Discuss a way to allow adding behaviour and attributes to a scene via node composition

[azagaya]

I was wondering if there could be a way to improve the scene composition to be able to make scenes have extra behaviors and/or attributes by just dropping nodes on the scene.

For example, lets say we have many scenes that need to have a health attribute and a take_damage method. And i dont want to repeat the same code everywhere when i need that.

So, what i tried so far?

Adding a node to the scene with those things

So lets say i add a Health node that has the health attribute and the take_damage method. This works, but makes me do something like:

var health_node = enemy.get_node_or_null("Health"):
if health_node != null:
  health_node.take_damage(damage)

While with having the attributes in the script itself was only:

if enemy.has_method(take_damage):
  enemy.take_damage(damage)

Ok, is just a line, but if you have to do this in a lot of places, it kind of annoys you. Moreover, if i instance this scene in another scene and want to change the health, i have to make children editable, which has other downsides.
Another problem is that you must force nobody in the team use Health as a node name for other thing.

Inheriting from a base class that has those things

This works and ive used it a lot. But if you need an Area to have this, then a StaticBody, then a KinematicBody, and so on, you will end up repeating code, as extending a node that is inherited by all of this is not advisable.

Node + Autoload

What ive also done is to have a scene Health and an autoload HealthSystem. So when i need to do damage i do:

HealthSystem.make_damage(reciever, dealer, damage)

And the HealthSystem is in charge of doing the checks. I still cannot customize the health from the scene tree when i instance a scene.

Resources

I can export a var to hold a resource for this, and mark it as local to scene. However i need that export in every script that needs it, and mark them as local for everything too.

Do Traits solve this?

This will be greatly aliviated when gdscript includes traits, as i could simply do use HealthTrait in the script. However this will only be for compile time (like 90% of my uses cases anyways).

What i would like

I would like to be able to throw a node into a scene, and its methods and attributes be exposed directly in the Owner of the scene. For example Qt Quick works with a similar tree based approach, and has a button that expose certain things as aliases in the root node. However Qt Quick does it by modifying the script and this is not advisable imho for godot.

But it would be nice if, similar to the unique name feature, i could "Mark this node as attribute", and the exported attributes of that node get exposed as if they belong to the owner of the scene. Moreover, i would like that if i select an instanced scene that has this kind of "attribute nodes", i could see the attributes in the inspector. Like a subresource. Something similar with methods.

Or perhaps a keyword as we have for @tool, for example, if you use @attribute in a script the exported variables, and the methods get exposed in the owner of the scene where a node with this script is.

This way i could just drop a node to add functionality in a seamless and trasnparent way. Just throwing nodes to the tree, as we always do in godot. No need to modify scripts or whatsoever.

I didnt make this a proposal because im not sure if this makes sense for how is godot built now, but i believe the workflow would be more "godot" than the other approaches i used

[vnen]

I believe you want something similar to what #361 proposes.

[azagaya]

I believe you want something similar to what #361 proposes.

Is very similar, and is a great proposal imho yeah.
But is not quite the same. In my opinion, it would be better if you dont even have to add that export to the script. Because that way you can increase the code reuse. I usually have kinematics that move exactly like enemies, but are not enemies and thus they cannot recieve damage. If i could just drop a Health node to the enemy scene and make it automatically expose it properties would be even better. If not, im forced to have different classes that are almost identical except for the health part (because one of them need to give a reference to the health node and the other no). One may say "Then make the movement reusable", but if my root nodes are kinematics, the movement needs to be there, in the root of the scene. Having the movement in a sepparate node is not convenient.

So, that proposal is great and would make my life easier in a lot of cases, but i really would like a codeless node composition. Just drop a node in the scene and the scene now have this characteristics.

[azagaya]

Btw, thats why I added this in editor category. If its possible i would like a solution in the editor. Something like the "make this node unique" but "make this node exposed" or "make this node public". And another difference, i dont want to expose a reference to the node, i want to expose the exported variables and the methods of the script of that node, as if they belonged to the owner of the scene.