Extra Nodes get Created per object in a glb

[johanos]

When models are getting imported their hierarchy is getting created like above.
where the water bottle only defines one submesh called water bottle

So instead of loading the gltf like we do know.

WaterBottle
    -WaterBottleEmptyNode
        -WaterBottleMesh

we should do this

WaterBottle
    -WaterBottleMesh

because to access the materials of these nodes, we right now have to do something like

node.childNodes[0].childNodes[0].geometry?.firstMaterial

[magicien]

I mapped each node/mesh/primitive onto SCNNode, so WaterBottleEmptyNode is mapped onto mesh.
Actually, mesh SCNNode doesn't have any 3D data. It has only 'name'.
It's possible to omit mesh nodes, but it could be confusing if child nodes and primitive nodes are in the same layer.

How do you think?

[johanos]

What do you mean exactly?

From what I understand the primitives are part of the mesh object. which point to indices and materials. but mesh[0] defines a mesh with geometry and materials. so I see it more confusing to interpret that as

WaterBottle                     -- start of gltf asset
    -WaterBottleEmptyNode       -- mesh[0] object, but its an empty container
        -WaterBottleMesh        -- primitives of mesh[0], contains Normal, UV, Position, Tangent info

than

WaterBottle                      -- start of gltf asset
    -WaterBottleMesh             -- mesh[0] object, + primitives: UV, Normal, Position, Tangent info.

SCNNode is capable of having the format be this way and it would be less confusing to work with the nodes this way

here's a screenshot of the babylon js inspector ( __root would be what we are calling WaterBottle) and then the only child node is WaterBottle.

edit: and the child nodes of these meshes could just be children of the base mesh

WaterBottle                      -- start of gltf asset
    -WaterBottleMesh             -- mesh[0] object, + primitives: UV, Normal, Position, Tangent info.
        -WaterBottleChild1
    -WaterBottleSiblingNode

[magicien]

Thank you for your explanation!

Current mapping between glTF and SceneKit looks like this:

I don't think I can change the mapping into this way because SCNNode can have only one geometry. I'm not sure, but I think if SCNGeometry has 2 or more vertex SCNGeometrySources, SceneKit will use only the first source.

This is possible, but I'm worried about putting primitives and children nodes in the same layer could be confusing.

[ryancrunchi]

This should be in the readme as technical documentation.

[digitallysavvy]

Bump on this issue because I ran into problems with the node hierarchy.

The issue with the extra nodes is the duplication of names and it forces the developer to write a nasty work-around.

The issue really becomes apparent when you use the childNodeWithName because the method returns the first instance of a node with this name, but with the given hierarchy that node is not the one I'm looking for but instead an arbitrary parent. To get the node I am looking for I then have to call childNodeWithName again and then use childNodes.first to get the node with the geometry I wish to affect.

This is a headache for anyone trying to do anything as simple as change a material.

I have opened a PR (#37) that addresses this issue.

@magicien I know you have some reservations about changing this structure so I'd like to find a resolution that works for all because as the current version stands this is a major hinderance to simple traversals for named nodes.

[digitallysavvy]

Given its been almost a year since this issue has been opened without much response from @magicien ... whomever else is running into this issue, please check out my fork. I fixed the node structure issue. In the fork below, the scene graph in SceneKit is a 1:1 match of the structure of the GLB and doesn't distort the scene hierarchy with arbitrary nodes in the way this library does.

https://github.com/digitallysavvy/GLTFSceneKit