USDZExporter does not work with MeshoptDecoder

[wallabyway]

There's an error when USDZExporter encodes a USDZ file based on a GLTF compressed with MeshOpt compression.

For example,
if I compress cube.glb with MeshOpt (gltfpack -I cube.glb -o cube.zeux.glb), then will preview correctly inside three.js.
When I click the AR button, it causes the following error.

and the error refers to

line 291:

array.push( `(${ data[ i + 0 ].toPrecision( PRECISION ) }, ${ data[ i + 1 ].toPrecision( PRECISION ) }, ${ data[ i + 2 ].toPrecision( PRECISION ) })` );

To Reproduce

Steps to reproduce the behavior:

1. Compress cube.glb or damaged-helmet.glb with gltfpack -I cube.glb -o cube.zeux.glb
2. Load the glb using

			import { MeshoptDecoder } from 'https://wallabyway.github.io/gltf-imaginate-test/jsm/meshopt_decoder.module.js';

...
				const loader = new GLTFLoader().setPath( 'glb/' );
				loader.setMeshoptDecoder(MeshoptDecoder);
				loader.load( 'output.glb', async function ( gltf ) {

3. Host and Open index.html on iPhone, and click on 'AR' button
4. Host and Open index.html on desktop browser, and click on 'AR' button, and refer to error in debug console.

Live example

• jsfiddle-dev

Expected behavior

Expect the compressed .glb to appear in Quicklook

Screenshots

Platform:

• Browser: [Chrome]
• Three.js version: [latest]

[donmccurdy]

The issue here is that USDZExporter accesses attribute.array on vertex attributes, which won't work for geometry with interleaved attributes:

three.js/examples/jsm/exporters/USDZExporter.js

Lines 287 to 293 in 0a5fa7b

	const data = attribute.array;
	for ( let i = 0; i < data.length; i += 3 ) {
	array.push( `(${ data[ i + 0 ].toPrecision( PRECISION ) }, ${ data[ i + 1 ].toPrecision( PRECISION ) }, ${ data[ i + 2 ].toPrecision( PRECISION ) })` );
	}

Using attribute.getXYZ( ... ) instead should work fine. Also note that the vertex attributes will likely be normalized, I'm not sure whether USDZExporter accounts for this. You can recreate the same error with these models and the three.js editor:

Archive.zip

^One model is interleaved, the other is not. Neither uses compression, and only the interleaved copy will have errors. Normalization and compression will be lost when converting to USDZ, so file size will probably increase.

[wallabyway]

That fixed it - thanks !
Loads very quickly.
https://github.com/wallabyway/quicklook-example