Starcraft AI blog

Time for another Steamhammer update. The key bug still has me frustrated. Some of my recent progress:

Base placement. The UAlbertaBot base placement algorithm that I borrowed works perfectly on most bases, but turns out to have a flaw. For some unusual base layouts, it places the resource depot far from the minerals. For example, all other bases are good on Moon Glaive, but the 1 o’clock base sets the geyser at an unusual angle to the intended base location. The algorithm places the base level with the geyser and far from the minerals, away from the intended location.

I’ll look into it more before deciding how to fix it. I might keep the algorithm as is and add an optimization step that slides the base to a better location. Or it might be simpler to ditch it and use a distance minimization measure directly.

New openings. Looking ahead to the near (ish) future when Steamhammer gets its tree of openings, I added 4 new openings. In the tree, they will be forks of existing openings and will offer opportunities to make late decisions based on scouting information. I added 1 ZvT, 1 ZvP, and 2 ZvZ choices. Before the tree arrives, I’m likely to add more forks. It would be natural to have a wide variety of overpool followups for different situations.

Even in the upcoming version, once I add fine-tuning of opening choice to the opponent model, the new openings should be worth having. They will counter some opponents more sharply.

Squad mixup bug. Today, tired of other things, I arbitrarily decided to fix a bug in squad membership. It’s not an important weakness, but it’s been bothering me for months, so I picked it.

The problem is that sometimes units that should be in the flying squad get stuck permanently in the ground squad. 3 unit types are special for squad assignment: Scourge, devourers, and carriers. If there is a flying squad with other flying units, then these types go into the flying squad, otherwise into the ground squad. The theory is that these units should coordinate with whatever squad exists—especially devourers, which are support units. The bug is that, if one of these units is assigned to the ground squad—usually because the flying squad was temporarily wiped out—it stays there. When the flying squad is reconstituted, it doesn’t move back.

The bug was easy to find, but I decided that the underlying problem was that the code was too complicated. I simplified and rewrote it until it was Obviously Correct and there could not be any bugs left. Nevertheless, there was one bug left, and I had to fix that too. Not quite simple enough; maybe next lifetime.

I’m not sure whether this fix improves strength. If you’re playing with mutalisks and zerglings and the two tend to act independently and go to different places, maybe scourge should not always be with the mutalisks. At least, stream watchers are not likely to notice the different behavior; it’s hard to see unless you know what to look for. Anyway, now it works as designed, and since the code is clearer it should be easier to change the behavior if it turns out to be weak. Still a net improvement.