Add EXT_meshopt_compression support

[donmccurdy]

See mrdoob/three.js#21114.

[zeux]

Out of curiosity, would something like this zeux/meshoptimizer#232 be of interest here, or is copying the decoder .js a natural/expected route to follow for three.js?

[donmccurdy]

Thanks for checking — I don't think it makes much difference for this viewer, since three.js is already a dependency and I have the option of copying the decoder into this repository's Git tree or importing from the three.js npm package. I just haven't gotten to it yet.

A separate npm package for the meshoptimizer decoder could be helpful for donmccurdy/glTF-Transform#106, though, since it doesn't already depend on three.js. That would allow glTF-Transform to decompress a glTF file using KHR_meshopt_compression to a vanilla glTF file. The workflow for reading files using Draco, for example, is...

import { NodeIO } from '@gltf-transform/core';
import { DracoMeshCompression } from '@gltf-transform/extensions';

import * as draco3d from 'draco3dgltf';

const io = new NodeIO()
  .registerExtensions([DracoMeshCompression])
  .registerDependencies({
    'draco3d.decoder': await draco3d.createDecoderModule(), // Optional.
    'draco3d.encoder': await draco3d.createEncoderModule(), // Optional.
  });

const doc = io.read('compressed.glb');

... which allows me to leave those dependencies out of the library itself, while still making it easy for users to enable them.