Compatibility with Omniverse-style values in timeSamples

[staticx-g7]

Issue Description

When parsing USD files generated by ANARI-USD (uses omniverse API's), we encounter syntax like:
normal3f[] normals.timeSamples = { 0: None } in the usda file
TinyUSDZ throws errors here since it expects standard USD-compliant empty arrays ([]).

Current Workaround

We preprocess Omniverse USD files with:
fileContent = std::regex_replace(fileContent, std::regex("0: None"), "0: []");
This converts non-standard None to USD-compliant empty arrays.

Questions

1. Is this None syntax recognized as an Omniverse-specific extension or does tinyusdz handle these cases?
2. Would TinyUSDZ consider adding optional parsing for such cases for Omniverse USD Implementation?
3. Are there other Omniverse USD patterns we should handle similarly?

[syoyo]

You should attach minimal reproducible USD file and error message from 'tusdcat'

[staticx-g7]

---

Case 1: USD Empty Array Syntax

#usda 1.0

def Mesh "SimpleMesh"
{
    normal3f[] normals.timeSamples = { 0: [] }

    point3f[] points = [(0,0,0), (1,0,0), (0,1,0)]
    int[] faceVertexCounts = [3]
    int[] faceVertexIndices = [0, 1, 2]
}

Output from tusdcat for case 1: (Success)

[george2@jrlogin04 build]$ ./tusdcat minimal_repo.usda
#usda 1.0

def Mesh "SimpleMesh"
{
    point3f[] points = [(0, 0, 0), (1, 0, 0), (0, 1, 0)]
    normal3f[] normals.timeSamples = {
        0: [],
    }

    int[] faceVertexIndices = [0, 1, 2]
    int[] faceVertexCounts = [3]
}

---

---

Case 2: "None" Empty Syntax

#usda 1.0

def Mesh "SimpleMesh"
{
    normal3f[] normals.timeSamples = { 0: None }

    point3f[] points = [(0,0,0), (1,0,0), (0,1,0)]
    int[] faceVertexCounts = [3]
    int[] faceVertexIndices = [0, 1, 2]
}

Output from tusdcat for case 2: (Error)

ERR : Failed to parse USDA
[error]/p/home/jusers/george2/jureca/SDK/tinyusdz/src/usda-reader.cc:ReconstructPrim():1623 Failed to reconstruct Mesh Prim: [error]/p/home/jusers/george2/jureca/SDK/tinyusdz/src/prim-reconstruct.cc:ReconstructPrim<tinyusdz::GeomMesh>():3688 Parsing attribute `normals` failed. Error: Converting Attribute data failed. Maybe TimeSamples have values with different types?

[error]/p/home/jusers/george2/jureca/SDK/tinyusdz/src/usda-reader.cc:Read():1700 Parse failed:
err_stack[1] USDA source near line 10, col 1: [error]/p/home/jusers/george2/jureca/SDK/tinyusdz/src/ascii-parser.cc:Parse():5212 Failed to parse `def` block.
err_stack[0] USDA source near line 10, col 1: [error]/p/home/jusers/george2/jureca/SDK/tinyusdz/src/ascii-parser.cc:ParseBlock():5104 Constructing Prim type `Mesh` failed: Failed to reconstruct Prim: SimpleMesh


Failed to load USD file: minimal_repo.usda

---

---

I found similar examples of using None in time samples in the official USD documentation at https://openusd.org/release/api/_usd__page__value_clips.html. Specifically, in the section about handling missing values in clip sets, there's an example showing:

#usda 1.0 def "Model" { double a.timeSamples = { 2: None, 3: None } }

So is it a standard usd functionality? Anari usd uses OpenUSD

---

I have also attached the original usda file I was attempting with as a text file

vtk_actor__triangles_0_Geom_0.000000.txt

[syoyo]

@staticx-g7 Thank you!

The issue confirmed.

None in timeSamples is a valid syntax and at lest tinyusdz can parse it if it is a xform attibute.

https://github.com/lighttransport/tinyusdz/blob/dev/tests/usda/timesamples-none-000.usda

At least parsing USDA itself succeeds for your USDA. The issue exists in creating TimeSampled Attribute with None value for non-xform attributes.
Let me give time to investigate it.

[syoyo]

Created a fix: #233

Will be merged soon.

[staticx-g7]

Thank you so much 😄

[syoyo]

Now merged!