Starcraft AI blog

I’ve been thinking about mine placement. Where do you lay spider mines? It’s a tiny part of Starcraft, but even by itself it’s super complicated.

Attack units or see the map? IceBot lays mines in a wide grid pattern, each mine in sight range of its neighbors, that gives plenty of warning of incoming attacks or drops. But the mine grid doesn’t kill many units. WOPR lays mines in dense bunches along the shortest path between main bases. Bunched mines don’t scout as widely but are dangerous to force because they trigger in groups. Tyr lays mines in a tighter grid pattern, which could be a compromise between the two goals.

Offensive or defensive placement? IceBot and Tyr lay mines outside their own base to defend. Iron lays mines aggressively outside the opponent’s base as part of a containment game plan. Another good offensive mine placement is up ramps, taking advantage of high ground and vision. I haven’t seen any bots seem to do that intentionally.

Strategic versus tactical area denial. Iron’s containment mines are laid for a strategic purpose. “If you ever want to leave, you have to pass my minefield.” It’s also possible to lay mines for short-term tactical purposes: to block a retreat, to hinder reinforcements, to keep vultures unmolested for a short time while they massacre workers.

Strategic/tactical versus combat mine use. IceBot, WOPR, and Tyr lay mines to be triggered later. Tscmoo and Iron not only do that, but also attack sieged tanks by laying mines next to them that trigger immediately. In human play it’s popular to attack dragoons with mines, but that attack is trickier to pull off because the vultures have to coordinate to block the dragoons from running away.

Blocking an expansion. Several bots, including IceBot and Krasi0, lay mines at expansions. The mine scouts the expansion and delays the opponent from taking it. (By the way, dark templar or burrowed zerglings could do the same.) In principle, mines could block other buildings, but what other opponent building appears in a predictable place? Well, you could use mines to delay terran add-ons.

Luring is still too fancy for bots, but they’ll get there someday. For example, lay a mine in the enemy probe line and then try to entice a zealot in. Devastating when it works.

Mines can also be used to bypass map obstacles, to attack drones when triggered by a larva, and more. Besides the positive uses, a complication is that mines can harm friendly units, which the opponent may try to exploit by mine dragging. Skynet knows how to drag mines (at least its code says it does).

How will PerfectBot lay mines? Being perfect and all, PerfectBot knows the uses of mines and can judge which uses are more important when. I have to imagine that PerfectBot does all the things I mentioned above, and probably in an unpredictable adaptive way. I can’t wait until the end of time to see what it looks like!