Incompatible with KHR_materials_variants?

[echadwick-artist]

Compressing a model with variants seems to create a malformed output file?

Starting with the GLB from here: https://github.com/KhronosGroup/glTF-Sample-Models/blob/master/2.0/SheenChair/README.md

gltf-pipeline -i SheenChair.glb -o SheenChair-draco.glb -d

Babylon.js sandbox fails to load the output, with this error:

#/materials/: Failed to find index (4)

glTF Validator says this:

{
"uri": "SheenChair-draco.glb",
"mimeType": "model/gltf-binary",
"validatorVersion": "2.0.0-dev.3.3",
"validatedAt": "2021-01-04T21:11:02.049Z",
"issues": {
"numErrors": 0,
"numWarnings": 2,
"numInfos": 5,
"numHints": 0,
"messages": [
{
"code": "UNSUPPORTED_EXTENSION",
"message": "Cannot validate an extension as it is not supported by the validator: 'KHR_materials_variants'.",
"severity": 1,
"pointer": "/extensionsUsed/2"
},
{
"code": "UNSUPPORTED_EXTENSION",
"message": "Cannot validate an extension as it is not supported by the validator: 'KHR_draco_mesh_compression'.",
"severity": 1,
"pointer": "/extensionsUsed/3"
},
{
"code": "UNUSED_OBJECT",
"message": "This object may be unused.",
"severity": 2,
"pointer": "/meshes/2/primitives/0/attributes/TEXCOORD_0"
},
{
"code": "UNUSED_OBJECT",
"message": "This object may be unused.",
"severity": 2,
"pointer": "/bufferViews/0"
},
{
"code": "UNUSED_OBJECT",
"message": "This object may be unused.",
"severity": 2,
"pointer": "/bufferViews/1"
},
{
"code": "UNUSED_OBJECT",
"message": "This object may be unused.",
"severity": 2,
"pointer": "/bufferViews/2"
},
{
"code": "UNUSED_OBJECT",
"message": "This object may be unused.",
"severity": 2,
"pointer": "/bufferViews/3"
}
],
"truncated": false
},
"info": {
"version": "2.0",
"generator": "babylon.js glTF exporter for 3dsmax 2020 v20201123.8, then manually edited to add Sheen and Variants",
"extensionsUsed": [
"KHR_texture_transform",
"KHR_materials_sheen",
"KHR_materials_variants",
"KHR_draco_mesh_compression"
],
"extensionsRequired": [
"KHR_texture_transform",
"KHR_draco_mesh_compression"
],
"resources": [
{
"pointer": "/buffers/0",
"mimeType": "application/gltf-buffer",
"storage": "glb",
"byteLength": 3201444
},
{
"pointer": "/images/0",
"mimeType": "image/png",
"storage": "buffer-view",
"image": {
"width": 1024,
"height": 1024,
"format": "rgb",
"primaries": "srgb",
"transfer": "srgb",
"bits": 8
}
},
{
"pointer": "/images/1",
"mimeType": "image/png",
"storage": "buffer-view",
"image": {
"width": 512,
"height": 512,
"format": "rgb",
"primaries": "srgb",
"transfer": "srgb",
"bits": 8
}
},
{
"pointer": "/images/2",
"mimeType": "image/png",
"storage": "buffer-view",
"image": {
"width": 512,
"height": 512,
"format": "rgb",
"primaries": "srgb",
"transfer": "srgb",
"bits": 8
}
},
{
"pointer": "/images/3",
"mimeType": "image/png",
"storage": "buffer-view",
"image": {
"width": 512,
"height": 512,
"format": "rgb",
"primaries": "srgb",
"transfer": "srgb",
"bits": 8
}
},
{
"pointer": "/images/4",
"mimeType": "image/png",
"storage": "buffer-view",
"image": {
"width": 512,
"height": 512,
"format": "rgb",
"primaries": "srgb",
"transfer": "srgb",
"bits": 8
}
},
{
"pointer": "/images/5",
"mimeType": "image/png",
"storage": "buffer-view",
"image": {
"width": 1024,
"height": 512,
"format": "rgb",
"primaries": "srgb",
"transfer": "srgb",
"bits": 8
}
}
],
"animationCount": 0,
"materialCount": 4,
"hasMorphTargets": false,
"hasSkins": false,
"hasTextures": true,
"hasDefaultScene": true,
"drawCallCount": 4,
"totalVertexCount": 22459,
"totalTriangleCount": 39936,
"maxUVs": 2,
"maxInfluences": 0,
"maxAttributes": 4
}
}