Starcraft AI blog

I enjoyed the game TyrProtoss vs Simplicity on Benzene. Simplicity is not ranked high, but it plays some good games.

I thought that Proxy versus Tyr by Simon Prins was a good game to draw lessons from. It’s strategically simple and has a clear turning point.

Tyr played a Giant Terran Death Ball Will Crush You strategy, macroing up a juggernaut of tanks and marines before moving out. That gave Proxy time to do its thing and develop a roaring economy, in the meantime frittering away a few units in light harassment. Proxy went with a lurker-ling mix. When Tyr moved out, Proxy attacked repeatedly to little avail, looking almost helpless in the face of terran might. Zerg slowed the terran force but could not harm it much, fighting inefficiently and losing units at a high rate. Then suddenly the terran ball unraveled and the game was all Proxy. What happened?

Lesson 1. When Tyr’s force reached the bridges to the enemy natural, it became disorganized trying to move through the narrow choke. That’s the main reason the game was lost. At the same time, Proxy’s forces, trying to approach from all angles, concentrated their attack more effectively. I suppose that’s partly due to the map configuration and mostly due to Proxy realizing that it could attack the disorganized terrans with advantage.

The lesson is that movement is a big deal. Moving units around the map is important and difficult in itself. Bots struggle with moving around in good formation, and in difficult terrain they have no idea how to adapt. For the first micro skill that I implement with machine learning, I am seriously considering the skill of moving squads from place to place.

Lesson 2. Don’t waste units–well, it’s empty advice, everybody knows that. But look how many units Proxy lost needlessly before the decisive engagement. It could afford the losses because of its strong economy and strong macro, and fighting when it did was not wrong, because it slowed the terran down. But if Proxy had fought efficiently, the terran ball would have been broken in the middle of the map, not perilously near the zerg natural. Steamhammer desperately needs to learn this lesson.

More a suggestion than a lesson. I think terran did not take full advantage of the situation, and I don’t mean only neglecting to get stim. Leaving aside the need for terran to take a third itself, when zerg spreads to a large number of bases, terran should be thinking “how can zerg defend all that?” In this game, Proxy went all ground with no air defense. If I were the terran, I would have made a couple dropships: Drop marines and medics off to one side, stim, run in and eradicate drones, then focus on the hatchery. When defenders appear, fight them if you like, or else pick up and drop another base. If zerg invests in defending the many bases, the cost will be far more than you spent to harass them. The terran ball will be a little weaker, or will move out later, but zerg will be substantially weaker.

Steamhammer and Tyr terran by Simon Prins played a hilarious game on Moon Glaive. I think that Steamhammer decided on a 3 hatchery before spawning pool build (it’s not entirely clear), but the zerg build became confused because Tyr’s scouting SCV delayed the natural hatchery, and because Steamhammer has an issue on this map where it sometimes sets its bases down unexpectedly far away. The build as executed was hatchery-pool-hatchery, with the third hatchery in Tyr’s natural because zerg hadn’t located the enemy yet. Something similar happened almost exactly a year ago in a game versus Krasi0.

Tyr reacted differently than Krasi0: Tyr ignored the zerg base in its natural!

The marines fired at the zerglings, but the hatchery and drones were in plain sight, and they just didn’t care. Their job, I gather, was to guard the natural against zerg attack, and the functioning zerg base was not an attack. They took their orders literally! Steamhammer was also unworried, and mined minerals contentedly.

Tyr was bright enough to figure out that it had to expand somewhere else, and planted a command center at what would normally be its 3rd base position. The zerg play was disorganized, but the terran play was more disorganized, and Steamhammer won effortlessly.

A funny game, a comedy of errors: Steamhammer versus Tyr terran by Simon Prins, on the map Tau Cross. Steamhammer opened with 2 hatch mutalisks, and Tyr bunkered itself in and went with infantry on one base.

Phase 1: Steamhammer fiddled around with its mutalisk force, picking off several building SCVs but mostly wasting time.

Phase 2: Steamhammer happened to notice that the terran mineral line was also a possible target. “Oh, look, terran has SCVs mining. I didn’t know that!” Tyr didn’t defend but moved out to counter instead and lost all SCVs. Steamhammer had 3 mining bases to 0, and only had to survive Tyr’s attack to win. Terran could not reinforce, so that was easy, right?

Phase 3: Instead of defending itself, Steamhammer decided to sacrifice every mutalisk against the meaningless bunker. It also wasted units piecemeal against the terran ball. Tyr destroyed the zerg main and natural. Steamhammer lost many drones by sending them to mine gas at bases that were under attack. That makes 3 big mistakes, more than enough to lose.

Phase 4: Tyr spread out to find the zerg 3rd base, found it after a few tries, and then—decided to send its army home to rest. “No zerg anywhere! Not that I’ll admit, anyway.” The marines in the picture saw the base, and that is when Tyr started to send its troops home.

Phase 5: Steamhammer slowly recovered from 7 drones at its third base. It restarted its tech from zero, put down 4 sunkens because it knew there was a scary army out there, and belatedly switched to lurkers. Steamhammer made far too many drones before moving out, but finally sent a lurker and won easily because Tyr had no detection. The mutalisks had also killed the comsat.

In the picture, nothing can stop the lurker, and more lurkers will come. You can see in the minimap that Steamhammer has retaken its main and natural and a mineral only base as well.

Both sides showed a lack of resilience. This time, Tyr turned out to be lacking a little more. Besides its opportunity to attack and win, Tyr had an unfinished science facility that it could have canceled (it’s in the upper right of the last picture). Then it would have had the resources to make an SCV and get back to mining.

Here Tscmoo has discovered that Tyr built near the edge of its low-ground main base and is vulnerable to attack from outside. Blasting down buildings with no losses helped Tscmoo in its easy win.

Did Tscmoo’s tank just happen to wander into a good position, or did Tscmoo analyze the situation to find the opportunity?

Noticing when you can shoot across a barrier is a great skill. I’ve seen other bots miss chances for free kills with tanks and even with dragoons. And it’s not hard—all you have to do is figure out what’s in range from where, and recognize simple cases where it gives you an advantage. Human players are always on the lookout for chances like that.

In a game last month, Tyr by Simon Prins was winning until this happened.

Pro tip:Don’t do that. The Great Wall doesn’t keep barbarians out, it keeps you in. The protoss bot by Roman Danielis dropped a dark templar inside the base from a shuttle and cleaned house. (You thought that a dark templar carried a warp blade? This one had a mop.)

I shouldn’t pick on Tyr—I think Tyr is above average in placing its depots in tight clumps along the edge of its base. It hit a bug this time, and I think the bug has been fixed. Building placement is hard, and it’s especially hard if you are terran, because terran bases need a lot of room for production buildings and supply depots. Some bots space all buildings apart from each other so that there’s a gap between any two and blocking is impossible. Terran bots that do that end up running out of room and having to build depots and factories outside the base in vulnerable open areas. Here ICEbot spaced out the buildings in its main and its construction had to spill into the map.

The fancy solution is do a path analysis in deciding on building placement. Does it block units off from anywhere they need to get to? Can fresh units get to the front without threading a maze? The analysis will be trivial sometimes, but not when the base starts filling up. PerfectBot will analyze both its own and its opponent’s building placement, for both attack and defense. “Oh, the opponent built an obstacle course. The enemy army is here so I’ll drop there.”

Knowing when the opponent has built a wall is a valuable skill—notice how well LetaBot’s ramp wall-in works against many opponents. If you don’t want to do real pathfinding around buildings, you could try to recognize a wall when your units fail to make progress toward their goal. I’m not sure it’s easier and I’m pretty sure it works less well, but monitoring progress toward goals is a good idea regardless. Units that find themselves behind a wall may want to destroy a building in the wall, without caring whether the building is enemy or friendly. Tyr could have won if it had opened its own wall.

Most bots probably rely on heuristics to place buildings so that they rarely cause problems. Nothing wrong with that; it should work well enough and it will be easy, and there’s a lot to do so ease counts. But I hope a few authors will go for more ambitious solutions.

SSCAIT has binary bot downloads on the Bots & Results page. Binaries are of course most safely executed inside a virtual machine.

Iron has continued to make progress but hasn’t yet lived up to its author’s hopes. It can now expand to its natural, though not beyond. Its game plan amounts to setting an elastic containment outside the enemy base, but its unit mix is not adaptive. An enemy that finds the right counter-mix and keeps pressure up can push the contain back and either break through or starve Iron out. Aggressive tscmoo zerg can’t be contained at all.

Tscmoo terran now knows how to kill tanks by laying mines next to them. The technique seems deadly effective. I also saw it chase down overlords with Napoleonic vigor, though only after the zerg was already toast.

Krasi0 and especially Tyr have both been playing more strongly after updates. I can’t pin down what they’re doing better, though.

Hmm, 4 terrans. Are we in for a terran renaissance?