Flattened .usdz

[CedricGuillemet]

I'm testing Tinyusdz with Babylon.js.
BabylonJS/Babylon.js#16005
Not supporting multiple usd files inside the usdz (or flattened) is an issue.
Is it something that can be addressed easily (no pressure!)
Is it part of your roadmap?

[syoyo]

You should describe the issue in detail with reproducible file and codes.

[CedricGuillemet]

The .usdz produced by these playgrounds can't be imported with the wasm build of Tinyusdz:

https://playground.babylonjs.com/#H2G5XW#3
https://playground.babylonjs.com/#H2G5XW#4
https://playground.babylonjs.com/#5N3RWK#1

the extracted .usd can be loaded by Tinyusdz when --flatten command line parameter is set. But flattening usdz seems to be not entirely supported (

tinyusdz/examples/tusdcat/main.cc

Line 144 in db6cad0

std::cout << "--flatten is ignored for USDZ at the moment.\n";

)

[syoyo]

USD composition(flattening) feature in TinyUSDZ is work-in-progress, but at least it should work for basic USD compisition.

Composition is disabled a.t.m for USDZ to avoid the potential risk of composition in native(C++) environment(e.g. infinite recursion, memory overflow, etc.). We need more tests and code improvements to make USD composition implementation in TinyUSDZ robust and secure.

But if we use TinyUSDZ through WASM, this limitation can be relaxed, since WASM layer itself will do nice job for security.

So you can contribute enabling flattening feature for USDZ model when the code is beging compiled for WASM(__EMSCRIPTEN__).

PR is much appreciated!(As you know, please see tusdcat source code to how to do flattening)