USDZExporter Issue

[CrystalDesignMT]

Description

When loading certain GLB's into the Google ModelViewer it show's the model correctly in the three.js viewport.

Only on iPhone the Model has flipped normals in AR.
Here QuickLook is used which needs USDZ files that are generated by converting the original glb trough the Three.js USDZExporter.
Issue on google/model-viewer
Reproduction Demo

Reproduction steps

1. Open the reproduction scene
2. Open the link of the preview on iPhone
3. Open the Model in AR

Code

https://glitch.com/edit/#!/boatneck-twisty-bellusaurus?path=index.html%3A40%3A0

Live example

• glitch

Screenshots

No response

Version

^0.154.0

Device

Mobile

Browser

Safari

OS

MacOS

[Mugen87]

When opening the glitch, I see the following alert:

There was an error starting the editor. Maybe try to reload?

Can you try to share one of your test glbs directly in this issue?

[CrystalDesignMT]

hm works for me, anyway here is the glb used in the demo:
https://gwcstoragedservices.blob.core.windows.net/diva3darchiv/quick_look_test.glb

[Mugen87]

I have imported the glTF asset into the three.js editor and then exported to USDZ. QuickLook indeed renders the model incorrectly. For comparison:

Editor:

QuickLook:

Something with the normals isn't right.

[Mugen87]

Sidenote: USDZLoader can properly load the file back so there must be a compatibility issue with QuickLook.

[WestLangley]

Something with the normals isn't right.

It does appear to be rendering back faces, which would imply a winding order issue.

[WestLangley]

In fact, the sample .glb file's hierarchy contains a node with a negative determinant -- i.e., the transform is a reflection matrix.

WebGLRenderer handles this gracefully by flipping the front face winding order.

[Mugen87]

So I guess the solution here is to fix the asset during the design phase so a negative determinant does not appear in the object hierarchy in the first place.

@CrystalDesignMT The idea is to remove the negative scale from the y-component from the second node of the object hierarchy. If you then reset the node's rotation as well, the asset looks like so in QuickLook:

Granted, the asset is mirrored but this should be fixed when you create the asset in your DCC tool. Just make sure you don't use negative scaling for that.