How to handle "Skipping Draco compression on non-indexed primitive"

[marcofugaro]

Is your feature request related to a problem? Please describe.

Hi, I am using the JS api of the draco encoder in conjunction with the three.js' GLTFExporter like this:

import { WebIO } from '@gltf-transform/core';
import { KHRONOS_EXTENSIONS, DracoMeshCompression } from '@gltf-transform/extensions';

const io = new WebIO()
  .registerExtensions(KHRONOS_EXTENSIONS)
  .registerDependencies({
    'draco3d.encoder': await new DracoEncoderModule(),
  });

new GLTFExporter().parse(scene, (gltf) => {
  const document = io.readJSON({
    json: gltf,
    resources: {}, 
  });

  document.createExtension(DracoMeshCompression)
    .setRequired(true)

  const { json: compressedGltf } = io.writeJSON(document);
});

Whenever I run this code, it logs this:

And the gltf is of course not compressed.

The input geometry looks like this, as you can see it's a non-indexed geometry.

I can provide an executable example if needed.

Describe the solution you'd like
Any way to make it work with non-indexed geometries?

Additional context
Related to this mrdoob/three.js#22227 (comment)

[donmccurdy]

The primitive needs to be indexed for compression, and that isn't done automatically because it's generally lossy... You can do this manually with the weld function though:

import { weld } from '@gltf-transform/functions';

await document.transform(weld({tolerance: 0.0001}));

const glb = io.writeBinary(document);

---

const { json: compressedGltf } = io.writeJSON(document);

Note that resources are returned here as well; if you need a single file it's best to write to a binary GLB.

[marcofugaro]

Thanks! It worked