Support for glTF 2.0

[donmccurdy]

• glTF 1.1 will be 2.0: glTF 1.1 will be 2.0! KhronosGroup/glTF#817
• glTF 2.0 draft: glTF 2.0 draft KhronosGroup/glTF#826
• Sample models: https://github.com/cx20/gltf-test/tree/2.0

Core changes:

• Create GLTF2Loader.
• Add PBR materials.
  • Metallic-Roughness.
  • Specular-Glossiness.
• Add morph targets.
• Add image.bufferView so that textures/geometry/keyframes can be stored in one binary blob if desired.
• Replace top-level glTF object properties that are currently accessed by property name, e.g., the accessors object, with arrays that are accessed by index.
• Nodes allow only 1 node.mesh, not node.meshes array.

Extension changes:

• KHR_binary_glTF extension is moved into core spec.
• KHR_common_materials extension no longer includes lights.
• KHR_lights extension.
• KHR_technique_webgl for GLSL. GLSL is no longer part of core spec.

I'm probably missing some things, there is a more exhaustive list: Spec changes from 1.0 to 2.0. This will settle over the coming weeks.

/cc @pjcozzi @takahirox

[donmccurdy]

There may be some breaking changes here... @mrdoob @takahirox is it best to keep work on a branch until we're at least able to support features from v1.0 when loading files of v2.0 format?

[mrdoob]

Considering that there aren't that many files out there yet... Would make sense to do a new GLTF2Loader that only supports 2.0 and keep the code clean?

[takahirox]

gltf.asset.version is a required property in glTF.

https://github.com/KhronosGroup/glTF/tree/master/specification/1.0#asset

Branching some logics depending on the version would be another option
if we can keep the code clean?

UPDATE:
gltf.asset is not a required property so there'd be files not including gltf.asset.version.
https://github.com/KhronosGroup/glTF/tree/master/specification/1.0#gltfasset

UPDATE2:
gltf.asset is a required property in 2.0.
https://github.com/KhronosGroup/glTF/tree/2.0/specification/2.0#gltfasset-white_check_mark
So if gltf.asset doesn't exist in .gltf file, we can detect it's 1.0.

[donmccurdy]

Well the good news is, GLTFLoader already supports most of the existing 2.0 sample models. The only exception I see is the glTF-MaterialsCommon versions, which will need changes, and I don't have any samples of those models yet.

Since a lot of the 2.0 changes involve logic going from extension A to extension B, or to/from the core spec, branching within one loader sounds a little unpleasant. If we split into GLTFLoader and GLTF2Loader, how long would we keep the first around? If we're OK with removing that after a few releases (say, r86?) then I'd vote to make the split. If we think we want to actively maintain both for a while, then let's try to keep them in one loader.

Or possible middle ground, we could drop support for 1.0 extensions (lights in common_materials, binary_gltf extension) in favor of their 2.0 counterparts, but try to keep compatibility with core 1.0 for now.

[mrdoob]

I would vote for forking to GLTF2Loader, and encourage people to export to 2.0. Eventually removing the first version.

[donmccurdy]

Sounds reasonable to me.

@takahirox The key thing is probably converters. Once collada2gltf and obj2gltf provide glTF2.0, use of 1.0 will taper off, and that's when we can consider dropping the first version. It would be great to use gltf.asset.version to trigger a warning like For glTF <2.0, use THREE.GLTFLoader r85.

[takahirox]

OK, that sounds good to me.

Just what I concerned was if 1.0 keeps being used or not.
If converters will deprecate 1.0 support, we don't need to take care of 1.0.

Just in case, I'm asking @pjcozzi about their opinion.
https://twitter.com/superhoge/status/831719215727992834

[takahirox]

Anyways, let's start with making GLTF2Loader.
We can choose merging or replacing later.

BTW I received the answer from @pjcozzi .
https://twitter.com/pjcozzi/status/832394717119782912

we have no plans to deprecate 1.0, but we are encouraging exporters, converters, and runtimes to upgrade to 2.0.
Cesium's approach (still in progress) is to convert 1.0 to 2.0 on the fly using gltf-pipeline,
https://github.com/AnalyticalGraphicsInc/gltf-pipeline

[donmccurdy]

Yay! I will start a clean copy now unless you've started someplace. :)

EDIT: #10816

[donmccurdy]

@takahirox FYI I'm working on the .GLB changes now (and attempting to keep the checklist above up to date).

[takahirox]

FYI I'm working on Specular-Glossiness.

[takahirox]

Done Specular-Glossiness.
Maybe I'll work on KHR_technique_webgl extension next...

[cx20]

I am testing glTF 2.0 sample models and Three.js glTF 2.0 Loader.
https://github.com/cx20/gltf-test/tree/2.0#gltf-20-pbr-models

However, it seems that some PBR models are not displayed properly.
https://cdn.rawgit.com/cx20/gltf-test/b6900f6f4d755a71691aaef5a19279da7472b69f/examples/threejs/index.html?category=tutorialModels&model=Corset&scale=1&type=glTF

I think that it was caused by updating to the latest specification about 10 days ago.
https://github.com/KhronosGroup/glTF-Sample-Models/tree/master/2.0/Corset