Starcraft AI blog

I’ve been adding recognition of the enemy’s opening plan to Steamhammer, as part of the opponent model. Besides making the opponent model smarter, the OpponentPlan is directly valuable to the strategy boss. I’ve been concentrating on enemy plans that the strategy boss is clumsy in reacting to.

After writing recognition code for several plans, I already felt dissatisfied with how it works. It looks at buildings and timings, it counts bases, it notices if zerglings are out suspiciously early, all extremely basic stuff. “2 barracks and no gas, I know what’s coming next.” There is no “You should have a second pylon by now, where is it hiding?” and no “I see more zerglings than you can get from 1 hatchery, you must have 2.” Rich and complex inferences can be drawn from the game information, and the primitive code I wrote draws only simple ones.

So I looked at PurpleWave, which does opening recognition under the name of “fingerprinting”. PurpleWave tries to recognize specific openings for zerg and protoss: This is 4 pool, this is 12 pool, this is 10 hatch, etc. And the way it works is, at heart, the same as what I wrote in Steamhammer. It is written in a different style, but it checks almost exactly the same information.

The biggest difference is that Steamhammer does not try to recognize specific opening builds. I think there are too many, and some of the differences don’t matter. The OpponentPlan groups enemy openings into categories, like “this is a fast rush,” without distinguishing between 5 pool and other early pools, or even between 5 pool and 5 barracks and 5 gateway. 2 barracks no gas gets the same plan label as 2 gateways no gas. If you want to react differently to 2 barracks than to 2 gateways, that is for the strategy boss to figure out. I think the plan categories extract more information from the game and compress it into fewer labels for the rest of the code to handle.

Well, if PurpleWave gets away with it then I guess the primitive recognizers are good enough for now. Someday I hope to write a cleverer plan recognizer that draws the deep inferences, that (like a pro) knows when you’re trying to hide a base and triggers a goal to go look for it. Or that says “You’re proxying something and I don’t know what, but I don’t need to see it because the answer is to build turrets.”