godot-best-practices

# Godot 4.x GDScript Best Practices

Guide AI agents in writing high-quality GDScript code for Godot 4.x. This skill provides coding standards, architecture patterns, and templates for game development.

## When to Use This Skill

Use this skill when:
- Generating new GDScript code
- Creating or organizing Godot scenes
- Designing game architecture and node hierarchies
- Implementing state machines, object pools, or save systems
- Answering questions about GDScript patterns or Godot conventions
- Reviewing GDScript code for quality issues

Do NOT use this skill when:
- Working with C# in Godot (use C# patterns)
- Working with Godot 3.x (syntax differs significantly)
- Using GDExtension/C++ (different paradigm)
- Working with Godot's visual scripting

## Core Principles

### 1. Naming Conventions

Follow GDScript naming standards consistently:

```gdscript
# Classes: PascalCase
class_name PlayerController
extends CharacterBody2D

# Signals: past_tense_snake_case (describe what happened)
signal health_changed(new_health: int)
signal player_died
signal item_collected(item: Item)

# Constants: SCREAMING_SNAKE_CASE
const MAX_SPEED: float = 200.0
const JUMP_FORCE: int = -400

# Variables and functions: snake_case
var current_health: int = 100
var _private_variable: float = 0.0  # Leading underscore for private

func calculate_damage(base: int, multiplier: float) -> int:
    return int(base * multiplier)

func _private_helper() -> void:  # Leading underscore for private
    pass
```

### 2. Type Hints (Static Typing)

Use explicit type hints everywhere for autocomplete and error detection:

```gdscript
# Variable declarations
var speed: float = 100.0
var player: CharacterBody2D
var items: Array[Item] = []
var stats: Dictionary = {}

# Function signatures with return types
func get_damage() -> int:
    return _base_damage * _multiplier

func find_nearest_enemy(position: Vector2) -> Enemy:
    # Implementation
    return null

# Typed signals (Godot 4.x)
signal score_updated(new_score: int, old_score: int)
signal target_acquired(target: Node2D, distance: float)

# Node references with types
@onready var sprite: Sprite2D = $Sprite2D
@onready var collision: CollisionShape2D = $CollisionShape2D
@onready var animation_player: AnimationPlayer = %AnimationPlayer
```

### 3. Node References

Use modern patterns for stable, refactor-friendly references:

```gdscript
# PREFER: @onready with type hints
@onready var health_bar: ProgressBar = $UI/HealthBar
@onready var weapon: Weapon = $WeaponMount/Weapon

# PREFER: Unique names with % for critical nodes
@onready var player: Player = %Player
@onready var game_manager: GameManager = %GameManager

# AVOID: get_node() in _ready()
func _ready() -> void:
    # Don't do this
    var sprite = get_node("Sprite2D")

# AVOID: Deep fragile paths
@onready var thing = $Parent/Child/GrandChild/GreatGrandChild  # Fragile
```

### 4. Signal-Driven Architecture

Use signals for decoupled communication. Follow "signal up, call down":

```gdscript
# Child node emits signals (doesn't know about parent)
class_name HealthComponent
extends Node

signal health_changed(current: int, maximum: int)
signal died

var _health: int = 100
var _max_health: int = 100

func take_damage(amount: int) -> void:
    _health = max(0, _health - amount)
    health_changed.emit(_health, _max_health)
    if _health <= 0:
        died.emit()
```

```gdscript
# Parent connects to child signals (knows about children)
class_name Player
extends CharacterBody2D

@onready var health: HealthComponent = $HealthComponent
@onready var sprite: Sprite2D = $Sprite2D

func _ready() -> void:
    health.health_changed.connect(_on_health_changed)
    health.died.connect(_on_died)

func _on_health_changed(current: int, maximum: int) -> void:
    # Update UI, play effects, etc.
    pass

func _on_died() -> void:
    sprite.modulate = Color.RED
    queue_free()
```

### 5. Resource Loading

Choose the right loading strategy:

```gdscript
# preload(): Compile-time loading for critical/small assets
const BULLET_SCENE: PackedScene = preload("res://scenes/bullet.tscn")
const PLAYER_SPRITE: Texture2D = preload("res://sprites/player.png")
const DAMAGE_SOUND: AudioStream = preload("res://audio/damage.wav")

# load(): Runtime loading for optional/large assets
func load_level(level_name: String) -> void:
    var path := "res://levels/%s.tscn" % level_name
    var level_scene: PackedScene = load(path)
    var level := level_scene.instantiate()
    add_child(level)

# ResourceLoader for async loading (prevents stuttering)
func _load_level_async(path: String) -> void:
    ResourceLoader.load_threaded_request(path)
    # Check with: ResourceLoader.load_threaded_get_status(path)
    # Get with: ResourceLoader.load_threaded_get(path)
```

## Quick Reference

| Category | Prefer | Avoid |
|----------|--------|-------|
| Node references | `@onready var x: Type = $Path` | `get_node()` in `_ready()` |
| Unique nodes | `%UniqueName` | Deep paths `$A/B/C/D` |
| Resource loading | `preload()` for small/critical | `load()` everywhere |
| Signals | Typed: `signal x(val: int)` | String: `emit_signal("x")` |
| Type safety | Explicit type hints | Untyped variables |
| Constants | `const` or `@export` | Magic numbers/strings |
| Null checks | `is_instance_valid(node)` | `node != null` for freed nodes |
| Coroutines | `await` | `yield` (deprecated) |
| Groups | Scene-specific groups | Global groups for everything |
| Autoloads | Services/managers only | Game logic in autoloads |
| Properties | Setters/getters | Direct mutation |
| Communication | Signal up, call down | Child calling parent methods |

## Code Generation Guidelines

### Script Structure

Order sections consistently:

```gdscript
class_name MyClass
extends Node2D
## Brief description of this class.
##
## Longer description if needed, explaining purpose and usage.

# === Signals ===
signal state_changed(new_state: State)

# === Enums ===
enum State { IDLE, RUNNING, JUMPING }

# === Exports ===
@export var speed: float = 100.0
@export_group("Combat")
@export var damage: int = 10
@export var attack_range: float = 50.0

# === Constants ===
const MAX_HEALTH: int = 100

# === Public Variables ===
var current_state: State = State.IDLE

# === Private Variables ===
var _internal_counter: int = 0

# === Onready ===
@onready var sprite: Sprite2D = $Sprite2D
@onready var collision: CollisionShape2D = $CollisionShape2D

# === Lifecycle Methods ===
func _ready() -> void:
    pass

func _process(delta: float) -> void:
    pass

func _physics_process(delta: float) -> void:
    pass

# === Public Methods ===
func take_damage(amount: int) -> void:
    pass

# === Private Methods ===
func _calculate_knockback() -> Vector2:
    return Vector2.ZERO
```

### Export Annotations

Use exports for editor-configurable values:

```gdscript
# Basic exports
@export var health: int = 100
@export var speed: float = 200.0
@export var player_name: String = "Player"

# Range constraints
@export_range(0, 100) var percentage: int = 50
@export_range(0.0, 1.0, 0.1) var volume: float = 0.8

# Resource exports
@export var texture: Texture2D
@export var scene: PackedScene
@export var audio: AudioStream

# Grouped exports
@export_group("Movement")
@export var walk_speed: float = 100.0
@export var run_speed: float = 200.0

@export_group("Combat")
@export var attack_damage: int = 10

# Enum exports
@export var difficulty: Difficulty = Difficulty.NORMAL
enum Difficulty { EASY, NORMAL, HARD }

# Flags (multiselect)
@export_flags("Fire", "Water", "Earth", "Air") var elements: int = 0
```

## Common Game Patterns

### State Machine (Overview)

Use enum-based state machines for simple cases:

```gdscript
enum State { IDLE, WALK, JUMP, ATTACK }

var current_state: State = State.IDLE

func _physics_process(delta: float) -> void:
    match current_state:
        State.IDLE:
            _process_idle(delta)
        State.WALK:
            _process_walk(delta)
        State.JUMP:
            _process_jump(delta)
        State.ATTACK:
            _process_attack(delta)

func change_state(new_state: State) -> void:
    if current_state == new_state:
        return
    _exit_state(current_state)
    current_state = new_state
    _enter_state(new_state)
```

See `references/patterns/state-machine.md` for advanced implementations.

### Object Pooling (Overview)

Reuse objects to avoid instantiation cost:

```gdscript
class_name ObjectPool
extends Node

var _pool: Array[Node] = []
var _scene: PackedScene

func _init(scene: PackedScene, initial_size: int = 10) -> void:
    _scene = scene
    for i in initial_size:
        var obj := _scene.instantiate()
        obj.set_process(false)
        _pool.append(obj)

func acquire() -> Node:
    if _pool.is_empty():
        return _scene.instantiate()
    var obj := _pool.pop_back()
    obj.set_process(true)
    return obj

func release(obj: Node) -> void:
    obj.set_process(false)
    _pool.append(obj)
```

See `references/patterns/object-pooling.md` for complete implementation.

### Save/Load (Overview)

Use Resources or JSON for save data:

```gdscript
# Custom Resource for save data
class_name SaveData
extends Resource

@export var player_position: Vector2
@export var player_health: int
@export var inventory: Array[String]
@export var level_name: String

# Save
func save_game(data: SaveData) -> void:
    ResourceSaver.save(data, "user://save.tres")

# Load
func load_game() -> SaveData:
    if ResourceLoader.exists("user://save.tres"):
        return load("user://save.tres") as SaveData
    return SaveData.new()
```

See `references/patterns/save-load-system.md` for comprehensive guide.

## Common Anti-Patterns

| Anti-Pattern | Problem | Solution |
|--------------|---------|----------|
| Polling in `_process` | Wastes CPU on unchanged state | Use signals for state changes |
| `get_parent().get_parent()` | Tight coupling, fragile | Signal up, or use groups |
| Deep node paths `$A/B/C/D` | Breaks on refactor | Use `%UniqueName` |
| `load()` in `_process` | Stuttering, memory churn | `preload()` or cache reference |
| String signals `emit_signal("x")` | Typos, no autocomplete | Typed: `signal_name.emit()` |
| Untyped `@onready var x = $Node` | Loses autocomplete | Always add type hint |
| Logic in autoloads | Testing difficulty, coupling | Keep autoloads thin |
| Magic numbers | Unclear meaning | Use `const` or `@export` |
| `node != null` for freed nodes | Returns true for freed | Use `is_instance_valid()` |
| Circular dependencies | Load errors, unclear flow | Dependency injection or signals |

## Additional Resources

### Pattern Guides
- `references/patterns/state-machine.md` - Full state machine implementations
- `references/patterns/object-pooling.md` - Complete pooling system
- `references/patterns/save-load-system.md` - Comprehensive save/load guide
- `references/patterns/input-handling.md` - Input buffering and rebinding

### Architecture
- `references/architecture/project-structure.md` - Directory organization
- `references/architecture/scene-composition.md` - Scene design patterns
- `references/architecture/node-communication.md` - Signals vs direct calls

### GDScript Deep Dives
- `references/gdscript/type-system.md` - Static typing in depth
- `references/gdscript/coroutines-await.md` - Async patterns with await

### Templates
- `assets/templates/base-script.gd.md` - Standard script template
- `assets/templates/state-machine.gd.md` - State machine template
- `assets/templates/autoload-manager.gd.md` - Autoload singleton template

## Limitations

- GDScript only (not C#, GDExtension, or VisualScript)
- Godot 4.x syntax (some patterns differ from 3.x)
- Game-focused patterns (not editor plugin development)
- No runtime validation scripts (GDScript requires Godot runtime)