A-Life

A-Life is the NPC simulation logic used in the S.T.A.L.K.E.R. engine.
== Combat AI ==
Refer to Combat tactics for details.
== Unarmed NPCs ==
Unarmed NPCs have quite a chaotic behavior, panicking at the first sight of any enemy; sometimes that can interfere with certain quests. You can sell them any broken gun and one magazine worth of ammo for it, to have them think straight.
== Online range ==
Everything inside the 160m range around the player is considered to be "online", loaded into memory with full AI and physics simulation. Once the entity gets out of that range, it switches "offline", with heavily simplified logic on a 2D grid instead of the 3D space.
In OP-2.2, some NPCs are forcibly excluded from switching, and remain online even past switching distance. This makes long-range sniping missions possible (for example, in one late game mission you'll have to snipe targets across the entire Jupiter).
== Camp backups ==
Once any regular camp gets fully eliminated, it respawns somewhere in the certain location of the Zone, characteristic for these mutants or NPCs (for example Monolithians respawn in Labyrinth, pseudodogs in Forgotten Forest etc), and starts slowly walking back across the entire Zone, crossing transitions between locations, even those you might not have yet.
That's the reason you can sometimes get a squad of 16 Monolithians dumped onto your face in the middle of Yantar. You killed them in Central Pripyat before, they respawned at Labyrinth and transitioned into Yantar, exiting at the road. For the same reason, you can encounter neutral and hostile stalkers or mutants across the entire Zone, walking somewhere.
== Despawning ==
NPC bodies despawn after moving to a different location, provided they don't have any "important" items on them, such as cash, Monolithian ID tags, or quest items. On very rare occasions, the bodies won't despawn at all.
Any body that haven't despawned for several days will decay into a zombie, if not set to be permanent (for example Chemist's body in Forgotten Forest is scripted to not decay).
Empty mutant bodies will despawn once they get beyond the switching distance. Which is a nice way to filter out empty bodies from any carnage - just move 160m away and get back. Sometimes in huge fights, especially Wave of Mutants but also some others, they will despawn much faster even with parts still on them, to not become a hog for the game engine.
Most items dropped onto the ground won't despawn at all, except for broken weapons (condition worse than 50%).
Keep in mind that the engine handles stacked piles of bodies very poorly, with a heavy FPS drop accompanying it.
Category:Core mechanics