Limboai

LimboAI

> Related skills: ai-navigation for movement the tasks drive, state-machine for core-engine FSM (when you don't need an addon), godot-brainstorming for choosing an AI approach.

> Addon: LimboAI · version v1.7.1 · Godot 4.6+ · MIT · source: https://github.com/limbonaut/limboai · written in C++ (GDExtension; engine-module build also available). GDExtension exposes GDScript; C# requires the module build (not GDExtension in v1.7.1).

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1. When to use LimboAI

| Approach | Best for | |---|---| | Core-engine FSM (state-machine skill) | Simple agents, void: # BTPlayer starts executing automatically (active = true by default). # Connect to updated(status) to react when the tree finishes. btplayer.updated.connect(onbtupdated)

func onbtupdated(status: int) -> void: if status == BT.SUCCESS: btplayer.restart() # loop the tree

### C#

```csharp
// EnemyAI.cs
using Godot;

public partial class EnemyAI : CharacterBody2D
{
    [Export] private BTPlayer _btPlayer;

    public override void _Ready()
    {
        _btPlayer.Updated += OnBtUpdated;
    }

    private void OnBtUpdated(int status)
    {
        if (status == (int)BT.Status.Success)
            _btPlayer.Restart();
    }
}

BTPlayer.UpdateMode controls when the tree ticks: IDLE (every _process), PHYSICS (every _physics_process, default), or MANUAL (call bt_player.update(delta) yourself).

---

4. Custom tasks

Subclass BTAction (multi-tick work) or BTCondition (immediate check). Annotate with @tool so _generate_name() and _get_configuration_warnings() work in the editor. Place scripts under res://ai/tasks/; subfolders become task categories.

GDScript

@tool
extends BTAction
## Moves the agent toward a blackboard position each tick.

@export var target_pos_var: StringName = &"target_pos"
@export var speed: float = 200.0

func _generate_name() -> String:
    return "MoveToward %s" % LimboUtility.decorate_var(target_pos_var)

func _setup() -> void:
    pass  # one-time init; agent and blackboard are available here

func _enter() -> void:
    pass  # called when task transitions from non-RUNNING → RUNNING

func _tick(delta: float) -> Status:
    var target: Vector2 = blackboard.get_var(target_pos_var, Vector2.ZERO)
    if agent.global_position.distance_to(target)  void:
    pass  # cleanup after SUCCESS or FAILURE

@tool
extends BTCondition
## Returns SUCCESS if the agent is within range of a target node.

@export var target_var: StringName = &"target"
@export var distance_max: float = 150.0

var _max_sq: float

func _setup() -> void:
    _max_sq = distance_max * distance_max

func _tick(_delta: float) -> Status:
    var target: Node2D = blackboard.get_var(target_var, null)
    if not is_instance_valid(target):
        return FAILURE
    var in_range := agent.global_position.distance_squared_to(
        target.global_position) 
        $"MoveToward {LimboUtility.DecorateVar(TargetPosVar)}";

    public override void _Setup() { }

    public override void _Enter() { }

    public override Status _Tick(double delta)
    {
        var target = (Vector2)Blackboard.GetVar(TargetPosVar, Vector2.Zero);
        var body = (CharacterBody2D)Agent;
        if (body.GlobalPosition.DistanceTo(target)  _maxSq = DistanceMax * DistanceMax;

    public override Status _Tick(double delta)
    {
        var target = Blackboard.GetVar(TargetVar, default(Variant)).As();
        if (!GodotObject.IsInstanceValid(target))
            return Status.Failure;
        var agent2D = (Node2D)Agent;
        bool inRange = agent2D.GlobalPosition.DistanceSquaredTo(
            target.GlobalPosition)  Status:
    # Read with a default; use no type annotation for object vars
    # to avoid errors if the stored instance was freed.
    var speed: float = blackboard.get_var(speed_var, 100.0)
    var obj = blackboard.get_var(target_var, null)
    if not is_instance_valid(obj):
        return FAILURE

    # Write back
    blackboard.set_var(speed_var, speed * 1.1)
    return RUNNING

C#

// C# has no generic GetVar — cast the returned Variant.
using Godot;

[Tool]
public partial class SampleTask : BTAction
{
    [Export] public StringName SpeedVar { get; set; } = "speed";
    [Export] public StringName TargetVar { get; set; } = "target";

    public override Status _Tick(double delta)
    {
        float speed = (float)Blackboard.GetVar(SpeedVar, 100f);
        var obj = Blackboard.GetVar(TargetVar, default(Variant)).As();
        if (!GodotObject.IsInstanceValid(obj))
            return Status.Failure;

        Blackboard.SetVar(SpeedVar, speed * 1.1f);
        return Status.Running;
    }
}

Useful Blackboard methods: has_var(name), erase_var(name), list_vars(), get_vars_as_dict(), bind_var_to_property(name, obj, prop), link_var(name, target_bb, target_name), print_state() (debug).

BlackboardPlan defines the variable schema (types, defaults, hints) and is edited in the Inspector on BTPlayer or LimboHSM. Call blackboard_plan.create_blackboard(scene_root) to create a scoped Blackboard at runtime.

---

6. Hierarchical state machine (LimboHSM)

LimboHSM is a LimboState node that manages child LimboState nodes. Transitions fire when a state calls dispatch(event). See [references/hsm.md](references/hsm.md) for advanced patterns (any-state transitions, BTState, nested HSMs, guards).

GDScript — scene-tree setup

# Character.gd — scene tree: Character → LimboHSM → IdleState, MoveState
extends CharacterBody2D

@onready var hsm: LimboHSM = $LimboHSM
@onready var idle: LimboState = $LimboHSM/IdleState
@onready var move: LimboState = $LimboHSM/MoveState

func _ready() -> void:
    hsm.add_transition(idle, move, idle.EVENT_FINISHED)
    hsm.add_transition(move, idle, move.EVENT_FINISHED)
    hsm.initialize(self)
    hsm.set_active(true)

C# — scene-tree setup

// Character.cs
using Godot;

public partial class Character : CharacterBody2D
{
    [Export] private LimboHSM _hsm;
    [Export] private LimboState _idle;
    [Export] private LimboState _move;

    public override void _Ready()
    {
        _hsm.AddTransition(_idle, _move, _idle.EventFinished);
        _hsm.AddTransition(_move, _idle, _move.EventFinished);
        _hsm.Initialize(this);
        _hsm.SetActive(true);
    }
}

GDScript — state script

# IdleState.gd
extends LimboState

func _setup() -> void:
    pass  # agent and blackboard available; runs once during hsm.initialize()

func _enter() -> void:
    agent.get_node("AnimationPlayer").play("idle")

func _exit() -> void:
    pass

func _update(delta: float) -> void:
    if Input.get_vector(&"ui_left", &"ui_right", &"ui_up", &"ui_down").length() > 0.1:
        dispatch(EVENT_FINISHED)

C# — state script

// IdleState.cs
using Godot;

public partial class IdleState : LimboState
{
    public override void _Setup() { }

    public override void _Enter()
    {
        Agent.GetNode("AnimationPlayer").Play("idle");
    }

    public override void _Exit() { }

    public override void _Update(double delta)
    {
        if (Input.GetVector("ui_left", "ui_right", "ui_up", "ui_down").Length() > 0.1f)
            Dispatch(EventFinished);
    }
}

---

Implementation checklist

• [ ] BTPlayer added as a child of the agent; behavior_tree resource assigned
• [ ] Custom tasks annotated with @tool (GDScript) or [Tool] (C#) for editor display
• [ ] Every _tick returns SUCCESS, FAILURE, or RUNNING — never void/null
• [ ] Blackboard keys documented as exported StringName properties (suffix _var)
• [ ] C# Blackboard reads cast the Variant explicitly ((float)Blackboard.GetVar(...))
• [ ] C# uses module build (not GDExtension) for C# support
• [ ] BTPlayer.updated signal used (not deprecated behavior_tree_finished)
• [ ] HSM: all LimboState nodes wired with add_transition before initialize()
• [ ] HSM: set_active(true) called after initialize()
• [ ] HSM transitions are exhaustive — every reachable state has an exit path
• [ ] BBParam inspector binding: use module build; GDExtension lacks the param editor UI

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: jame581
• Source: jame581/GodotPrompter
• License: MIT

Install and usage instructions live in the source repository linked above.