Starcraft AI blog

I’ve uploaded Steamhammer 3.3 to SSCAIT. The changes to play are slight, and stream viewers are unlikely to notice anything even if they look closely. Nevertheless, it’s an important upgrade. If no disasters strike overnight, I should get source up tomorrow.

BWAPI 4.4.0

• Steamhammer is updated to BWAPI 4.4.0, at long last. In AIIDE this year, it was the only updated bot which still relied on the older BWAPI 4.1.2, now Positively Ancient by community consensus.

Part of the change is switching from VS2013 to VS2017. VS2017 has a more capable compiler backend with a stronger optimizer. Steamhammer’s DLL size fell from 1,211,392 bytes for version 3.2.20 to 1,100,800 bytes for 3.3, reflecting the difference in compiler, small changes in Steamhammer’s size, and any changes in the size of BWAPI.lib. That’s about a 9% improvement in object size for the effort of upgrading, surprisingly large. The bot presumably runs faster, but I didn’t measure it. Steamhammer already runs fast, so I doubt any speed improvement matters.

• If the opponent is terran, Steamhammer now tracks enemy comsat scans. Call InformationManager::getEnemyScans() to fetch the current scans. BWAPI 4.4.0 makes enemy scans available, where BWAPI 4.1.2 did not.

errors related to spell units

The spells comsat scan, disruption web, and dark swarm are represented in BWAPI by special units which belong to the player who casts them. Code that looks at units often has to know that. I searched through Steamhammer for code which did not know it, and found cases. Some were due to scans and only had to be fixed because of the 4.4.0 upgrade—it’s a subtlety for authors to be aware of.

• An enemy scan does not imply that the enemy has air tech.

• When deciding how many scourge are needed, don’t count enemy scans as air units.

• In squad targeting, do not target scourge at an enemy scan.

• In micro targeting (which is different from squad targeting), do not target enemy spell units.

• When clearing neutral blocks (like blocking eggs that are part of the map), do not target neutral spell units. A small number of maps have permanent neutral dwebs or swarms.

• In map analysis, don’t mark the areas covered by neutral spells as unwalkable.

• Don’t try to include a spell unit in a squad. I think spell units didn’t get in anyway, but now they are cut off at the first validity check, so it is as safe as can be.

zerg

• Research in a hive. Until 4.4.0, a hive could perform no research due to a BWAPI bug. Steamhammer worked around it by getting all its research done before upgrading to hive, crimping its strategy choices. In hive rush openings, it was unable to research overlord speed ever, a serious issue. I’m so glad this is finally cured.

• Research +3 air upgrades. Until 4.4.0, it was not possible to upgrade in a greater spire due to a BWAPI bug, and Steamhammer had a workaround to avoid +3 spire upgrades altogether.

• Trivial bug fix: If Steamhammer lost its queen’s nest at any time after it started morphing its hive, but did not lose the hive, it was unable to replace the queen’s nest. Well, it rarely needed to, but it does have queen skills. The limitation is lifted.

• Indiscernible bug fix: Prevent a production freeze that could have happened if Steamhammer wanted to research burrow, had no hatchery other than a lair or hive, and the lair or hive was busy researching something else. There was virtually no chance of this bug ever occurring.

openings

• No doubt under the influence of an Infernal Compulsion Engine (old tech now superseded by Electric Motives), I added the zerg openings 9Pool8Hatch and 9Pool9Hatch. Crona plays a related opening with success.