How to get a bone's weight using a json file - gltf

Question

I am trying to get the weight for every bone using a gltf json file but i dont know how
here is the json file i am trying to get the weight from:
{
"accessors": [
{
"bufferView": 0,
"componentType": 5126,
"count": 317,
"max": [
10.570027351379395,
15.918471336364746,
6.125584125518799
],
"min": [
-2.611180305480957,
-1.9711413383483887,
-7.055622577667236
],
"type": "VEC3"
},
{
"bufferView": 1,
"componentType": 5126,
"count": 317,
"type": "VEC3"
},
{
"bufferView": 2,
"componentType": 5126,
"count": 317,
"type": "VEC2"
},
{
"bufferView": 3,
"componentType": 5121,
"count": 317,
"type": "VEC4"
},
{
"bufferView": 4,
"componentType": 5126,
"count": 317,
"type": "VEC4"
},
{
"bufferView": 5,
"componentType": 5123,
"count": 768,
"type": "SCALAR"
},
{
"bufferView": 6,
"componentType": 5126,
"count": 5,
"type": "MAT4"
}
],
"asset": {
"generator": "Khronos glTF Blender I/O v1.5.17",
"version": "2.0"
},
"bufferViews": [
{
"buffer": 0,
"byteLength": 3804,
"byteOffset": 0
},
{
"buffer": 0,
"byteLength": 3804,
"byteOffset": 3804
},
{
"buffer": 0,
"byteLength": 2536,
"byteOffset": 7608
},
{
"buffer": 0,
"byteLength": 1268,
"byteOffset": 10144
},
{
"buffer": 0,
"byteLength": 5072,
"byteOffset": 11412
},
{
"buffer": 0,
"byteLength": 1536,
"byteOffset": 16484
},
{
"buffer": 0,
"byteLength": 320,
"byteOffset": 18020
}
],
"buffers": [
{
"byteLength": 18340,
"uri": "manoe.bin"
}
],
"images": [
{
"mimeType": "image/png",
"name": "Material_002_baseColor",
"uri": "Material_002_baseColor.png"
}
],
"materials": [
{
"doubleSided": true,
"name": "Material.001",
"pbrMetallicRoughness": {
"baseColorTexture": {
"index": 0
},
"metallicFactor": 0,
"roughnessFactor": 0.4000000059604645
}
}
],
"meshes": [
{
"name": "Cone.001",
"primitives": [
{
"attributes": {
"JOINTS_0": 3,
"NORMAL": 1,
"POSITION": 0,
"TEXCOORD_0": 2,
"WEIGHTS_0": 4
},
"indices": 5,
"material": 0
}
]
}
],
"nodes": [
{
"name": "Bone.004",
"rotation": [
0.17750653624534607,
-2.8648443617385055e-8,
-0.9102426171302795,
0.37409862875938416
],
"scale": [
1.000000238418579,
1,
1
],
"translation": [
-4.411018750261064e-8,
0.8281745314598083,
1.4894996525072202e-7
]
},
{
"children": [
0
],
"name": "Bone.002",
"rotation": [
0.2184765785932541,
-0.2617807984352112,
-0.7560504078865051,
0.558682918548584
],
"scale": [
1.0000003576278687,
1,
1
],
"translation": [
6.093483762015239e-8,
0.8281747698783875,
-1.283853023892334e-9
]
},
{
"name": "Bone.003",
"rotation": [
-0.4916436970233917,
7.804754176277129e-8,
-0.14189021289348602,
0.8591586947441101
],
"scale": [
1,
1.0000001192092896,
0.9999999403953552
],
"translation": [
-2.4224684125329077e-7,
0.8281750679016113,
-2.68131650216219e-9
]
},
{
"children": [
1,
2
],
"name": "Bone.001",
"rotation": [
-0.11594496667385101,
0.08448944985866547,
-0.5036448836326599,
0.8519155383110046
],
"scale": [
1.000000238418579,
0.9999995827674866,
1
],
"translation": [
-1.357730283757519e-8,
1.0000007152557373,
-3.471412068391244e-14
]
},
{
"children": [
3
],
"name": "Bone",
"rotation": [
2.3709270635663415e-7,
2.8494374859633353e-8,
6.9593789722201e-15,
1
],
"scale": null,
"translation": null
},
{
"mesh": 0,
"name": "Cone.001",
"skin": 0
},
{
"children": [
5,
4
],
"name": "ArmatureBase",
"scale": [
5.400000095367432,
5.400000095367432,
5.400000095367432
]
}
],
"samplers": [
{
"magFilter": 9729,
"minFilter": 9987
}
],
"scene": 0,
"scenes": [
{
"name": "Scene",
"nodes": [
6
]
}
],
"skins": [
{
"inverseBindMatrices": 6,
"joints": [
4,
3,
1,
0,
2
],
"name": "ArmatureBase"
}
],
"textures": [
{
"sampler": 0,
"source": 0
}
]
}

Answer 1

The glTF overview card summarizes it nicely:
Every vertex can be associated with up to 4 joints, each with a given weight.
These are encoded in the components of the JOINTS_0 and WEIGHTS_0 accessors. In your case those are accessors 3 and 4 and bufferviews 3 and 4 with a component type of byte and float, respectively.
One more indirection into the bufferViews component here tells you where in the binary file to look.