Starcraft AI blog

I’ve been testing out Steamhammer’s new opening plan recognition to get a feel for it. I can summarize my findings in 2 points:

1. Recognizing the enemy opening plan works pretty well.
2. The reaction to the enemy’s plan is not easy to get right.

Right now, Steamhammer (development version) recognizes a half dozen different enemy opening plans. I’m likely to add or remove or switch around the recognized plans before release; it is still in an experimental state. The set of plans is not supposed to be exhaustive, because if Steamhammer’s usual behavior will do fine against some plan, then there is no need to recognize that plan. I may change my mind about that the next time I rewrite the strategy boss.

Plan recognition makes few mistakes of commission. I mean that, once it has decided what the enemy is doing, in my tests so far it seems to rarely change its mind (which it’s allowed to do as much as it wants) and rarely be wrong. On the other hand, it easily makes mistakes of omission, leaving the plan as Unknown because it doesn’t have enough information to draw a firm conclusion. I think it will take experience to learn whether that is a good tradeoff. I may want to relax conditions or add smarts.

Reacting to the enemy’s plan is a different story. So far, Steamhammer has a special reaction to worker rushes only, not to any of the remaining 5 possible enemy plans.

Opening plan recognition has 2 points. One point is that it will (it doesn’t yet, but this step is easy) tie into the opponent model, so that an opponent which usually follows the same plan will face openings intended to counter it. Stone, starting from the second game, will face Steamhammer’s anti-worker-rush opening. The other point is that, if the enemy plays unpredictably, Steamhammer will try to react when it recognizes the plan. PurpleWave and Tscmoo have been sometimes playing worker rushes that Steamhammer loses to, because the live version reacts poorly.

I think I have it working well now, pending more tests, but I found it hard to optimize and debug the worker rush reaction. Only zerg tries to react specially, for now. When Steamhammer recognizes the worker rush, it checks its build order to see whether it is playing an opening that does the right thing. That way, if it is already playing an anti-worker-rush opening or one that behaves similarly for the moment, it will keep calm and carry on. If the build order does something else, like make too many drones, then Steamhammer breaks out of the book opening and falls back on the strategy boss’s idea of what to do. And the strategy boss now has a special idea of what to do about worker rushes, starting from whatever situation Steamhammer finds itself in.

It’s a complicated arrangement, and it was hard to get right. Reactions to other plans will work differently, but even so I doubt I’ll have time to implement more than 1 or 2 more before the SSCAIT deadline on 20 December.

The game info in the upper left corner of the screen includes a line “Opp Plan” with the recognized enemy opening plan, so that stream watchers will be able follow along when the version goes live. It starts out as “Unknown” and changes if and when Steamhammer recognizes the plan. I think “Opp Plan” is a poor description, but I haven’t found a short string that is better (so if you have an idea...).