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df7832aa43 Replaced our NPC AI with Behavior Trees. (#96628)
This PR replaces our current NPC AI with a [behavior tree
system](https://en.wikipedia.org/wiki/Behavior_tree_(artificial_intelligence,_robotics_and_control)).
Behavior trees are a common way of creating AI in which you place nodes
in a tree structure to define what actions an AI should take.

AI controllers defined a list of /datum/ai_planning_subtree types in
behavior_nodes. Each subtree was a self-contained unit that could call
queue_behavior() to fire off /datum/ai_behavior actions. The controller
iterated subtrees in order, each one deciding independently whether to
queue something and deciding whether the next subtree would run.

This has a few issues:
1. There's no real structure; you are just defining a list of things to
try in order.
2. There was a loooot of subtrees that were basically the same as
another but with some slight modification
3. It was hard to understand.

Controllers now define a single json file describing a tree of nodes.
The tree is composed of structural composites:

Sequence - do A, then B, then C (and so on)
Selector - try A, if it fails try B, then C (and so on)
Parallel - run A and B simultaneously, with configurable failure/success
policies and or looping behavior
Subplan - loop a child continiously

Along that we also have "Decorators". These are nodes that basically
check a condition (E.g.; do we have a combat target). These decorators
can be used to gate behavior and are re-useable across behavior trees.
They also have a concept known as "Observers". Which lets them cancel
lower priority behavior in case their condition changes (Which we check
whenever a signal fires that fits that specific decorator). This makes
the AI much more responsive to change in environment.

For behaviors, we still use the ai_behavior datums. These are the actual
behaviors such as "Move to X", "Attack X". The only major change is that
these can no longer sleep() since they now run in the ai_controller.

Lastly, we now also have subtrees, except now they are essentially
pieces of behavior tree that can be re-used, or even overriden at
runtime or as a variable. Allowing for making modular AI made out of
several smaller trees.

You can set variables on these nodes directly via the extension (see
below), which should reduce the need to make subtypes of behaviors by a
lot. All of these vars are saved on the JSON and will be applied at
runtime.

If you are using subtrees, you can also assign "bindings" to these
variables, which will allow instances of the subtree to override those
variables.

Since a tree structure with variables becomes hard to parse in a JSON,
I've made a VSCode extension to edit these JSONs:

https://marketplace.visualstudio.com/items?itemName=BehaviorTreeG.behaviortreeg
https://github.com/CabinetOnFire/BehaviorTreeG

<img width="1795" height="1268" alt="image"
src="https://github.com/user-attachments/assets/56aa2f0b-3cf9-449f-bca4-8281fca82db6"
/>

This extension allows you to edit the behavior tree JSONs, and browse
through all the behaviors/decorators/subtrees we have

If you'd like more info on how to build these AI check out the
learn_ai.md. I will also make a tutorial to go over more depth on what
the system offers because I kind of suck at doing technical write-ups.

Targetting has been changed to. I've made a new acquire_targets behavior
that takes a target_source (what am I targetting) and
targetting_strategy (what does the candidate need to fulfill to be
considered a target). This allows us to make composites targetting
combinations to reduce the amount of specific find_and_set esque
behaviors we had before. Not everything is ported to this system but
that would be a longer term goal.

I've added a new build_bt script that converts all the behavior tree
JSONs into compiled versions. Why is this needed? Because I wanted to
keep using defines in behavior trees, so we need a way to convert this
into literal values before we send it to DM. This script runs on compile
and should also run in CI (If I didn't fuck that up!). This saves to a
new build/ folder.

I've ported every single AI in the game to this system (except raptors,
Kobsa is working on those so should be in soon!), so I do expect some
bugs to come out of this. But I also fixed some issues that have
probably been in the game for a long time such as:
- Fixed penguins being unable to fish
- Fixed bileworms not being able to devour people
- Fixes goldgrubs not grubbing gold (they could not mine!)
- Lizards actually eat food they find

Either way, I'd reccomend a long TM on this.

1. (Hopefully) a better development experience for making AI
2. Less copy-paste for behaviors, we should be able to re-use more
pieces to make behavior
3. Behavior trees is a more common pattern in making AI, so it should be
easier to find resources to find out how to do things.

🆑 CabinetOnFire, Iamgoofball, SmartKar, Ben10omintrix
refactor: Replaces our AI system with behavior trees, porting all
datum/ai to it
/🆑

I will add this PR with more details down the line. I think I got the
big picture but its a big PR, so sorry if I missed something important.

---------

Co-authored-by: Iamgoofball <iamgoofball@gmail.com>
Co-authored-by: SmArtKar <44720187+SmArtKar@users.noreply.github.com>
Co-authored-by: Ghom <42542238+Ghommie@users.noreply.github.com>
Co-authored-by: Ben10Omintrix <138636438+Ben10Omintrix@users.noreply.github.com>
Co-authored-by: SyncIt21 <110812394+SyncIt21@users.noreply.github.com>
2026-08-15 10:33:57 -06:00

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//not quite simple animal megafauna but close enough
// port actual megafauna stuff once it gets used for lavaland megafauna
//im using it for stuff both of them get
/mob/living/basic/boss
combat_mode = TRUE
status_flags = NONE
abstract_type = /mob/living/basic/boss
sentience_type = SENTIENCE_BOSS
mob_biotypes = MOB_ORGANIC|MOB_SPECIAL
faction = list(FACTION_MINING, FACTION_BOSS)
damage_coeff = list(BRUTE = 1, BURN = 1, TOX = 0, CLONE = 0, STAMINA = 0, OXY = 0)
obj_damage = 400
unsuitable_cold_damage = 0
unsuitable_heat_damage = 0
unsuitable_atmos_damage = 0
move_force = MOVE_FORCE_OVERPOWERING
move_resist = MOVE_FORCE_OVERPOWERING
pull_force = MOVE_FORCE_OVERPOWERING
mob_size = MOB_SIZE_HUGE
layer = LARGE_MOB_LAYER
flags_1 = PREVENT_CONTENTS_EXPLOSION_1
/// Name for the GPS signal of the megafauna
var/gps_name = null
/// What crusher trophy/trophies this mob drops, if any
/// Should be wrapped in a list for sanity when we pass it to the element.
var/list/crusher_loot = null
/// Loot dropped on death in normal circumstances
var/list/regular_loot = list()
/// What achievements do we give our defeater?
var/list/achievements = null
/// What type of achievement we give for crusher kills, if any.
var/crusher_achievement_type = null
/// What memory to give to victor who have killed us, if any.
var/victor_memory_type = null
/mob/living/basic/boss/Initialize(mapload)
. = ..()
AddElement(/datum/element/wall_tearer, tear_time = 1 SECONDS)
if(gps_name)
AddComponent(/datum/component/gps, gps_name)
ADD_TRAIT(src, TRAIT_SPACEWALK, INNATE_TRAIT)
add_traits(list(TRAIT_NO_TELEPORT, TRAIT_MARTIAL_ARTS_IMMUNE, TRAIT_LAVA_IMMUNE, TRAIT_ASHSTORM_IMMUNE, TRAIT_NO_FLOATING_ANIM), MEGAFAUNA_TRAIT)
AddComponent(/datum/component/seethrough_mob)
AddElement(/datum/element/simple_flying)
AddElement(/datum/element/death_drops, string_list(regular_loot))
handle_crusher_loot()
handle_achievements()
/mob/living/basic/boss/gib()
if(health > 0)
return
return ..()
/mob/living/basic/boss/dust(just_ash, drop_items, give_moodlet, force)
if(!force && health > 0)
return
return ..()
/mob/living/basic/boss/death(gibbed)
if (health > 0 && !gibbed) // prevents instakills
return
return ..()
/mob/living/basic/boss/ex_act(severity, target)
switch (severity)
if (EXPLODE_DEVASTATE)
adjust_brute_loss(250)
if (EXPLODE_HEAVY)
adjust_brute_loss(100)
if (EXPLODE_LIGHT)
adjust_brute_loss(50)
return TRUE
/mob/living/basic/boss/early_melee_attack(mob/living/target, list/modifiers, ignore_cooldown)
. = ..()
if(. || !istype(target))
return
if(should_devour(target))
devour(target)
return BASIC_MOB_END_ATTACK_CHAIN_COOLDOWN
return
/// Determines if this mob is worth devouring
/mob/living/basic/boss/proc/should_devour(mob/living/victim)
return victim.stat == DEAD || (victim.health <= HEALTH_THRESHOLD_DEAD && HAS_TRAIT(victim, TRAIT_NODEATH))
/// Devours a target and restores health to the megafauna
/mob/living/basic/boss/proc/devour(mob/living/victim)
if(isnull(victim) || victim.has_status_effect(/datum/status_effect/gutted))
return FALSE
celebrate_kill(victim)
if(!is_station_level(z) || client) //NPC monsters won't heal while on station
heal_overall_damage(victim.maxHealth * 0.5)
victim.investigate_log("has been devoured by [src].", INVESTIGATE_DEATHS)
if(iscarbon(victim))
qdel(victim.get_organ_slot(ORGAN_SLOT_LUNGS))
qdel(victim.get_organ_slot(ORGAN_SLOT_HEART))
qdel(victim.get_organ_slot(ORGAN_SLOT_LIVER))
victim.adjust_brute_loss(500)
victim.death() //make sure they die
victim.apply_status_effect(/datum/status_effect/gutted)
return TRUE
/// Small little taunt when we epically troll someone
/mob/living/basic/boss/proc/celebrate_kill(mob/living/poor_sap)
visible_message(
span_danger("[src] disembowels [poor_sap]!"),
span_userdanger("You feast on [poor_sap]'s organs, restoring your health!"),
)
/// Handles adding all relevant achievements when applicable (probably when we are defeated)
/// Achievements being null/no length is handled in the element itself.
/mob/living/basic/boss/proc/handle_achievements()
if(length(achievements) <= 0)
return
AddElement(/datum/element/kill_achievement, string_list(achievements), crusher_achievement_type, victor_memory_type)
/// Handles adding crusher loot when applicable (probably when we are defeated)
/mob/living/basic/boss/proc/handle_crusher_loot()
if(isnull(crusher_loot))
return
AddElement(\
/datum/element/crusher_loot,\
trophy_type = string_list(crusher_loot),\
guaranteed_drop = 0.6,\
drop_immediately = basic_mob_flags & DEL_ON_DEATH,\
)