SceneKit issues on iOS

[lanxinger]

Just wanted you to also be aware that currently the output doesn't render properly with the latest SceneKit framework on iOS/iPadOS and VisionOS.

It is displaying correctly everywhere else other than SceneKit.

I have reported this to Apple under FB15101924. So far no response on the ticket but it continues to be a problem on iOS 18.1 beta 6.

SceneKit Render:

Preview:

RealityView (which is a new swiftUI based renderer) inside Xcode:

Xcode import:

usdchecker:

Modelfile (rename to .usdz since it's not allowed on github):
model.zip

[pablode]

Thanks for the report!

[lanxinger]

@pablode So it seems that there is a metallic map getting assigned during the conversion.

I opened the model with Reality Convert on macOS and you can see the metallic slot being assigned with the roughness map.

I am not sure if this assigment is intended or a mistake during the conversion process as there was no metalness property defined in the source gltf model.

[pablode]

Interesting. Going to do a code review. Can you provide me with the source glTF file?

[lanxinger]

Thank you @pablode

here is the .glb zipped up since github doesn't accept it directly:
link.zip

I see in blender the model does have a metallic map assigned but the factor is set to 0 rendering it non metallic:

[pablode]

According to the glTF spec, the metallic factor is multiplied with the texture values. This is done in UsdPreviewSurface using the UsdUVTexture scale input. It seems SceneKit just ignores this input. This is why the other renderers work.

I guess one optimization would be to drop the texture. However, I think this should be done by in advance by gltf-transform rather than in the converter.

[lanxinger]

thank you @pablode . Yes I think the easiest would be to write a small script for gltf-transform and remove the metallic texture node entirely before running the conversion with guc. Appreciate all the help on this!