Entering/Exiting the screen

Problem

You want to detect when an object enters or exits the screen.

Solution

The engine provides a node for this: VisibilityNotifier2D. Attach this node to your object, and you’ll be able to use its screen_entered and screen_exited signals.

Example 1

Consider a projectile that travels in a straight line after it’s fired. If we continue firing, eventually we’ll have a large number of objects for the engine to track, event though they’re offscreen, which can cause lag.

Here’s the movement code for the projectile:

extends Area2D

var velocity = Vector2(500, 0)

func _process(delta):
    position += velocity * delta

To have the projectile automatically deleted when it moves offscreen, add a VisibilityNotifier2D and connect its screen_exited signal.

func _on_VisibilityNotifier2D_screen_exited():
    queue_free()

Example 2

We have an enemy that performs some actions, such as moving along a path or playing an animation. On a large map with many enemies, only a few of them will be onscreen at the same time. We can disable the enemy’s actions while it’s offscreen using VisibilityNotifier2D.

Partial code:

var active = false

func _process(delta):
    if active:
        play_animation()
        move()

func _on_VisibilityNotifier2D_screen_entered():
    active = true

func _on_VisibilityNotifier2D_screen_exited():
    active = false

Comments

comments powered by Disqus