Starcraft AI blog

Some bots are so single-minded that they never make air defense of any kind, no hydralisks or spore colonies but only zerglings, no cannons or dragoons but only zealots. Black Crow is a zerg example, and protoss Carsten Nielsen has the same mindset. Theoretically a terran might make only vultures and tanks, though I can’t think of one that doesn’t also make marines or turrets.

Strong bots can cope, of course. But for a lower ranked bot, such an aggressive enemy strategy can be tough to survive. It calls for solid skills that take time to develop. If you prefer a different route, then instead of countering with skill, it’s possible to counter with strategy. Here is a trick counter-strategy for terran:

1. Make a wraith. Well, make as many as you can afford, but 1 should be enough to win. The enemy cannot shoot up, so your wraith is immortal.

2. Lift off any building. Your floating building is immortal, so you cannot lose by having all your buildings destroyed. If you like, you can wait until the building comes under attack.

3. It is still possible to lose on points if you do not finish off the enemy in time, so there is one more step: Use your wraith effectively. Kill overlords and workers to prevent the opponent from constructing buildings faster than you can destroy them. Then slowly take out buildings one at a time. Don’t waste a moment shooting at zerglings or zealots. You don’t need to defend yourself, because you are immortal.

The plan does not automatically work against fast rushes, because you may not get far enough to make a wraith. Possible advanced skill: If you finish the starport but can’t finish a wraith in time, you may be able to lift off the starport and float it to a location that the enemy can’t reach or won’t easily find. And of course you have to decide which opponents to try it against; that might be the hardest part for a low-level bot (and it’s not hard).

Protoss or zerg can play a similar plan on many maps, though it is slower and requires more skills, including analysis of the map. For protoss, make a stargate and a scout as your immortal air unit. To avoid losing, get a robotics facility and shuttle, carry a probe to some place which is buildable and inaccessible by ground—an island or plateau—and make a pylon there. For zerg, you can slow drop a drone on an island base if one is available, and make an extractor, or save up money if the map has an inaccessible space big enough for a hatchery.

One of my ambitions is for Steamhammer to eventually invent this strategy on its own. Steamhammer doesn’t need to be able to reason out that the plan cannot lose; it is enough to recognize the enemy’s habits and come up with logical counters. Step 2 is, “uh oh, the command center is under attack by zerglings, I have to lift it.” Step 1 is not much harder, “here are the units this opponent has made in the past, and based on this history, I could go air.” It doesn’t have to notice that the enemy never gets anti-air, only that going air is a good choice. Step 3 seems to be the hard part.