Git-friendly scene files

[YerkoAndrei]

I think scenes files should only use the GUID for referencing prefabs.

Right now, the scene saves everything of a prefab used on it, but with this format its very hard to work with a lot of people.

Say someone is working on the prefabs and another is on the scene, when the prefab is edited, it also edited any scene that use it, not so team-friendly.

I dont know how hard is to implement this, its just a suggestion. :)

[Doprez]

I would be curious as to what the standard is in other engines?

Is your suggestion to use the prefab as the source of truth or to only use it for instantiation and have the scene handle the values?

I personally like that when I edit a prefab I can expect it to change any of the references that are in a scene but I purely use this as a fun hobby and as a solo dev so Im not sure what other people may expect or want.

[Doprez]

Ah ok, that makes sense. So it would cut down on the amount of merge conflicts created from having all of the unedited data of a prefab being saved?

[YerkoAndrei]

exatly

[Doprez]

I think this makes a lot of sense.

Tagging @manio143 and @IXLLEGACYIXL since they may have some helpful input on this with their serialization knowledge.

[manio143]

I think the reason it's currently implemented as a full object copy into the scene is to save on prefab lookup during asset initialization. The scene asset is independent of the prefab asset, except when your editing the prefab and need to propagate the changes. Otherwise, when compiling a scene you need to make sure you have a reference to the prefab to merge the properties. And with nested prefabs you'd need some kind of caching of the merged layers to make it performant and not do merging all the way down every time.

That is not to say that this is how it should be. I agree that having just changed properties could be easier for source control. The current archetype system has been designed in a specific way across a few different editor/serialization modules and we'd need to understand how it could be modified.

You may want to ping Kryptos for some historical context.

[Kryptos-FR]

I don't think it is feasible to just have the object id. We wouldn't be able to support nested prefabs or the fact that you can override only a part of it, if the whole structure wasn't copied over.

Our prefabs support more use cases than Unity, so comparing with it isn't the whole picture.

I understand the potential issue with team work, but it isn't simple to do it differently. It wasn't done just as a way to make it faster to resolve. And also, as was written it is sharing that mechanism with archetype. It's not trivial to change that.

[IXLLEGACYIXL]

how do you imagine a yaml to look and how it should be resolved , also which values should be serialized, how should default values be evaluated and such

what is the dream case you can imagine it to be

[YerkoAndrei]

I think that only the ID and the changes should be serialized.
I dont know how unity load everything, but when you add a prefab in a scene, it only add the GUID.
I imagine that Unity search for that and it load it after the scene.

I can only tell how i worked with Unity, because that way never gave me a problem, which i know i'll have if i work with Stride with a team.

In this Unity scene, the first GameObjet is a prefab and the second not, and only saves the id of the prefab, it doesnt have changes.

GameObject:
  m_CorrespondingSourceObject: {fileID: 2853423567576865651, guid: b29aac657b977e94aa5d0a01f4b7d7b0, type: 3}
  m_PrefabInstance: {fileID: 1920324864}
  m_PrefabAsset: {fileID: 0}
--- !u!1 &120897676
GameObject:
  m_ObjectHideFlags: 0
  m_CorrespondingSourceObject: {fileID: 0}
  m_PrefabInstance: {fileID: 0}
  m_PrefabAsset: {fileID: 0}
  serializedVersion: 6
  m_Component:
  - component: {fileID: 120897678}
  - component: {fileID: 120897677}
  m_Layer: 0
  m_Name: "SistemaAnimaci\xF3n"
  m_TagString: Untagged
  m_Icon: {fileID: 0}
  m_NavMeshLayer: 0
  m_StaticEditorFlags: 4294967295
  m_IsActive: 1
--- !u!114 &120897677

And in Stride it saves everything, this have a changes (the Deleted ones).

-   Folder: null
            Entity:
                Id: 07607ce9-1595-403c-aeb4-a9249831f41b
                Name: Estatua
                Components:
                    1ff5b84f1e279da93224f2a5edcc3f59: !TransformComponent
                        Id: 9d21e8a8-712c-4ff4-9265-f117b4b6168f
                        Position*: {X: 0.0, Y: 0.0, Z: -5.0}
                        Rotation: {X: 0.0, Y: 0.0, Z: 0.0, W: 1.0}
                        Scale: {X: 1.0, Y: 1.0, Z: 1.0}
                        Children:
                            b9a6de9d3e362d0511a1a20a34248d55: ref!! 93a6666b-a85e-4f79-9908-ae6c6c2d7725
                    65e0ce82b10ff7a08a25a37be73a73db: ~(Deleted)
                    fb06c492109ce5cf0499d7d8846d1f46: ~(Deleted)
                    74bf11dd4dd7e8fa7f6dd5d9df36ec37: ~(Deleted)
            Base:
                BasePartAsset: c957f17f-b857-4560-8c7f-74977bd833cf:Prefabs/Estatua
                BasePartId: 56f5ad60-3d77-4bf7-9c13-cbb046c76088
                InstanceId: 0b77de18-b5b0-46a5-a7ad-e7ec37e4047c

[IXLLEGACYIXL]

the deleted is for asset inheritance , which is hard to implement as you have inherited assets and nested prefabs

if you have a good idea on "how to make asset inheritance" im open for it, as in my yaml serializer i dont know how to implement it
adding a path or something to link to the prefab isnt that "hard" from serialization point of view

thats why i would like to see how you would write a scene or prefab as yaml, how you would see it as an viable option.. mybe pseudo yaml or whatever

its about how to resolve things and how to determine "default" and "equality"

for example you have a list inherited and you delete the third value , in your root prefab you edit the 4th value, through inheritance you gotta change now also the 4th value which is now the third as the other one was deleted.. now what? an example would be good..

[YerkoAndrei]

I dont know how Stride indentifies that an entity is a prefab, but maybe that can be used to deciding to save or not its components and children.

This is how i imagine the file (not knowing much about serialization and how Stride load everything).
(P00003 and n+ are ids in the prefab file)

Entity:
                SceneId: 01
                FileId: 0001
                Name: NotAPrefab
                Prefab: false
                Components: {}
Entity:
                SceneId: 02
                FileId: 0002
                Name: ThisEntityIsAPrefabWithNoChanges
                Prefab: true
                Changes: {}
Entity:
                SceneId: 03
                FileId: 0002
                Name: SamePrefabWithChanges
                Prefab: true
                Changes:
                                P00003 RigidbodyComponent (deleted)
                                P00004 TransformComponent (changed)
                                                Position: {X: 0.0, Y: 0.0, Z: -5.0}
                                                Rotation: {X: 0.0, Y: 0.0, Z: 0.0, W: 1.0}
                                                Scale: {X: 1.0, Y: 1.0, Z: 1.0}
Entity:
                SceneId: 04
                FileId: 0002
                Name: SamePrefabWithListChanges
                Prefab: true
                Changes:
                                P00003 RigidbodyComponent (deleted)
                                P00004 ScriptWithList (changed)
                                                P0004: ref!! 0003 (deleted)
                                                P0005: ref!! 0003 (change from 5 to 4)
                                                P0006: ref!! 0003 (change from 6 to 5)
                                                P0007: ref!! 0003 (change from 7 to 6)

[BenjaBobs]

Seems also like the kind of thing json merge patch was created for, or for more advanced scenarios json patch.

Maybe an equivalent yaml syntax could be relevant?

[Kryptos-FR]

Your example is too simple. We support many more scenarios such as moving a child entity of a prefab (with all their components) while keeping the connection, removing the child entity of a prefab (with all their components) while keeping the connection, setting a value as overridable while it still has the same value as the parent prefab...

We went through a lot of iterations to have all features supported. So I believe the fact that we have to duplicate the values wasn't done without reason.

Before having that new format, we have to make sure that all current and desired features (even some that might be buggy) can be supported. It's not a trivial change. Unfortunately, I don't think we have the resources and time to rewrite the whole Prefab system, but you are welcome to do so. I just want to caution against hasty changes that are made for convenience.

[IXLLEGACYIXL]

https://discord.com/channels/500285081265635328/1181235782057476126/1199666973076881418
as im currently trying to think about an possible implementation in the new yamlserializer, when migrating to the new one we can "dump" all the old stuff as the migration uses the old serializer to the new one

any ideas and remarks are welcome

[xen2]

Another important reason is that you might edit the source prefab while an object using that prefab is not loaded (i.e. any game project using a prefab from a common package, and you edit the package itself).
We need the source object before it was changed (think of it like git, it can't diff using 2 objects, it needs a base as well).