getting_started/first_3d_game/05.spawning_mobs

[giscus[bot]]

getting_started/first_3d_game/05.spawning_mobs

In this part, we're going to spawn monsters along a path randomly. By the end, you will have monsters roaming the game board. image0 Double-click on main.tscn in the FileSystem dock to open the Mai...

https://docs.godotengine.org/en/stable/getting_started/first_3d_game/05.spawning_mobs.html

[Catley94]

Also worth mentioning that as per the 2D Tutorial, you can grab references to child nodes using $ also.
So this:
get_node("SpawnPath/SpawnLocation")
can also be referenced like this:
$SpawnPath/SpawnLocation

I like how both tutorials show to do this two different ways (though using get_node is mentioned in a note in the 2D tutorial).

[v-kydela]

In addition to being shorter, I would say your way offers better functionality because then the variable has the right type

[miguelcondesantos]

If the mob is not spawning you'll probably have to get the Timer Node on the Main Script

public override void _Ready(){
		var mobTimer = GetNode<Timer>("MobTimer");
		mobTimer.Timeout += OnMobTimerTimeout;
}

[IrisRealtime]

Thank you for this correction. This missing code seems to fixed the warning about connected method being missing.
However, I believe I also need to write such code for Mob.cs (im using C#) file as well, but I can't quite figure out what to write or what did I wrote wrong.
Could you perhaps comment on the previous page what to write in that part of code, specifically about connecting OnVisibilityNotifierScreenExited?
Thank you

[Reinky]

You don't need to write additional code for that.
Tldr: If you're using C# you have to first create method in your C# Script and then connect it to signal after rebuilding project, as it doesn't happen automatically, like when using GD Script.

Instruction for connecting to signals using C#:

1. write method that you want to connect to singnal (in your case OnVisibilityNotifierScreenExited() that was provided in this tutorial).
2. Rebuild your project,
3. Go to signal you want to connect to written method(in your case it will be screen_exited() signal in VisibilityNotifier3D).
4. Press Connect in context menu of the signal
5. Press "Pick" button in "Receiver Method" part of the menu.
6. Select your method(OnVisibilityNotifierScreenExited()) in the opened method list.

[miguelcondesantos]

it didn't work I still had to get the node

[msyverw]

For some reason, my mobs are sometimes spawning with an X rotation, making their tails clip into the ground. It seems to happen during the LookAtFromPosition(startPosition, playerPosition, Vector3.Up); function. Any ideas on what could be causing this?

[VinceCefalu]

I got the same thing. Turns out that if the player has jumped when a mob is spawning, the mob will angle itself to point upward at the player. I fixed this by setting playerPosition.y = start_position.y before the line you mentioned. You could also set it to 0 but I think I raised the model a bit on mine so just to be safe I didn't hard code it.

[LilLucas47huntingdaleroad]

Come to my house

[RensTillmann]

I believe you can just set player_position.y = 0 right before calling look_at_from_position() in that case.

[M1ck3y07]

hello, I keep getting the red text saying "Cannot call method 'instantiate' on a null value" whenever I press F6, it directed me to line 7 of the code but im not sure what is wrong with it, I even copy pasted the exact code from the tutorial but i'm still getting the same issue.

There is a yellow line pointing towards line 7 where I've put:

var mob = mob_scene.instantiate()

Is there supposed to be something else in this line?

The code I used:

extends Node

@export var mob_scene: PackedScene 

func _on_mob_timer_timeout():
# Create a new instance of the Mob scene.
	var mob = mob_scene.instantiate()

# Choose a random location on the SpawnPath.
# We store the reference to the SpawnLocation node.
	var mob_spawn_location = get_node("SpawnPath/SpawnLocation")
# And give it a random offset.
	mob_spawn_location.progress_ratio = randf()

	var player_position = $Player.position
	mob.initialize(mob_spawn_location.position, player_position)

#Spawn the mob by adding it to the main scene.
	add_child(mob)

Thanks

[VinceCefalu]

Have you checked if you assigned the mob.tscn file to the mob_scene var in the inspector (right side panel)? If nothing is assigned there, it will always be null since nothing is assigned to that var in the code.

[M1ck3y07]

It's working now, thanks everyone :)

[Berniesaxers]

Could you detail what the problem/solution was? I'm having the same issue and struggling to find the problem.

extends Node

#Brings the mob scene to the main scene
@export var mob_scene: PackedScene



func _on_mob_timer_timeout():
	#Create a new instance of the Mob scene.
	var mob = mob_scene.instantiate()
	
	#Choose a random location on the SpawnPath, store it in the SpawnLocation node
	var mob_spawn_location=$SpawnPath/SpawnLocation
	#And give it a randon offset
	mob_spawn_location.progress_ratio=randf()
	
	var player_position=$Player.position
	mob.initialize(mob_spawn_location.position, player_position)
	
	#Spawn the mob by adding it to the Main scene
	add_child(mob)

[Berniesaxers]

Nevermind, I found/fixed the problem. I had yet to assign the mob.tcsn file to the main scene's var, but i still had an error code reading "Invalid call. Nonexistent function 'instantiate' in base 'GDScript' " so i started troubleshooting the mob.gd file until i realized that i may not have attached it as a script to the Mob node... and that was the problem.

[chihwahli]

there is way to write it in code instead of using the UI to add a scene. It has it's benefits:
@onready var mob_scene : PackedScene = preload("res://scenes/mob.tscn")
In some cases you loose all UI settings , and you have to add the scenes again 1 by 1. with code, no problem!

[shoul]

I fixed the error by declaring the variables with type. It is also good style to do this. The framework tells you when you are overriding an existing variable or function. My function looks like this:

	func _on_mob_timer_timeout() -> void:
		# Create the variables
		var mob: CharacterBody3D
		var mob_spawn_location: PathFollow3D
		var player_position: Vector3
		
		# Create a new instance of the Mob scene.
		mob = mob_scene.instantiate()

		# Choose a random location on the SpawnPath.
		# We store the reference to the SpawnLocation node.
		mob_spawn_location = $SpawnPath/Spawnlocation
		# And give it a random offset.
		mob_spawn_location.progress_ratio = randf()

		player_position = $Player.position
		mob.initialize(mob_spawn_location.position, player_position)

		# Spawn the mob by adding it to the Main scene.
		add_child(mob)

Maybe this is interesting for someone.

[shoul]

Well, I'm not sure if I have fixed the error like that. I have changed it back and can no longer trigger the error. Maybe there was another error in the cash or so??? But the error is no longer occurring and I would like to know what caused it, especially since others with the same code had the same error.

[MattiArtin]

Just wanted to mention I had an error where the mobs were spawning and travelling, but seemed to all be travelling on the Vector3.UP, despite the correct code happening.
Not entirely sure which one fixed it either, but declaring the Variable type for everything did manage to fix the problem.
Even tried your approach and changed everything back after it was fixed, and everything was still working fine as if the var types were still defined.

Wouldn't have thought of this myself, so wanted to say thank you for the idea!

My only theory is that changing from dynamic variables to static variables for player_position gently nudged GDScript into identifying the correct variable type. But since that was the only plausible option for that variable it resulted in understanding what to look for and it somehow cached that since it was the only logical choice?

Tis a mystery to me ~

[MattiArtin]

Woops, I meant to say the mobs were travelling Vector3.FORWARD, not Vector3.UP.

[vmorris]

It should be a MeshInstance3D instead of MeshInstance.

[vmorris]

Maybe I'm doing something wrong..

In the Inspector, expand the Material section and assign a StandardMaterial3D to slot 0.

For the MeshInstance3D nodes, the inspector field is called "Surface Material Override".

[Calinou]

MeshInstance is the Godot 3.x name for MeshInstance3D. All 3D nodes have a 3D suffix in Godot 4.x, while only some of them had it in Godot 3.x.

For the MeshInstance3D nodes, the inspector field is called "Surface Material Override".

This is not the same property as the Material property on a Mesh resource. Surface Material Override overrides existing surface materials that meshes may have assigned, so it serves different use cases.

Surface Material Override is best used when you want a single instance to use a different material from all other instances in a scene.

[Bacteriofak]

Hi everyone!!!
In my case there was this error:
E 0:00:00:01:0424 main.gd:11 @ _on_mob_timer_timeout(): Node not found: ‘SpawnPath/SpawnLocation’ (relative to ‘/root/Main’).
<C++ Error> Method/function failed. Returning: nullptr
<C++ Source> scene/main/node.cpp:1792 @ get_node()
main.gd:11 @ _on_mob_timer_timeout()

I fixed it this way:
The tutorial says this:
var mob_spawn_location = get_node(‘SpawnPath/SpawnLocation’)

I corrected it to:
var mob_spawn_location = get_node(‘SpawnLocation/SpawnPath’)

Strange, according to the tutorial the hierarchy is specified as SpawnLocation child node SpawnPath, why is it the other way round in the code?

[PlagueKina]

Why does when i press F6 my game starts but there is always a mob model that does not move under the player model?

[JosePadinha]

Most likely you have a mob node in the Main scene so it doesn't spawn using the initialize script that gives it position and velocity

[Boddikan]

I had a similar issue.

Make sure to check your mob.gd script Vector3 inputs are correct. My look_at_from_position function input was set to Vector3.ZERO instead of Vector3.UP:

look_at_from_position(start_position, player_position, Vector3.UP)

[SummationX]

I have a problem on the part where you place the cylinders, my view of the camera can see the edge of the floor, so if I fill the floor and place the cylinders, the cylinders are so far apart compare to the image above

[Curistofa]

Godot 4 doesn't seem to have the option to toggle the visibility of a regular Node (unless im doing something wrong)

I can see the eye icon next to all four MeshInstance3Ds, but not next to the Cyclinders node itself

[Calinou]

Indeed, you have to toggle visbibility on the child nodes individually. Node has no concept of visibility, since it also has no concept of a transform (position/rotation/scale) or any kind of visual representation.

[fromAnightmare]

The Cylinders node is supposed to be Node3D (it's beautifully colour coded Red), not just Node(white). They are different. and I do have the option to toggle visibility of it node. Unless that is a change that has been introduced for Godot 4.4.

[Fhenomenal]

I've ran into a snag, My mobs aren't moving around. they're spawning but static, they also seem to be facing towards the same location on spawn. I've switched the code i writ with the provided code. i assumed it was something to do with creating the SpawnPath and SpawnLocation but have recreacted to no avail.

if more information is required i will provide. Thanks for reading :)

[fromAnightmare]

I just did too. You probably figured it out for yourself, but for everyone else:

Check your mob.cs or mob.gd (the previous page) check the last 2 lines of code in the Initialize method.

I didn't write in vector3 but velocity, I'm guessing autocomplete on VSCode. They were spawning but not moving, as they had no forward momentum.

Hope this helps someone

[freakyfrogboy24531]

The mobs aren't spawning for me

[freakyfrogboy24531]

I fixed the problem
turns out they were all below the floor
I just had to move everything closer to the grid

[Menekrr]

The mobs and the player in the screenshots in this tutorial has a glazed, shiny look. But when I run the program, the mobs and the player have this matted / satin spray-painted look. XD

[Calinou]

This is likely because you have the preview environment and light enabled, but you didn't add them to the scene. You can do so by clicking the 3 vertical dots at the top of the 3D editor viewport, then choosing Add Sun to Scene and Add Environment to Scene. See Environment and post-processing for details.

[Menekrr]

Hi Calinou, thanks for the message!

I added the Sun and Environment to the Main, Mob, and Player scenes, and, when I ran the game, everything looked so brightly lit that everything was white-washed, and flickered a bit as if clouds were flitting by at surreal speeds. Player and Mob movement was also very low-performance and laggy. And after about 3 seconds or so, the game crashed with no error messages.

I then deleted the WorldEnvironment and DirectionalLight3D from both the Player and Mob scenes, keeping the WorldEnvironment in the Main scene, and the flickering, white-washing, crashing, and low-performance all went away. But my characters still looked like they have a satin spray-painted look, not the glazed look in the tutorial screenshots.

So I guess that adding the sun to all 3 scenes was the cause of the white-washing, hahaha!

Do you think that the tutorial screenshots were from a previous version of Godot and hence the differences in appearance, and I might have to change the materials in the 3D models to affect the way they appear?

I'm using a MacBook Pro Retina, Mid-2014:
Godot 4.3 stable
macOS Catalina 10.15.7
CPU: 2.5 GHz Quad-Core Intel Core i7
Memory: 16 GB 1600 MHz DDR3
GPU: NVIDIA GeForce GT 750M 2 GB; Intel Iris Pro 1536 MB

[Calinou]

Do you think that the tutorial screenshots were from a previous version of Godot and hence the differences in appearance, and I might have to change the materials in the 3D models to affect the way they appear?

Yes, the screenshots were made with Godot 3.x. Godot 4.x renders lights a bit differently for a few reasons (different scene shader, different light attenuation model, sRGB blending for lights with shadows enabled in Compatibility).

[Menekrr]

Thank you for the clarification!

[navisud]

Hello everyone, my mobs are spawning above the player. I don't have any idea why this is happening. How can i fix it?

[Axelmdez]

If you're adding something to the scene, by default it'll appear at (0,0,0). That's probably where you still have your player. If you keep spawning things at the same coordinates they will stack on top of each other.

Make sure you are setting a position for the mob before adding it to the scene. This should be where to look first

var player_position = $Player.position
mob.initialize(mob_spawn_location.position, player_position)

[resnickmicah]

I had this problem because the points along the SpawnPath's Curve3D had really high Y offsets. I edited the points in the inspector to have Y = 1 and that fixed it.

[AndrewMacchioccini]

Hello, i'm getting this error and i have no idea what's wrong:

Invalid type in function 'look_at_from_position' in base 'CharacterBody3D (mob.gd)'. Cannot convert argument 1 from Object to Vector3.

[AndrewMacchioccini]

Solved, i just forgot to write .position

[Biohazard980]

Same issue I was having,
To elaborate on what he means by .position
it is in main.gd, second to last line

mob.initialize(mob_spawn_location.position, player_position)
                                  ^^^^^^^^

Hope this helps anyone else that couldn't find it. Took me a while myself haha

[JalBrew]

Oh goodness thank you so much, I was stuck in this for around 4 hours trying to figure out what went wrong.

[Tridacnid]

I noticed that placing the points to create SpawnPath in the editor is difficult and any variance in y axis for the points will cause the Mobs to sometimes generate with a y "tilt" pointing either slightly up or slightly down as they target the player. This is exacerbated when the player jumps and, while in the air, a new mob spawns. I ended up "normalizing" the y plane to 0.5 for both spawn location as well as the player's location when sampled for spawning a mob to keep them firmly on the xz plane, but a more elegant/robust solution in the instructions would be appreciated.

[Jacinto73]

Am I supposed to move the mesh instance or the cylinder node containing it while scoping out the path? I find it more productive to ask than waste a lot of time. I'm old for this. I played Pong when it was breathtakingly cutting edge.

[Jacinto73]

N/m figured it out.

[azure-argen]

i need some help its giving me error in the player position line saying there is no player the tutorial does say something about player in the main scene but idk how to fix this can anyone help me out on this?

[SnuSnuWarrior]

Hey team,

Im a noob and still trying to navagate through this. Im stuck due to this error message "script inherits from native type characterbody3d so it cant be assigned to an object type: Node 3d" Dose anyone have a solution for this?

Thank you

[SnuSnuWarrior]

All good im a idiot, My Mob node was a node 3d not a Character3d

[DeclanKehoe]

Is there a way of having the editor show a hint for the custom functions we add in the scripts attached to our nodes (sorry if I mess up terminology, I'm still very new to Godot)?

For example, we give the Mob node in mob.tcsn an initialize function within its attached mob.gd script (I spelled it initialise btw, which is what made me think to see if autocomplete worked). When I instantiate a new Mob scene and assign it to the variable mob in main.gd, the custom initialise function doesn't show up in autocomplete when I start typing mob.in...

I thought providing a type when declaring the variable might help, but var mob : CharacterBody3D = mob_scene.instantiate() made no difference. It also might just be the incorrect type. So, is there something I need to do to make the function 'hintable' in mob.gd, or am I missing something obvious?

[Anonyme]

Hello,

I followed this section of this tutorial but when I try to test I'm facing the following error:

E 0:00:01:758   PackedSceneExtensions.cs:20 @ T Godot.PackedScene.Instantiate<T>(Godot.PackedScene+GenEditState): System.InvalidCastException: Unable to cast object of type 'Godot.Node3D' to type 'Mob'.
  <Erreur C#>   System.InvalidCastException
  <Source C#>   /root/godot/modules/mono/glue/GodotSharp/GodotSharp/Core/Extensions/PackedSceneExtensions.cs:20 @ T Godot.PackedScene.Instantiate<T>(Godot.PackedScene+GenEditState)
  <Pile des appels>PackedSceneExtensions.cs:20 @ T Godot.PackedScene.Instantiate<T>(Godot.PackedScene+GenEditState)
                Main.cs:12 @ void Main.OnMobTimerTimeout()
                Main_ScriptMethods.generated.cs:34 @ bool Main.InvokeGodotClassMethod(Godot.NativeInterop.godot_string_name&, Godot.NativeInterop.NativeVariantPtrArgs, Godot.NativeInterop.godot_variant&)
                CSharpInstanceBridge.cs:24 @ Godot.NativeInterop.godot_bool Godot.Bridge.CSharpInstanceBridge.Call(nint, Godot.NativeInterop.godot_string_name*, Godot.NativeInterop.godot_variant**, int, Godot.NativeInterop.godot_variant_call_error*, Godot.NativeInterop.godot_variant*)

Any ideas of what can cause this error ?

Thanks

[chihwahli]

Without your code it is not easy to guess.

[playhorsejr]

What do i do if i dont have the mob.tscn in the files section

[chihwahli]

it is created by you, slowly look through the tutorial where that is.

[playhorsejr]

ok, i think i got it, thanks

[treyhakanson]

In GDScript, is it possible to type the mob var instantiated from the mob_scene as the class defined in the mob script? It'd be nice to get warnings/autocomplete on methods like initialize

[knightmb]

On the step "Rename the two nodes to SpawnLocation and SpawnPath, respectively. It's more descriptive of what we'll use them for.", the instructions are correct, but the picture is wrong. If you try to correct your node setup to the picture, it will cause the F6 test scene to fail with a path error. I didn't see any mention of it in the comments here, so I think most have figure out it from the error output, but just in case it stumps someone in the future. 👍

[feelikeanimal-wq]

Getting such error when clicking F6, scene loads but freezes instantly:

 <C++ Error>   Method/function failed. Returning: nullptr
 <C++ Source>  scene/main/node.cpp:1877 @ get_node()
 <Stack Trace> main.gd:12 @ _on_mob_timer_timeout()```

Seems like I did everything according to the guide, any help appreciated. 

[benbgodot]

HI. First time writing code again since BASIC in the early 90s. Following along the guide. I'm on 4.4.1, MacBook Pro 2020 if that helps. Mines not working as expected. I have spent probably 6-8 hours now going through all of the code, the manual, trying little fixes etc. Not working. I even just hit "copy/paste" on your code summaries at the end onto my screen figuring I would take it from the horses mouth so to speak. not working. 2 Problems:

1. Mobs are spawning in one place - either once or infinitely on top of each other. No way to tell.

2. Player can move around the map for about 10 seconds before the game stops moving him to new coordinates. But its not frozen - i can change the direction it is facing. It just stops moving to new coordinates.

I considered just accepting as is for now and continuing the lesson - but it would seem these two issues are important to resolve for the game to function properly.

Thank you!! Benbgodot

[benbgodot]

worth maybe mentioning - I get added functions/scripts on my coding by adding in the added node sensors. I have left them in at the bottom. have greyed them out using a #. none of it makes any tangible changes. Should I copy paste my codes from all 3 for easier audit? main.gd; mob.gd; player.gd
thanks

[v-kydela]

The mobs spawning in one place sounds like you didn't get the Path3D set up correctly. But the player getting stuck sounds like maybe the mobs are getting their collision shapes separated from their graphics. What happens for me at this point is the screen gets filled with a cluster of mobs that have all crashed into each other and stopped moving, so they could potentially box the player in. If fixing your Path3D doesn't work, I recommend just starting the tutorial over from the beginning since it's hard to say what you might've missed

[jcutts]

Hello, one issue I had with the mobs not showing was that my floor was up to high. Lowering the floor solved my problem.

[Roleander]

Hi folks!
Why do I get this error when pressing F6 in this chapter of the game?
Thanks!

[Roleander]

This is the error I get:
Invalid assignment of property or key 'progress_ratio' with value of type 'float' on a base object of type 'null instance'.

[v-kydela]

Your mob_spawn_location must be null. Is the main.gd script attached to the main node, and does it have a child node named SpawnPath with a child node named SpawnLocation?

[Roleander]

Yeah, I currently have this on my main.gd =

"var mob_spawn_location = get_node("SpawnPath/SpawnLocation")
mob_spawn_location.progress_ratio = randf()"

Should I change this to 0 or null instead?
I also have a Path3D with SpawnLocation and SpawnPath attached to the main node as this guide says.

[v-kydela]

If it's null then get_node must be failing. The most likely explanations are that you haven't set up the hierarchy correctly or the script is attached to the wrong node

[and22122]

I'm running into an issue where all of my characters (including both the mobs and the player character) are moving about in a seemingly random way. Instead of moving in straight lines they move in sort of a random walk, with the player character moving even without input. Has anyone run into this kind of issue? Does anyone have suggestions for me?

[Calinou]

Check your collision shapes' sizes using the Debug > Visible Collision Shapes option at the top of the editor (then re-run the project). Maybe you set the collision shapes too large, which causes mobs and the player to constantly collide with each other. This will make them shake around constantly.