Starcraft AI blog

After defilers, I did smaller micro and tactics fixes, corrected a few openings, and made other quick improvements. Then I looked over my to-do list and marked the items that would benefit from having on hand the results of a tactical analysis—wow, that’s quite a few, tactics are next! So far I have implemented clustering as mentioned here. I think that within a few days I should be getting practical results like decisions on which direction to retreat in, and then I’ll start seeing where my tactics plan needs revisions.

spider mines

In the meantime, I am also thinking about spider mines. In spider mine placement I wrote about the complicated considerations behind laying mines. Coping with the enemy’s mines is also complicated. These 5 counters to spider mines are all common in pro games.

1. Sweep the mines. The most obvious counter is to bring a detector and ranged units to safely clear the mines.

2. Force the mines. With good micro and the right choice of units, you can try to get by without a detector: You can shoot down spider mines after they pop up. It’s the most common way for terrans to cross a minefield. Dragoons and hydralisks can do it too, with more care, and so can dark templar, or zealots with high enough attack upgrade (+2 for 20 damage, enough to kill a mine in one hit), or in fact any combination of units which are quick and coordinated enough to do the damage in time. One risk that too many mines will pop up at the same time, and you’ll have to dodge them to reduce the damage. Another risk is that the enemy may appear, possibly forcing you back since you won’t be able to cope with mines and enemy units at once.

3. Dodge the mines. Find out which unit of yours the mine is targeting (the mine’s getOrderTarget() will tell you, as Purple Dan pointed out). Simply move the target unit away from the mine—and ideally away from any other units of yours which might be in splash damage range. There is a delay between when the mine decides to stop and explode and when the explosion occurs, and if you are moving away during that delay then you can suffer only splash damage instead of the full effect. (The same idea works for scarabs.) It makes a big difference.

4. Sacrifice to clear the mines. If you want to attack through a minefield, or if you are otherwise in a big hurry to destroy the mines, you won’t be able to do any of the above counters. Send a few zealots or zerglings through the minefield on move command, to trigger as many mines as possible. Being on move command is important; a unit that fires on a mine will stop moving and won’t trigger as many mines. The mine clearing units will be lost, but attackers can follow behind. I’ve occasionally seen terrans sacrifice marines to clear mines, but it is not as common or as effective. This technique is probably worth using during an attack when there is any suspicion of a minefield.

5. Drag the mines. If you are sacrificing a unit on move command to clear mines, what is the best place for your unit to end up? Right next to the enemy, making the enemy’s weapon backfire. A great mine drag can blow up a mass of tanks in moments. Pros know to place spider mines away from where their units intend to go, and to destroy their own mines when their units go there anyway. Bots tend to be careless about mine placement, and are acutely vulnerable to mine drags. Zealots from a shuttle can drag mines too; I think that variation is most valuable when you already know where the mines are.

Less common counters to spider mines exist. You can clear mines without damage by dropping units from a transport and picking them up again with exact timing. Psionic storm will clear mines from an area, but is generally not worth it. Disruption web stops mines from triggering, a use that I have never seen.

One other idea comes to mind, not a common technique as far as I have seen: Play tricks with the mines. You can deliberately leave mines in place and use them to show the enemy what you want the enemy to see. For example, an observer can spot mines without being seen in turn. Notice some mines and leave them unmolested and seemingly undiscovered. Then, when you need a diversion, send an empty shuttle over the mines and it will look convincingly like a drop (a fun use for hallucinate). Someday bots will be smart enough to be fooled!

Knowing that there are spider mines on the map affects your tactical planning from the beginning. Even units like workers that don’t trigger mines will be seen by them, giving away information. Some mines you may spot ahead of time; some you will not. If you’re smart, maybe you can guess where mines are likely. No matter what, you know that moving around the map will rely on the 5 counters.

I would like to get all 5 into Steamhammer for AIIDE, but I’m not sure how much progress I’ll make. I guess mine dodging will be first, since it is so similar to scarab dodging that it can probably be done at the same time.