Starcraft AI blog

It looks as though Steamhammer 2.2 with regions and without BWTA will likely not be ready right after SSCAIT finishes, as I had planned. It will take longer because more stuff needs fixing. For one example, today Steamhammer lost versus UITtest because of a bug where drones entirely stopped mining minerals. I currently have WorkerManager instrumented to the gills to trace it. For another, yesterday I fixed several causes of rare production freezes and also added a workaround for the serious macro glitch that happens when Steamhammer wants to spend a lot of gas and is collecting gas slowly. Game-losing bugs like this are second on my priority list after crashes.

Also on my list is a bug that can cause infinite creep colonies to be built in the main base, instead of a limited number in the natural for defense. And I want to get the second building construction delay bug; fixing the first one got the spawning pool to start earlier, but the spire seems to start later, and that loses games too.

Plus of course I have added a few openings and made the usual varied fixes and changes. I always do.

high and low ground

In my current implementation, regions are defined entirely by chokes, which are themselves defined as narrow places in the terrain. I’m considering whether to change the definition of chokes to include changes in ground level. A narrow ramp counts as a choke no matter what. I’m thinking that maybe a wide ramp should also count as a choke. It has a similar property of defensibility; the difference is that the defensibility is asymmetric: It is easier to hold the top than the bottom. Since it’s defensible you care about it and may want to treat it as a region edge, no matter which side you’re on.

pathfinding

I’m not going to do pathfinding right away (though I’ll likely take initial steps soon), but here is my current plan. I want to separate high-level and low-level pathfinding. A high-level path from A to B is a sequence of chokes to go through, basically the same as BWEM provides. If you’re already in the same region, the sequence is empty. A low-level path is a sequence of positions to go through. A high-level path can be planned fast and if necessary replanned fast. A low-level path has to attend to details, so it saves time if you never have to plan farther ahead than the next choke, especially if you may change your mind.

For high-level pathfinding, Steamhammer needs to know all the chokes and whether each one is open or closed at last report. Therefore chokes must be found without destructible map obstacles (not how my current implementation works), and then each choke analyzed to see whether it is blocked. I also want to know the choke width, in case not all units fit through, to play on maps like Third World with narrow ramps and Blue Storm with a narrow entrance. For threat-aware high-level paths, it needs a measure of threat for each region and/or choke.

For low-level pathfinding, I want to work at the 32x32 tile level as much as possible, because the 8x8 walk tiles are 16 times as much data. I thought of scaling the “how much room is around this walk tile?” data to tile size, taking the max of the walk tile room values within the tile and filling in that as the room around the tile, perhaps with forcing to zero if the value is small or other adjustments. Other grids will also be at tile scale: This tile is blocked by a building, the threat at this tile is such-and-such. A path could be found at tile level, and any tricky parts double checked at finer resolution if necessary.

For air units, regions don’t matter and probably all path planning can be done at tile scale. Then detailed movement decisions related to firing and cooldown will be made frame by frame at pixel scale as now.

zones? areas?

In related news, I’m thinking of changing the name “regions”. Starcraft has its own idea of regions, represented by BWAPI::Region objects. They work differently and Steamhammer currently doesn’t use them, but they could be useful for some purposes. It would be nice to avoid a name clash, so that when you see a variable named region you don’t have to look up the type to find out what it is.

I like short names, so I’m thinking Zone or Area. Any other suggestions?