godot-state-machine-advanced

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Expert blueprint for hierarchical finite state machines (HSM) and pushdown automata for complex AI/character behaviors. Covers state stacks, sub-states, transition validation, and state context passing. Use when basic FSMs are insufficient OR implementing layered AI. Keywords state machine, HSM, hierarchical, pushdown automata, state stack, FSM, AI behavior.

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Sourcethedivergentai/gd-agentic-skills

Added on2026-02-10

NPX Install

npx skill4agent add thedivergentai/gd-agentic-skills godot-state-machine-advanced

SKILL.md Content

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Advanced State Machines

Hierarchical states, state stacks, and context passing define complex behavior management.

Available Scripts

hsm_logic_state.gd

Expert HSM base class with state stack management and validation.

pushdown_automaton.gd

Stack-based state machine for interrupt-resume behavior (pause menus, cutscenes).

MANDATORY: Read hsm_logic_state.gd before implementing hierarchical AI behaviors.

NEVER Do in Advanced State Machines

NEVER forget to call exit() before enter() — Transition without exit? Previous state cleanup skipped = resource leaks (timers, tweens). ALWAYS exit → enter.
NEVER use push_state() without pop_state() — Pushed 100 interrupt states? Stack overflow + memory leak. EVERY push needs matching pop.
NEVER modify state during transition —
```
transition_to()
```
called inside
```
exit()
```
? Re-entrant transition = undefined behavior. Flag transitions, execute after current completes.
NEVER skip state validation —
```
transition_to("AttackState")
```
but state doesn't exist? Silent failure OR crash. Validate state exists before transition.
NEVER forget to process child states — Hierarchical state with sub-states? Parent
```
update()
```
must call
```
current_child_state.update()
```
for delegation.
NEVER use string state names in code —
```
transition_to("Idel")
```
typo = silent failure. Use constants OR enums:
```
transition_to(States.IDLE)
```
.

gdscript

# hierarchical_state.gd
class_name HierarchicalState
extends Node

signal transitioned(from_state: String, to_state: String)

var current_state: Node
var state_stack: Array[Node] = []

func  _ready() -> void:
    for child in get_children():
        child.state_machine = self
    
    if get_child_count() > 0:
        current_state = get_child(0)
        current_state.enter()

func transition_to(state_name: String) -> void:
    if not has_node(state_name):
        return
    
    var new_state := get_node(state_name)
    
    if current_state:
        current_state.exit()
    
    transitioned.emit(current_state.name if current_state else "", state_name)
    current_state = new_state
    current_state.enter()

func push_state(state_name: String) -> void:
    if current_state:
        state_stack.append(current_state)
        current_state.exit()
    
    transition_to(state_name)

func pop_state() -> void:
    if state_stack.is_empty():
        return
    
    var previous_state := state_stack.pop_back()
    transition_to(previous_state.name)

State Base Class