Starcraft AI blog

That’s enough data analysis for now. Too much of the same is growing stale. I still want to dig deeper into the SSCAIT data set, but first let’s take a break for a few of my usual ill-founded suggestions. Today a rant: Bots are inefficient at destroying bases.

Here’s a hidden principle that is implicit in Starcraft strategy and only occasionally mentioned: Who wins the base race? If the two armies bypass each other and each races to finish off the enemy base, who wins the game?

I think human players over some low level can answer this question off the cuff in common situations, because it’s basic to decision making. If you can win the base race, then you are free to leave the path to your base open. You have freedom of maneuver and can engage or not as you choose. You can consider whether it’s smart to work your way behind the enemy army. If you are fated to lose the base race, then you have no choice but to engage the enemy to avoid losing. When you are under threat, all you can do is seek favorable ground to make your stand. You are on the strategic defensive, in a sense. You’re not necessarily on the tactical defensive—for example, active forward play like Iron’s blocks the path to Iron’s bases and prevents any base race as long as it stands, and tactically it is aggressive not defensive.

Whether you can win a pure elimination race is only one consideration, of course. Nothing is ever that simple! The more mobile army has more choices. Mutalisks may be fast enough to ravage the enemy workers and still return in time to help defend, especially if the air distance is less than the ground distance. Even in that case, estimating the base race is how you tell when it’s time to return.

For an experienced human it’s easy to know who has the advantage in the base race, but it seems tricky for bots. Zerg has fewer buildings but they’re likely to be split between more bases. Killing a base includes defeating reinforcements produced during the process. The stronger army doesn’t necessarily win the base race; it depends on the situation. A hydra army that loses to the terran infantry army might win the base race because of higher damage rate since medics don’t shoot, but a lurker-ling army that wallops the marines could lose the base race because terran will float buildings while trashing the zerg bases. If it’s close, both sides may try to live longer with hidden buildings, a distant extractor for zerg or a sneak pylon for protoss.

And, of course, bots are not too efficient at killing bases and not too clever with survival tricks.

MassCraft’s tactical search understands base races in principle. I’m not sure whether it’s accurate enough to understand them in practice.

A bot that—one way or another—understood base races and could instigate them at the right times would probably score occasional easy wins. But I expect that the main advantage would be as for humans, knowledge of when you are free to maneuver and when you are forced to engage.

Lesson: If you take away nothing else, take away the idea that rapidly finishing off an undefended base has value. A lot of bots are slow and lazy about it, I guess because it’s “not important.” In reality, even if you’re attacking an undefended expansion and not caught in an elimination race, it’s important to target the key buildings first and destroy everything efficiently. First, you don’t know when enemy reinforcements might show up to interrupt. And second, the sooner the better when it comes to freeing your forces for the rest of the fight.