GLTFLoader, GLTFExporter: Remove KHR_materials_pbrSpecularGlossiness

[donmccurdy]

The Khronos Group archived the KHR_materials_pbrSpecularGlossiness extension ("no longer recommended for creating new files") about a year ago. I think it would be reasonable for us to remove support at this point, and focus efforts on the metal/rough workflow instead. All new and upcoming PBR features — volumetric refraction, iridescence, clearcoat, subsurface scattering, ... — are authored around the metal/rough model. With support for KHR_materials_ior and KHR_materials_specular, there is no particular advantage left to the spec/gloss model.

Existing spec/gloss models can be converted losslessly to metal/rough with:

npm install --global @gltf-transform/cli

gltf-transform metalrough in.glb out.glb

Related:

• GLTFLoader: Fix color space for specular map. #23630

Migration guide:

• Converting glTF PBR materials from spec/gloss to metal/rough

[donmccurdy]

/cc @takahirox

[takahirox]

I think it's ok to remove them. For users who still need the extension, we can provide the plugins at or somewhere else.

https://github.com/takahirox/three-gltf-extensions

[donmccurdy]

@elalish following up on #23630 (comment) — the web app https://gltf.report will now do the spec/gloss → metal/rough conversion automatically. The same conversion could be applied in other web-based tools, with:

import { WebIO } from '@gltf-transform/core';
import { KHRONOS_EXTENSIONS } from '@gltf-transform/extensions';
import { metalRough } from '@gltf-transform/functions';

const io = new WebIO().registerExtensions(KHRONOS_EXTENSIONS);

const document = await io.readBinary(byteArray);

// spec/gloss → metal/rough
await document.transform(metalRough());

const glb = await io.writeBinary(document);

[mrdoob]

I also think it's time 👍

[elalish]

SG, thanks @donmccurdy! Now I just need to remember to point people to that tool in our next release notes.

[donmccurdy]

Also, here's a migration guide for converting existing glTF files:

• Converting glTF PBR materials from spec/gloss to metal/rough

[takahirox]

It's good to add it to the Three.js migration guide? https://github.com/mrdoob/three.js/wiki/Migration-Guide

[donmccurdy]

Thanks, I'd missed that it covered r147 already — done!

[elalish]

@donmccurdy Does gltf-transform work in the browser so that I could add this conversion to our editor?

[donmccurdy]

@elalish the script above, #24950 (comment), will work in a browser, yes. 👍

What I'd do would be to load from the URL or DataTransfer API into glTF Transform, then export a GLB as Uint8Array, and to parse or load from a Blob URL in THREE.GLTFLoader from there. Happy to take questions in discussions as well!