Starcraft AI blog

I have decided what tactical skills to work on. My list included skills for specific units: Mutalisks, the most important; lurkers, which I’m most interested in for now; scourge, which Steamhammer spends heavy gas on and doesn’t always use well, defiler skills because Steamhammer often reaches late game. But those are only single unit types. And unit coordination skills, like storm dodging, scarab dodging, mine clearing and mine dragging, making the best use of the dark swarm that is on the map—all needed, all narrow and specific. And tactical analysis, my initial favorite. I have an algorithm in mind, which calls for a fast combat evaluator. MaasCraft’s tactical search also uses a fast combat evaluator. My idea is different, and I’m not satisfied with MaasCraft’s evaluator. Thinking through what’s needed, I concluded that the first draft would be easy to write, but would produce poor results. I think it’s likely that it needs a sophisticated combat evaluator to work well—I have an AI algorithm in mind for that too, but I fear I can’t finish it in time for SSCAIT in December.

To make the most progress before SSCAIT, I decided to work on the next level of pathfinding skills. Steamhammer currently calculates terrain paths without regard to where the enemy may be. On an empty map, ground units reach their destinations without getting stuck on terrain. When a unit is trying to reach its destination safely despite the enemy, a scouting unit or a drone transferring to another base, the unit reacts to dangers by leaving its path and running away from the enemy. It is not able to figure out a way around (though it may blunder into one), and it is not able to tell when its path is completely blocked and it should give up. So overlords scout less safely and less efficiently than they could, and worse, drones trying to transfer may end up burrowed all over the map, wasting supply and risking their lives to achieve nothing.

Steamhammer needs true safe pathfinding. It has to recalculate safe paths when the enemy is sighted. That opens the door to a lot of more specific skills.

• Don’t send drones to a place you know they can’t reach. This alone would save many games.
• Don’t even spawn extra drones inside a tight contain. They won’t get out.
• Better scouting, from maneuvering the early scouting worker to moving overlords and the Recon squad.
• Calculate least-danger paths for harassment. You can take hits as long as you escape.
• Similarly for drops.
• Reach safe spots to attack walls or other stuff from outside enemy range.
• Enemy vision is a kind of danger too. Find sneaky paths.
• Path through nydus canals. Nydus canals are part of my plan to support islands.

I don’t know how many of these I’ll get to by SSCAIT. There is a lot to it: Ground units and air units have different needs, safe paths and least-danger paths are different, sneaky paths are different. Safe drone transfers are the biggest weakness and have top priority. Part of the solution is to spread hatcheries out more, rather than putting all macro hatcheries in the main.

The first part of the job was to create a task manager to run background tasks. It’s simple, I wrote it yesterday. The idea is that pathfinding tasks will update safe pathfinding data structures behind the scenes, so that the calculation load is spread out and the data is reasonably up-to-date. Over time, I expect to add a lot of other kinds of tasks. Steamhammer runs fast, and for now there is little risk of overstepping the frame time limit. (Even in the late game when maxed, most frames take a handful of milliseconds, and spikes above 20ms are rare.) But I have thought up plenty of complicated tasks, and it seems likely to become an issue someday. I want the infrastructure to be ready, so that I can implement a principled solution instead of refactoring a lot of code when the day arrives.