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Custom resource not showing as default in export variable?

I've made a custom resource and I want to load it as a default in an export variable so I've tried this:

extends Node2D

export(Resource) var custom_res=CUSTOM_RESOURCE.new()

and my custom resource script as such:

extends Resource
class_name CUSTOM_RESOURCE

export var data=10

but for some reason it doesn't seem to show up within the editor:

enter image description here

am I doing something wrong?
shouldn't the editor display the custom resource as default whenever the scene is instanced like this?:

enter image description here

Solution

  • Running the initialization in the editor

    That initialization is not running in the editor, only when the game starts.

    You know the solution is tool:

    tool
extends Node2D

export(Resource) var custom_res=CUSTOM_RESOURCE.new()

    And all that comes with it. For people finding this form search, be aware of Engine.editor_hint.

    Setting the default value

    Turns out the reason we need the initializer to run is because what we are setting (CUSTOM_RESOURCE.new()) is not constant.

    We can confirm that with a simple constant, for example:

    export var x := 5

    In that case the initializer didn't run in the editor per-se. Instead Godot set the constant was set as the default value when it parsed the script. And that is what we see in the Inspector.

    So we want a constant value of our custom resource. Well, preload is a constant expression (preload is a keyword not a method). And yes, it is resolved while parsing. And yes, Godot will set it as default value, despite it not being a primitive type. Thus we can preload a resource file and use that, for example:

    export var custom_res:Resource = preload("res://new_resource.tres")

    Which, of course, requires that we have resource file to preload. We can create it from the context menu on the FileSystem by selecting "New Resource…", then picking our custom resource class, and a file name to save it.

    Notice this differs from running the initializer in the editor in that:

    1. It does not require tool and all that comes with that.
    2. With tool, the default value remains (null). So you will see the arrow to reset the value in the editor, and clicking it erases the value of the property.
    3. Your custom resource object will be the default value. So you won't see the arrow to reset the value right away. And if you modify it, resetting it the value gives you your resource object back.

    Gotcha: Everywhere you preload the same resource file, you get the same resource object. Modifying it will modify it everywhere. Even across different scenes.