Godot notifications

Every Object in Godot implements a _notification method. Its purpose is to allow the Object to respond to a variety of engine-level callbacks that may relate to it. For example, if the engine tells a CanvasItem to "draw", it will call _notification(NOTIFICATION_DRAW).

Some of these notifications, like draw, are useful to override in scripts. So much so that Godot exposes many of them with dedicated functions:

  • _ready(): NOTIFICATION_READY

  • _enter_tree(): NOTIFICATION_ENTER_TREE

  • _exit_tree(): NOTIFICATION_EXIT_TREE

  • _process(delta): NOTIFICATION_PROCESS

  • _physics_process(delta): NOTIFICATION_PHYSICS_PROCESS

  • _draw(): NOTIFICATION_DRAW

What users might not realize is that notifications exist for types other than Node alone, for example:

And many of the callbacks that do exist in Nodes don't have any dedicated methods, but are still quite useful.

One can access all these custom notifications from the universal _notification() method.

Note

Methods in the documentation labeled as "virtual" are also intended to be overridden by scripts.

A classic example is the _init method in Object. While it has no NOTIFICATION_* equivalent, the engine still calls the method. Most languages (except C#) rely on it as a constructor.

So, in which situation should one use each of these notifications or virtual functions?

_process vs. _physics_process vs. *_input

Use _process() when one needs a framerate-dependent delta time between frames. If code that updates object data needs to update as often as possible, this is the right place. Recurring logic checks and data caching often execute here, but it comes down to the frequency at which one needs the evaluations to update. If they don't need to execute every frame, then implementing a Timer-timeout loop is another option.

# Allows for recurring operations that don't trigger script logic
# every frame (or even every fixed frame).
func _ready():
    var timer = Timer.new()
    timer.autostart = true
    timer.wait_time = 0.5
    add_child(timer)
    timer.timeout.connect(func():
        print("This block runs every 0.5 seconds")
    )

Use _physics_process() when one needs a framerate-independent delta time between frames. If code needs consistent updates over time, regardless of how fast or slow time advances, this is the right place. Recurring kinematic and object transform operations should execute here.

While it is possible, to achieve the best performance, one should avoid making input checks during these callbacks. _process() and _physics_process() will trigger at every opportunity (they do not "rest" by default). In contrast, *_input() callbacks will trigger only on frames in which the engine has actually detected the input.

One can check for input actions within the input callbacks just the same. If one wants to use delta time, one can fetch it from the related delta time methods as needed.

# Called every frame, even when the engine detects no input.
func _process(delta):
    if Input.is_action_just_pressed("ui_select"):
        print(delta)

# Called during every input event.
func _unhandled_input(event):
    match event.get_class():
        "InputEventKey":
            if Input.is_action_just_pressed("ui_accept"):
                print(get_process_delta_time())