Please Help me understand basic signal

Gowydot

Why is this not working? Area and Cars are instances , Expect result: cars cars Thank You

Tree: Spatial -Area -Car -Car2

Area:

extends Area

signal say

func _ready():
		emit_signal("say")

Cars:

extends KinematicBody


func _ready():
	connect("say", self, "_say_cars")

func _say_cars():
	print("cars")

xyz

connect() should be called as a method of an object that is the source of a signal. So at line 5 in car script connect() needs to be called on Area object: $"../Area".connect("say", self, "_say_cars")

Also your signal may fire too early, as emit_signal() probably executes before connect() in this scene setup

cybereality

The signal needs to be defined in any script where the signal is used. So:

signal say

Needs to be at the top of both scripts. Also, you need to connect with the object that is emitting the signal. In your code the connect function is running on that script, meaning it will only see emits from that script, not others. As @xyz says, having both calls in ready may not work because it would depend on how the tree is processed (the ready calls get called in a specific order based on the hierarchy). It would be better for testing to add an input and press a key to emit the signal so you can test it works.

Gowydot

I see. So it is not like Area is emitting a "say" but more like emitting that it has a "say" in its code and if anyone want come in and get it. And in my case Car needs to go up the tree first to connect with its Area sibling. (*I moved Area to the bottom of the tree for this test to work)

fire7side

Connecting with the node tab in the editor is a sure fire way of knowing you have a connection, also. Once you define it in your script, it will show up in the connection options and write a function for you in the receiving script.

xyz

@Gowydot said: I see. So it is not like Area is emitting a "say" but more like emitting that it has a "say" in its code and if anyone want come in and get it. Almost like that. When you declare signal say, Area announces to everyone who is interested that it may emit say now and then. So everyone who is interested in knowing when say happens can establish a connection with Area (either via gui or connect function) and supply a callback function that Area will call whenever say happens. Calling Area.connect("say"...) is like saying: "Hey Area, whenever say happens, call me immediately at this number"

Gowydot

@fire7side said: Connecting with the node tab in the editor is a sure fire way of knowing you have a connection, also. Once you define it in your script, it will show up in the connection options and write a function for you in the receiving script.

My problem right now is that I'd have to manually connect (via node tab) Area signal to 10-20 Car instances (From my pathfollow thread)

Can anyone show me ways to make Area to signal to all Car instances for this simple setup? I'd like to understand it first, Thanks

cybereality

Honestly, I find connecting via code to be easier. The editor connection is okay for simple stuff, but it's more flexible to do it with code (like you say, if you have 20 objects). Also if you need to edit the function names or whatever, it's much simpler to edit a script.

cybereality

If you want to find all instances of Car, you can add the Cars to a group and then call this:

var cars = get_tree().get_nodes_in_group("Car")
for car in cars:
   # do something to the car, such as connect

You do have to add the Car to the group "Car" first for this to work.

Gowydot

Hi, I could connect to all car instances but still unable to make them react "individually" (each car should stop only when hit Area)

Tree: World -Car -Car2 -Area

Area:

extends Area

signal hit

func _on_Area_body_entered(body):
	emit_signal("hit")

Car:

extends KinematicBody

var speed = 10

func _ready():
	add_to_group("Car")
	var cars = get_tree().get_nodes_in_group("Car")
	for Car in cars:
		$"../Area".connect("hit", self, "_stop")
 
func _process(delta):
	var velocity = Vector3.ZERO
	velocity.z -= speed * delta
	move_and_collide(velocity)
	
func _stop():
	if self.is_in_group("Car"):
		print("stop")
		speed = 0
	else:
		print("fail")

fire7side

That's probably not a good place for a signal. You would probably want to get overlapping bodies in the body entered function, check if it's a car, and then call the stop function. They all hear the signal and stop.

Gowydot

Hi, I found this city project and from your advice I finally figured out how it works and applied to my little setup. (Using editor signal though but learning to do via code is cool too) so Thanks all

Main Tree: World -Area -Car -Car2

Car Tree: KinematicBody -MeshInstance -CarArea --CollisionShape

Area:

extends Area

func _on_Area_area_entered(area):
	if (area.name == "CarArea"):
		print("hit")
		area.get_parent().speed = 0

Car:

extends KinematicBody

var speed = 10

func _process(delta):

	var velocity = Vector3.ZERO
	velocity.z -= speed * delta
	move_and_collide(velocity)

fire7side

That looks like a cute project. I'm downloading it. Glad you got it working.