Starcraft AI blog

Tscmoo zerg uses defilers and casts dark swarm, one of few bots with the skill. And... it’s clumsy at it. The swarms usually end up in unhelpful places, or overlap wastefully. Well, Steamhammer can’t place swarms either. The skill is extremely difficult for bots, for 2 related reasons.

One reason is that dark swarm is a coordination skill, and bots suck at coordinating their armies. For an attack, the defiler has to be charged up and in position as the attackers move forward, and place its swarms not only in the right places, but also at the right times, to neutralize as much enemy fire as possible. To do it well, you have to plan or predict how the fight will go, and set up the pieces in good locations ahead of time. One way would be with an abstract combat simulator or planner that could accurately foresee the general movements without working out the details—quite different from today’s concrete combat simulators that inaccurately foresee the details of the fight. Another way would be a large learning system that would be time-consuming to train. I don’t think any current bot has either.

The other reason is that dark swarm is a tactical analysis skill. Suppose you spot a group of marines in the middle of the map. You can’t simply drop a swarm on them and mop them up; if the enemy is any good, the marines will step aside. As long as you have zerglings around, the marines had better stay out of the swarm, but you can only swarm a small portion of the map. Or suppose carriers find your hydras, and you don’t have enough hydras to win, so you lay a swarm over them. Good, the hydralisks are safe, but the carriers can fly away and attack somewhere else. Dark swarm doesn’t protect buildings.

To do it right, the bot has to analyze the tactical situation. If you’re defending a narrow space from marines, great: Swarm the choke, put some lurkers under the ground, and you’re cool until swarm wears off or everything gets irradiated. If there’s more room, then you need to analyze possible maneuvers. If I swarm here, the marines can back up or go around. If they back up, are they farther away from where they want to go, or closer? If they go around, can I trap them? Will the defiler be safe, or is there a risk that this will be my last swarm until I can get another defiler over here? Strong play is super complex.

It just so happens—I’m sure it’s a coincidence—that I am planning to write a tactics analyzer next. Maybe that will help.