Starcraft AI blog

When I announced that Steamhammer 3.0 would be next, I forgot a step: I want to upgrade to BWAPI 4.4.o. I actually want to make a 2.3.1 release first with the upgrade. I think I can probably do it this month, along with other additions, even though I may not start the work until next week.

Just now I don’t feel like any serious work, so I started to implement queens. Queens are not essential; you can be a great zerg and never spawn one. Often enough, queens are not useful at all. But queens are fun, and I feel like doing fun stuff.

I’m starting with parasite, and I’m thinking the order should be parasite, then infest command center (you get both of these with no research), then ensnare, then broodling. I don’t expect to do them all at first, but I will eventually.

My initial plan is to always make 1 queen versus terran, if the situation permits, in hopes of infesting a command center. And to make 1 queen against protoss if Steamhammer spots juicy parasite bait, like a carrier. In ZvZ a queen is too expensive, unless maybe you can broodling defilers and ultralisks if the game goes that late.

In the longer run, I want Steamhammer to learn for itself which tactics work, and which work against each individual opponent. It should be possible to measure whether parasite brought in information, whether ensnare harmed the opponent, and so on, and estimate whether the queen and the research to use it paid dividends. Decisions based on data are better decisions.

parasite

Parasite is rare in pro games, though it has been used. If you have queens at all there is usually a better use for their energy. But bots are not as knowledgeable as pro players. Could parasite be useful?

I am going to try parasiting flying critters, on maps that have them, to see if it’s useful. And I’ll try parasiting expensive enemy units: Science vessels, battlecruisers, carriers, arbiters. I expect that a few strong terrans will react well, and the bulk of bots will not notice the parasite and will give Steamhammer free information. But we’ll see!

By the way, parasiting a science vessel is not too dangerous if done carefully. Irradiate has a range of 9 tiles, while a queen has vision range 10 tiles, so a queen that approaches cautiously has good chances to launch a parasite without getting irradiated. Parasite has range of 12 tiles (the same as the range of a sieged tank), so if other units spot for the queen then parasite can be always safe.

How to react? If you spot a parasited neutral unit (and it’s not your parasite), kill it. If you’re terran and one of your units gets parasited, you can research restore for medics and remove the parasite. That will take time, though (unless you’re Krasi0, which researches restore pre-emptively and cures spell effects in moments). Zerg has 2 ways to remove parasite (if it ever happens, which is unlikely in ZvZ), both with limited use: 1. If a drone is parasited, you can turn it into a building. 2. If you have a queen of your own, you can place your own parasite on your unit, which overrides the enemy parasite. Protoss doesn’t have any options, and can only be rid of the parasite by killing its own unit.

You can also move a parasited unit away from your army, or use it to show the enemy what you want the enemy to see. The opposite approach is to put it in the front of your forces, so it is the first to be killed.

infest command center

What’s to say? If you bought the queen already and you can infest a command center, you should! For now, I won’t bother with infested terrans, or with details like stopping the attack when the command center falls below half HP so that it is not destroyed before the queen can infest it. Leaving the infested command center where it is may slow the enemy from retaking the base.

ensnare

Ensnare is useful against fast units in groups. I’ll try it first against marines, wraiths, and corsairs. Vultures are hard to tag, but I might experiment. It’s also useful to reveal cloaked units, so it may also be worth researching against dark templar, arbiters, and maybe ghosts.

An ensnared unit moves much more slowly (usually at half speed), and most unit types also shoot a little more slowly. It will be difficult to retreat, or to complete any other tactical maneuver. A logical reaction is to hold your ground until the green goo wears off; you lost a lot of mobility and only a little firepower, so rely on firepower.

broodling

Broodling is expensive to cast; it costs 150 energy, which takes a long time to build up. It’s also the only queen ability that can justify making more than a few queens. It’s good against expensive ground units like tanks and high templar—provided you keep the queens alive so they can do it again (the 100+100 cost of a queen plus the cost of the time to build energy is worth more than one 150+100 tank). Broodling is most valuable in the very late game, when the map is mined out; at that point you want to favor spellcasters no matter your race, because you won’t have the resources to replace units.

There are 2 counters to broodling: 1. Kill the queens. 2. Make units that cannot be broodlinged (wraiths, reavers, archons), or are not worth the cost of broodling (marines).