soojung-kang/godot-4-migration

Godot 4 Migration Guide

Overview

A critical guide for developers transitioning from Godot 3.x to Godot 4. This skill focuses on the major syntax changes in GDScript 2.0, the new Tween system, and export annotation updates.

When to Use This Skill

• Use when porting a Godot 3 project to Godot 4.
• Use when encountering syntax errors after upgrading.
• Use when replacing deprecated nodes (like Tween node vs create_tween).
• Use when updating export variables to @export annotations.

Key Changes

1. Annotations (@)

Godot 4 uses @ for keywords that modify behavior.

• export var x -> @export var x
• onready var y -> @onready var y
• tool -> @tool (at top of file)

2. Setters and Getters

Properties now define setters/getters inline.

Godot 3:

var health setget set_health, get_health

func set_health(value):
    health = value

Godot 4:

var health: int:
    set(value):
        health = value
        emit_signal("health_changed", health)
    get:
        return health

3. Tween System

The Tween node is deprecated. Use create_tween() in code.

Godot 3:

$Tween.interpolate_property(...)
$Tween.start()

Godot 4:

var tween = create_tween()
tween.tween_property($Sprite, "position", Vector2(100, 100), 1.0)
tween.parallel().tween_property($Sprite, "modulate:a", 0.0, 1.0)

4. Signal Connections

String-based connections are discouraged. Use callables.

Godot 3:

connect("pressed", self, "_on_pressed")

Godot 4:

pressed.connect(_on_pressed)

Examples

Example 1: Typed Arrays

GDScript 2.0 supports typed arrays for better performance and type safety.

# Godot 3
var enemies = []

# Godot 4
var enemies: Array[Node] = []

func _ready():
    for child in get_children():
        if child is Enemy:
            enemies.append(child)

Example 2: Awaiting Signals (Coroutines)

yield is replaced by await.

Godot 3:

yield(get_tree().create_timer(1.0), "timeout")

Godot 4:

await get_tree().create_timer(1.0).timeout

Best Practices

• ✅ Do: Use @export_range, @export_file, etc., for better inspector UI.
• ✅ Do: Type all variables (var x: int) for performance gains in GDScript 2.0.
• ✅ Do: Use super() to call parent methods instead of .function_name().
• ❌ Don't: Use string names for signals (emit_signal("name")) if you can use the signal object (name.emit()).

Troubleshooting

Problem: "Identifier 'Tween' is not a valid type." Solution: Tween is now SceneTreeTween or just an object returned by create_tween(). You rarely type it explicitly, just use var tween = create_tween().