Starcraft AI blog

Today I tested Steamhammer’s new base placement code, a major step in getting rid of BWTA2. There are still a couple of big bugs, but it works well most of the time. It’s getting close to ready.

As I mentioned when I first wrote about map analysis plans last June, Dave Churchill removed BWTA as a dependency from UAlbertaBot after Steamhammer forked from it. Newer UAlbertaBot versions do the necessary map analysis themselves, and when it comes to unnecessary map analysis, they simply delete some less important features that BWTA used to provide. I won’t delete features that add strength, but for the necessary features my plan has always been to borrow from UAlbertaBot.

Here’s how placing bases works in general. A base consists of a location for the resource depot, plus a set of minerals and vespene geysers belonging to the base (plus any other info you find useful). For starting positions that a player may begin the game in, the map specifies where the resource depot goes. BWAPI passes the information through. You still have to figure out which resources belong to the base. I had Steamhammer assign all the resources within a fixed distance to each starting base, and it works fine.

For other bases, software is on its own. First, group the resources on the map into clusters, expecting that each cluster will become a base location. You probably want to skip over blocking minerals and any clusters that don’t provide enough resources to be worth placing a base at, or at least handle them differently. Then, for each cluster, figure out the best place to put the resource depot so that mining will be efficient. Details matter, but it’s not complicated, at least if you ignore weird maps like Crystallis.

I wrote my own clustering, which is simpler than UAlbertaBot’s (though I wonder if I made it too simple and crude). For placing the resource depot, I followed UAlbertaBot’s way. UAlbertaBot provides 2 methods, one of which is commented out. The commented out method finds the center of the resources by averaging their locations. (Technically, it’s the centroid.) It then uses UAlbertaBot’s building placement code to find the nearest location to the center at which it is legal to build a resource depot—you have to be at a minimum distance from any minerals and gas. The building placement code calculates a spiral of tiles centered at the desired location and tries each one until it finds one that works.

The active method in UAlbertaBot, which I took for Steamhammer, is to find the center of the bounding box of the resources. That’s the desired location, and UAlbertaBot proceeds as above.

In practice, Steamhammer’s new code usually finds exactly the same base locations as BWTA. There are some exceptions. It finds 2 bases in the center base of Fighting Spirit (as some other bots do), which I think is due to a bug that assigns the same mineral patch to more than one base. I don’t expect it to be hard to fix.

Good progress so far.