usdview: rendering of flipped geometry looks incorrect

[hybridherbst]

Description of Issue

Looks like flipped geometry (e.g. scale -1,1,1) renders incorrectly in usdview. The spec says that winding order and lighting should be corrected, and some viewers (e.g. Storm in Omniverse) seem to respect this; however usdview does not.

Steps to Reproduce

1. Download
   NegativeScaleAndAlphaScale.usdz.zip
2. open with usdview
3. note that the 2nd and 3rd cubes display black

4. switch lighting to Dome
5. note that the 2nd and 3rd cube still look wrong, looks like flipped normals?

Expected (Storm in Omniverse looks good):

Discussion in usd-wg: https://academysoftwarefdn.slack.com/archives/C02TZPYMP8S/p1689118060187999

System Information (OS, Hardware)

Both Windows 11 and MacOS 13

Build Flags

On Windows: Omniverse usdview
On Mac: build without further options from latest dev

[spitzak]

cubes.zip

This might be a useful test file(s), feel free to add them to any public repository of usd tests. Contains cubes (with the top missing) with all combinations of single/doublesided, normals or no normals, left/right handed, and inverted/normal transformation. No renderer does these all correctly. There is also a version where all the cubes are instanced, which is even worse.

[spitzak]

Possibly-correct render from Storm of the non-instanced version

[jesschimein]

Filed as internal issue #USD-8497

[meshula]

These cube tests are great ~ and would make a lovely addition to https://github.com/usd-wg/assets/tree/main/test_assets !

To anyone not already on the aswf slack, there's related conversations going on here ~ https://join.slack.com/t/academysoftwarefdn/shared_invite/zt-1ygy120xu-CmzTocra0GYIxhxnGBwQOA

[spitzak]

Yes please add the tests to the free examples

[spitzak]

A shader with different front/back face colors would help as well, though I'm not sure if there is anything in UsdPreviewSurface

[spiffmon]

There is not. We were looking to MaterialX for a solution there, not sure if it has been deployed yet.

On Thu, Jul 13, 2023 at 9:49 AM Bill Spitzak ***@***.***> wrote: A shader with different front/back face colors would help as well, though I'm not sure if there is anything in UsdPreviewSurface — Reply to this email directly, view it on GitHub <#2536 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABPOU2FAYL3CR7KPMLJBHHLXQARIDANCNFSM6AAAAAA2H2XJBE> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

-- --spiffiPhone

[mnaehrig]

I'd like to point out that this is not a general problem with usdview. It depends on the platform. On Windows it also looks correct with usdview. On macOS it looks wrong. So I guess it has to do with the Metal backend. Still reproducable with OpenUSD 23.11.