahead in army. Notice that terran is adding a starport while zerg is getting a spire. The zerg force, finding no buildings on the ground and unable to attack air, hurried across the map to the terran side. Immediately, Joon landed the buildings again, so that the drone which came down to expand could not take the natural but had to continue to another base to expand. Having crossed the map, lurkers forced the terran natural into the air and continued on to pillage the main, while terran quickly trained marines in the zerg natural and easily held it, restoring the containment—but with zerg already owning a base outside it.

In the picture you can see 2 vultures and a wraith, which proved of little value. Steamhammer scourged the wraith and a followup wraith (you can see the scourge in the production tab). At the opposite corner of the map, terran marines were supreme and Steamhammer chose a mutalisk switch, which was also of little value. The strategic situation completely reversed in a short time, with zerg ahead in economy and terran stronger in army. Steamhammer had taken the top center base, but was not mining there.

Steamhammer killed all SCVs in the terran main, left 1 lurker there to finish cleaning up, and returned the other 3 to visit the terran complex at the zerg natural. At the same time, the strong terran infantry easily broke the sunken in the zerg main, which had been waiting there since the early opening, and set about their own cleanup. Base race!

A crazy game, and a close one. Both players had opportunities to turn events in their favor at multiple points. I won’t spoil the end, though it’s predictable if you know how terran-zerg base races go. You can watch it to see.

The registered competitors for CoG 2021 were announced a few days ago on the results page. The submission deadline is not until 25 July.

Here are the new entrants. I sorted them in order of their current BASIL rank, which is a fair guess at how the tournament may work out.

• BananaBrain
• Stardust
• Microwave
• McRave
• CUNYbot (aka Bryan Weber)
• Granite

As I write, BananaBrain and Stardust are rated identically on BASIL, at 3068 elo. BananaBrain has fallen a bit; recently it was higher. I think it is likely that Stardust will get a tournament update, since it hasn’t had a public update in half a year. BananaBrain has had frequent updates and is closer to current. If so, then Stardust remains the favorite to hold its #1 finish. But BananaBrain has improved a lot, and tournaments are decided by results, not predictions! CUNYbot is the baby here, rated about 200 elo lower than McRave zerg. But it also has gone a long time without updates, and I don’t expect it to play without a tournament update—plus it showed strong improvement before updates paused. It may be able to hold itself off the floor.

Granite is a new name. CoG does not list authors or any other info, so I know nothing more about it. Historically, new names are often disappointing, but occasionally one is great. I have hope.

Here are the carryovers. PurpleWave is last year’s version (I expect that Purple Dan is not satisfied with progress). The others are being carried over for the second year. I sorted these by their finish in CoG 2020.

• PurpleWave
• BetaStar
• XiaoYi
• MetaBot

That makes 6 protoss, 3 zerg, and 1 meager terran (the same lonely terran as last year), and the terran scored only 37% in last year’s tournament. The race balance is lopsided. XiaoYi and MetaBot are likely to end up as punching bags that stronger bots try to score almost perfectly against.

Last year, 8 bots competed. This year, 10 bots are expected. But one constant has been that not all registrants end up submitting an acceptable bot—last year also had 10 bots expected, and 2 dropped out. Maybe this year will be better?

In TvZ, sometimes terran stops marine production and goes with factory units (maybe with starport units), whether early in the game to play a straight mech strategy or later to switch to it. Usually terran lifts the barracks to get it or them out of the way. If you see a lifted barracks, that’s a clue to the enemy strategy. Seeing vultures or goliaths appear may be your first clue, but unavailable barracks say that marine production is stopped (or at least slowed), so it’s a stronger clue. It rules out marine-tank unit mixes.

I think human players can usually read the clue correctly, when they need to. Bot opponents go marine-tank often, so it may be a useful clue for bots. But it seems a little tricky to read with assurance. You can’t just say, “overlord spotted a lifted barracks, cancel lurkers,” you need to look at more context. Maybe terran is only rearranging their base, or moving the barracks to a blocking position for the sim city. (Though if it’s in a blocking position, you may see whether it is making units.) Even a floating barracks far from the terran base may be intended to land as a proxy, maybe making a couple firebats to toast some drones.

Maybe bots should take a graded approach. Early in the game, terran should have only 1 or 2 barracks. Seeing a barracks in the air is a big deal, and the longer it floats or otherwise produces nothing, the more sure you can be that infantry is deemphasized. Later in the game you should have a rough idea how many barracks terran may have tucked out of sight, or at least how many barracks the terran’s bases can support. The more flying barracks you see, the more confidence you should have that fresh marines will be few.

At least that’s what I would start with if I were coding it by hand. My plan is to draw inferences like that largely by machine learning.

Here’s a fun SCHNAIL game, Steamhammer-HitHat (screen name Joongwan). Steamhammer had played this opponent before, so it had an idea of what to expect and made an early sunken. The sunken is misplaced. The misplacement is better against other bots than correct placement, but you’ll see in the game why I call it a misplacement! After learning by the loser, the next game went differently. Another interesting game is this one on Fighting Spirit against a different opponent.

I’m not sure why there are separate screen names and game names. The website comes with an API that gives the screen name with replay, and the replay has the game name, so no information is hidden. Still, people use the feature a lot, so it must have appeal. Are names that much fun? I’m guessing it was a feature added at the request of players. I sure wouldn’t have thought of it.

Steamhammer 3.5.1 is progressing, though slowly. Since my energy ran down, I stopped working on my plan of using Steamhammer’s new opening data. After seeing many SCHNAIL games, I’m mostly making changes to improve Steamhammer’s play against humans. Humans know a lot of tricks that bots don’t know, and they’ve uncovered weaknesses that I want to fix. Better is better, even when it may not show against bot opponents.

I rewrote Steamhammer’s crufty old code for deciding when, and in what bases, to place sunkens and spores. Unlike bots, humans are quite good at attacking vulnerable bases first. (Steamhammer makes an attempt to get this right. Most bots don’t try.) I was running the first tests, demonstrating that it worked in a couple of simple situations, when I realized that I should have generalized it for all races. Terran and protoss desperately need the skills: Make mutas and win because terran doesn’t add turrets; make DTs and win because only one base gets turrets or cannons for detection. I’m not only working slowly, I’m thinking slowly.... I rearchitected it and rewrote nearly all the code a second time, in a new StaticDefense class. It’s cleaner and more capable, and should be easier to adjust. It’s just now ready to get back to testing.

Humans make very different opening choices than bots. Most stick with general-purpose safe openings; a few specialize in cheese. I don’t have any way to collect SCHNAIL opening data, so I started a new file to hand-write an anti-human configuration. I didn’t fill in much of it yet, but I’ll get to it.

I expect my tweaks and new features to help somewhat on SCHNAIL and a tiny bit on BASIL. But we’ll see.

My energy is low, but I’m still working on Steamhammer and checking out games. Crazyhammer is Steamhammer configured to choose purely at random from its library of over 200 zerg openings. It plays only on SCHNAIL, and only practice games, because it’s just for fun.

Crazyhammer doesn’t get many games, and it loses a lot because its builds are often hilariously inappropriate. As you’d expect! Today Crazyhammer played a fun game against terran TeChRapy on Fighting Spirit. Crazyhammer randomly chose its queen rush build, which will happen about 0.45% of the time—this is the first time I’ve seen Crazyhammer play it in a real game, though Steamhammer did give it a try versus Stardust in AIIDE 2020.

In the queen rush, Steamhammer makes 6 queens early on and researches broodling. It’s hard to think of an opponent plan that it counters. I don’t have the strength to take pictures and do the blow-by-blow, but here are a few points you might like to notice.

• Watch the swoopy way the queens fly around. It was the simplest idea I thought of to keep the queens apart so that they don’t often select the same target. It didn’t work this game! At about 9:30, 4 queens simultaneously and from different sides ensnared the same group of marines. I should bite the bullet and implement proper spell target tracking.

• Techrapy went with multiple barracks, no tanks. Nothing was worth a broodling, and the queens were useless at first.

• Crazyhammer reacted by researching ensnare and adding lurkers, both useful against marines. Techrapy got tanks against the lurkers, and then the queens had a broodling target.

• The queens sucked at staying safe. One of the 4 ensnaring queens retreated forward instead of backward, and got shot down. Later, 2 queens in a row flew into turret range and died trying to snipe the same tank.

• On the upside, the fast queen’s nest meant that the hive was not too slow. Defilers helped.

In the following game, Crazyhammer started with 8 hatchery 7 pool, and Techrapy won easily. Terrans at this level usually play a barracks-expand build which is safe against zergling openings, given scouting and a few easy reactions. Certainly safe facing Steamhammer’s level. In the queen game, maybe Techrapy was confused and made overcautious by the “unconventional” (aka bizarre) build.

Queens showed poorly this game, but I’ve been surprised how often they are successful. When terran turtles hard, Steamhammer’s queens can be as valuable as its defilers in breaking the shell. Knowing that queens are in play tends to make terrans spend on air defense and move around more slowly and cautiously. And I know what I need to do to make them more effective.