understanding call_group

jonobugs

Hi, I'm new to Godot and I'm trying to figure out get_tree().call_group

It seems to work just fine in some of my scripts where the player gets hurt or collects coins but in another script I try to call it and I get nothing. I don't think it's calling the functions at all but I really can't figure out why.

from my player.gd (works):

get_tree().call_group("Gamestate", "end_game")

from hazards.gd (works):

get_tree().call_group("Gamestate", "hurt")

from coin.gd (works):

get_tree().call_group("Gamestate", "collect_coins")

from GameOver.gd (does not work):

get_tree().call_group("Gamestate", "get_level")

I double, triple checked the spelling of the function. I don't think it's getting to the function because nothing happens, not even an error. I wrote a simple print statement just to see if it got there but nothing was printed. I'm positive that the games gets to the call_group command though.

I'm wondering if there is a situation where the call_group will not work.

Thanks for any help!

TwistedTwigleg

Welcome to the forums @jonobugs!

Does get_level return a value or have additional arguments? It could be that, if it has additional arguments especially, it is looking for the function with no arguments and because it cannot find any it simply skips.

jonobugs

Does get_level return a value or have additional arguments? It could be that, if it has additional arguments especially, it is looking for the function with no arguments and because it cannot find any it simply skips.

    func get_level():
    	get_tree().change_scene("res://Scenes/Levels/Level%s.tscn" % level)

No, I'm trying to change the scene.

However, I think I may have figured out the problem. (not the solution though). I'm calling that code AFTER I change to a "try again" scene. I use:

get_tree().change_scene("res://Scenes/Levels/GameOver.tscn")

I think that when you change scenes the data gets wiped, so I guess Godot doesn't know that Gamestate is a group anymore since it's called in the script.

I don't want to use Autoload (singleton) because it tends to mess up the rest of my code.

I've been trying to figure out a good solution to carrying data across scenes. I'd rather not use save data because I kind of want the game to start at level one each time it's played, which is why I tried using groups. I thought that would work, but it doesn't seem to because it resets. I read that you can use static classes in Unity, but I have no idea how to do that with Godot or if it would even work.

Thanks for checking my question and welcoming to Godot! I love this program but I'm so new!!

TwistedTwigleg

Unfortunately, Autoload (singletons) are the only way I know right off to have data persist across different loaded scenes. You could try saving the data to a file or something, but I’m not sure how well that would work.

I do think you are probably right that the issue is trying to call the code after changing a scene, as likely what is happening is that the scene changes but the nodes haven’t had a chance to register themselves to the group yet, leading to none being found and the code not doing anything. One thing you could try that might help is adding something like yield(get_tree(), “idle_frame”) right after changing the scene but before calling call_group, so there is a single frame of wait time which should be enough to let the scene register all the groups. I’m not sure if it will work though.

jonobugs

@TwistedTwigleg said: Unfortunately, Autoload (singletons) are the only way I know right off to have data persist across different loaded scenes. You could try saving the data to a file or something, but I’m not sure how well that would work.

I do think you are probably right that the issue is trying to call the code after changing a scene, as likely what is happening is that the scene changes but the nodes haven’t had a chance to register themselves to the group yet, leading to none being found and the code not doing anything. One thing you could try that might help is adding something like yield(get_tree(), “idle_frame”) right after changing the scene but before calling call_group, so there is a single frame of wait time which should be enough to let the scene register all the groups. I’m not sure if it will work though.

Thank you so much for your time. I'll see if I can do that, but I'm also trying another way right now.

I figured out how to grab the filename of the scene that is being played by using:

var current_scene = get_tree().get_current_scene()
print(current_scene.filename)

Since all my levels are in the same place and I will be naming them level1, level2, etc. I just need to figure out how to extract the scene that's being played, strip the last part and figure out what number the scene is, add one and that will be the next level to be played. I'll see if I can get that to work.

jonobugs

I got it!

So, I took the filename and used trim_suffix and trim_prefix to leave only the level, changed that to an int and got the next level.

Thanks for all your input! I guess I'll have to figure out call_group another time.