Starcraft AI blog

When I rewrote Steamhammer’s scouting, I tested it widely and thoroughly. I’m disappointed to find out that it still hides bugs, though the bugs only show up in a few games here and there. I’ve seen a couple games where the scouting overlord stops in an empty base, when it should continue to seek the enemy. Plus there is one other bug.

Watch the game Steamhammer-Bryan Weber on the 4 player map Roadrunner, which shows a hard-to-notice but potentially fatal scouting blunder. Bryan Weber played 5 pool while Steamhammer made a hatchery first, which could lead to a build order loss. Bryan Weber’s overlord scouted the correct base first, while Steamhammer’s went in the wrong direction. The situation is bad so far, but Steamhammer’s scouting drone has a chance to make up for it. Watch it leave the base at 2:10 in the game, quickly spot the enemy overlord, and immediately turn around and go home. It looks like the smart inference paid off! The top base was known empty, and Steamhammer calculated that only 1 of the remaining bases was a possible origin for the overlord. The enemy base has been located, so the scout drone doesn’t need to look for it but can get back to mining.

The scout overlord of course wants to see what is in the enemy base. Check its path: At the same moment that the drone turned around, the overlord changed direction from the actual enemy base toward the empty bottom base. Steamhammer drew the wrong conclusion from the enemy overlord’s position. Somehow the “can this overlord have gotten from A to B by this time?” calculation ruled out the actual base A that the overlord came from to reach point B. A minute later, Steamhammer’s zerglings also aimed for the empty base, leaving its own base defenseless.

While this nonsense was going on, Bryan Weber skipped out on a chance to win over breakfast, then a chance to win over lunch, then a chance to win over dinner. It wasn’t hungry at all and chose to wait around instead. Steamhammer won the game despite a build order disadvantage and a scouting bug because the opponent played worse.

Why are there so many bugs? The overlord position inference worked (or correctly drew no inference) in every test I threw at it.