Normals issues with imported skinned model

[hybridherbst]

While importing the Apple Event usdz file, I noticed that the imported normals are broken / flipped at a certain point during the animation. This results in incorrect lighting and artifacts during the animation.

Note that there's a visible "flip" during the animation, and there's a noticeable seam in the normals:

Model link: https://github.com/Unity-Technologies/usd-unity-sdk/files/5218033/apple_event.usdz.zip

[jcowles]

Seems this model is a great stress test for corner cases -- we'll take a look.

Thanks for reporting!

[jcowles]

Are you sure this is a problem with normals? It looks like the real problem is we are not correctly importing the emissive color (at least for the built-in pipeline).

In the image below, the left side was the default import behavior and the right side I set manually by looking at the source USD file:

[jcowles]

This is what it looks like with my local emission fix (the color banding is coming from gif compression):

[jcowles]

@hybridherbst if you feel like there are additional bugs here, please reopen!

[jcowles]

Upon further inspection, I think there really are two different bugs here -- or at least, we should look into why the normals are funky (they may just be authored that way in the USD file)

[jcowles]

It looks like the authored normals are constant, which would only look correct in the rest position (note that this mesh is deformed by UsdSkel).

If I request Unity to recompute the normals, via advanced settings, they look correct.

@hybridherbst can you confirm?

[hybridherbst]

With "constant" you mean the mesh doesn't have any normals? Otherwise, shouldn't using UsdSkel also correctly transform them? Recomputing normals breaks continuity in most cases, and obviously removes the user-authored normals.

By the way, another model that exhibits a very similar looking normal deformation (without animations) on Unity side when importing is the Gramophone from the QuickLook gallery:
https://developer.apple.com/augmented-reality/quick-look/
If you import it it has a similar-looking normal rotation/flip thing going on near the neck that does not look that way in ARQL or other softwares.

[vickycl]

This appears to be fixed, thank you @lee-aandrew for testing :)