Talk:Alien movement patterns
There are quite a few different movement patterns amongst the different aliens. One of the most noticable difference is how they use their elevation. Walking aliens will leave the upper floors of buildings and get onto the ground or roof. Flying aliens will lurk on the upper floor and ambush soldiers later, so you can counter this by removing a wall and exposing the upper floor. Flying aliens are generally more capable with grenades as they have more geometry available to them. There are also blind spots due to elevation when an alien at a higher level can see your soldier while you cannot see them, so make sure your next soldier approaches from a better angle.
Sectoids and reapers run about all over the place. Snakemen seem more willing to wait in ambush. Crysallids will run quickly but then slow down on later turns as they run out of stamina. They are most dangerous after standing still for a few turns in panic, recovering their stamina.
A common point for aliens to stop is outside a farm doorway, especially on the edge of the map. This sometimes hides them behind the door. Always make sure you approach these points with good visibility. Some paddocks can be fully enclosed with fences or walls so expect to see walking aliens trapped in there, even when the surrounding countryside seems safe.
The last alien alive will typically stand still and stop moving. This will make it more dangerous as it doesn't show up on motion scanners and has all its time units left for reaction shots. Cyberdiscs often stop moving for long periods and wait in ambush.
If there are plenty of aliens alive then even the most reluctant will eventually leave safety behind and come looking for soldiers. At times though they can suddenly move out in dangerously large groups which dramatically increases their threat. Keep an eye out for that happening.
I don't feel I've played enough to really be a master on this subject, but I'd like to put out what I know.
First off, aliens are agents in the battlescape that are subject to the constraints put upon them. This is opposed to free-ranging agents that can do anything, but try to simulate what an agent should act like. This means that Julian Gollop and Nick Gollop weren't cheap bastards when making their AI. I'm pretty sure of this as I've never seen aliens "cheat".
Secondly, I believe that most of what Egor has commented on is due to the differences in the different alien stats and abilities. This is emergent behavior rather then being individually programmed that way. IE, I think all the aliens have the same basic AI behind them. Special abilities like that of the floaters, reapers, crysallids, psycic, and the whatnotpods, all probably have their own section of code, but they all follow the basics.
Thirdly, they ignore their friends. I've never seen them coordinate, have you?
So, these basics, what are they? My understanding is that the aliens have three states: Wander, Guard/Rest, and Engage. Yeah, the Engage state would be the "Aggression Formula" mentioned in the article. As far as wandering, each map tile has waypoints or paths described in them so that units can walk around. The edges of tiles have defined crossing points that can act like closed gates if it's the edge of the battlescape or the tiles don't match.
This doesn't sound like that complicated of an AI. So why is X-COM so hard to play? Your units are fragile, and sitting scared in a closet with a bazooka aimed at the door with your finger on the trigger is a good strategy.
Tests I'd like to see but am too lazy to do myself: 1. Test if the last alien will eventually wander, or if it will forever be holed up in it's corner. 2. Is there really a different behaviour for aliens who engage players? See if they ever leave the defined path. 3. Will aliens pass each other when walking between waypoints?
that's all I've got. Heckruler 14:02, 14 February 2007 (PST)