GLTFLoader: Some glTF models cannot be cloned

[mikearmstrong001]

Description of the problem

GLTF2 models that are clones do not displayed correctly. This is for a number of reasons

• the onBeforeRender callback is not copied
• GLTFShader is not cloned across
• SkinnedModel skeleton is reinitialised to 0 bones and the source skinnedmodel skeleton is not cloned

http://jsfiddle.net/mn768h35/

Three.js version

• [X ] Dev
• r85
• ...

Browser

• All of them
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• Firefox
• Internet Explorer

OS

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• Windows
• macOS
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• Android
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Hardware Requirements (graphics card, VR Device, ...)

[Mugen87]

SkinnedModel skeleton is reinitialised to 0 bones and the source skinnedmodel skeleton is not cloned

Yeah, this is well known issue.

[mikearmstrong001]

Yeah, this is well known issue.

Is a solution being tracked ?
Is there a proposed solution to avoid having to re-parse the model from the downloaded file

While reparsing is reasonable for one off model download this would be problematic for many downloaded instances both in terms of memory and time.

[Mugen87]

The problem is currently discussed here #11574. We are trying to find a solution for this.

[donmccurdy]

Possible duplicate of #8869 (but thank you for the extra details and JSFiddle!)

Regarding onBeforeRender and GLTFShader, this only applies these apply to the KHR_materials_pbrSpecularGlossiness and KHR_technique_webgl extensions respectively. The spec for the latter is not final yet, so no one should be using that.

Models using the default PBR metal/rough and KHR_materials_common (blinn/phong) do not use GLTFShader or onBeforeRender, and can be cloned just fine. @mikearmstrong001 are you able to change your models from a spec/gloss to a metal/rough PBR workflow?

EDIT: or have i misunderstood? I don't see any cloning, or any GLTFShader objects, in the JSFiddle.

[mikearmstrong001]

EDIT: or have i misunderstood? I don't see any cloning, or any GLTFShader objects, in the JSFiddle.

? look for:

scene.add(gltf.scene.clone());

debugging led to knowing about the GLTFShader. The duck model does work

[mikearmstrong001]

Possible duplicate of #8869 (but thank you for the extra details and JSFiddle!)

I think so but I am unclear if that is related to the GLTFLoader or GLTF2Loader

Regarding GLTFShader and onBeforeRender, this only applies to the KHR_materials_pbrSpecularGlossiness and KHR_technique_webgl extensions. The spec for the latter is not final yet, so no one should be using that.

GLTFShaders are definitely created and the current design will not facilitate cloning as the details of the implementation are hidden. I did some workarounds to have my own version and may continue but I'd rather not introduce fragile code into the framework.

are you able to change your models from a spec/gloss to a metal/rough PBR workflow?

As this is for a framework built on three.js we can't stipulate the models used.

@mrdoob + others, any thoughts on making cloning a requirement as part of adding new model formats?

[donmccurdy]

Ok, if it helps the example you've included does not have any GLTFShaders, so once the animation issue is fixed you should be able to clone models fine.

gltf.scene.traverse((node) => {
  if (node.isMesh) console.log(node.material.type);
});
VM671:2 MeshStandardMaterial

As this is for a framework built on three.js we can't stipulate the models used.

Do you have a model showing the GLTFShader issue? There should not be any such models, because the KHR_technique_webgl extension has not been ratified for glTF2, and no exporters create it. GLTFShader is effectively dead code in the meantime.

Bear in mind that both spec-gloss and GLSL are optional extensions to the main glTF2 spec, and it's unlikely that three.js will support every possible extension. The only material type in the core specification is PBR metal-rough, or MeshStandardMaterial, and we support cloning that just fine. We also support cloning for common materials (MeshPhongMaterial) extension, although that spec is also not yet finalized.

I'll look into supporting cloning for KHR_materials_pbrSpecularGlossiness, but this is difficult without making changes to the core Mesh class. We'd need an onAfterClone callback or something, because the mesh can't reproduce its own onBeforeRender callback.

EDIT: I guess we could get away with child.onBeforeRender = this.onBeforeRender, if that seems safe? For spec-gloss.

[mikearmstrong001]

I was testing various meshes with CesiumMan so I think it probably just one of the pbr based examples eg

http://jsfiddle.net/b5r4cca4/

I guess we could get away with child.onBeforeRender = this.onBeforeRender, if that seems safe? For spec-gloss.

I'm not convinced this would work as the uniforms would reference the original hierarchy.

The way I looked into handling it was as a post cloning fixup that worked over the hierarchy mapping source nodes to cloned nodes based. Something similar could be done by specialise the clone on the base scene, I agree the current clone setup is too restrictive because it is difficult to operate on global aspects of the scene in one pass and perhaps by relaxing this it will simplify the skeleton cloning as well.

[donmccurdy]

Addressing comments from @zellski and @jbaicoianu in #11574 —

It sounds like, in addition to the ongoing work on shared Skeleton, GLTF2Loader should avoid referencing UUIDs for skinning. It will be necessary to add names to unnamed bones in the loader, but that's a reasonable trade to support cloning and serialization.

[mrdoob]

@cdata just hacked this for a project he's working on:
https://gist.github.com/cdata/f2d7a6ccdec071839bc1954c32595e87