Bring Curve2D editing plugin to exported variables in any custom nodes

[Exerionius]

Hello everyone.

There is a great built-in addon for editing Curve2D (think of bezier curves) in the editor: https://github.com/godotengine/godot/blob/master/editor/plugins/path_2d_editor_plugin.cpp

But this plugin works only on the Path2D node. If the user exports a Curve2D variable in their custom node, the editing functionality is not there:

tool
class_name TestNode
extends Node2D

export (Curve2D) var curve

If the plugin is already there, why not to enable it for any Curve2D exported variable?

Currently I have to create a temporal Path2D node just for editing a curve, saving it into a file resource and loading back into my node, because it's impossible to edit it on the node itself.

Imagine if you have something like this:

export (int) ammo

And you need to create a separate special node just to edit this value before loading it back into your exported variable every time you need to adjust it in the editor.

[Xrayez]

I'd say this is a major limitation with editor plugins in general. Or rather, those plugins that require Godot's canvas item editor.

The same issue is present with NavigationPolygon, OccluderPolygon2D, Shape[2D], and likely others.

For example, a VisualShape2D that you can find in Goost cannot edit the Shape2D resource directly, unfortunately. Reusing the same editor plugin for custom nodes is currently impossible, and reimplementing those plugins is frankly impractical. See also #1126, #1157.

[Exerionius]

The question is - how difficult it is to reuse it, considering that the functionality is already there.
I'm not familiar with Godot sources and my C++ is rather rusty, so I can't really tell myself.

[Xrayez]

First, the plugin has to be exposed to scripting. You can verify this is not the case currently. The only specific plugin I see there exposed is AnimationTrackEditPlugin, and probably a few others.

Second, the source code directly relies on whether a node is selected. For this to work directly on a resource, it has to handles() the resource directly (Curve2D). So this requires C++ core modifications in either case. The rest of functionality probably doesn't need to be modified as much. Perhaps there will need to be created a new plugin that would extend the base, so that the plugin could edit both the node containing the resource, and the resource itself.

[mutualtape]

Had the same need and came up with this workaround in my custom node plugin that works well enough for a smooth workflow. It creates a Path2D on the fly (I use the method to add other nodes like collision etc. too) and adds a listener on changes to the curve.

@tool
@onready var curve_node: Path2D = lazy_add_to_scene("Curve", Path2D)
	
func lazy_add_to_scene(name, clazz: Variant):
	var node
	if(has_node(name)): node = get_node(name)
	else:
		node = clazz.new()
		node.name = name
		if("curve" in node): node.curve = Curve2D.new()
		add_child(node)
		node.owner = get_tree().edited_scene_root
	return node	
	
func _ready():
	if(Engine.is_editor_hint()):
		curve_node.curve.changed.connect(func(): 
			# copy curve to other persistent nodes:
			a_collision_node.polygon = curve_node.curve.get_baked_points()
		)