Draco Compression Issue with EXT_instance_features and EXT_mesh_gpu_instancing Extensions

[lanvada]

Hello,

I encountered an issue while using Draco's compression feature on a GLB file that utilizes the EXT_instance_features and EXT_mesh_gpu_instancing extensions. After compression, the resulting file appears to be corrupted.

It seems that the buffer view responsible for GPU instancing has been removed in the compressed file's JSON. This removal breaks the model's ability to load correctly and fails format validation checks.

Could you please look into this issue? Any help or guidance on how to address this problem would be greatly appreciated.

Thank you!

Below are the JSON sections of the GLB files before and after compression.

• JSON before compression:

{
  "asset": { "generator": "Smhc.Graphics.Gltf@1.2.3.9", "version": "2.0" },
  "scene": 0,
  "scenes": [
    {
      "name": "root scene",
      "nodes": [0],
      "extras": {
        "name": "rac_basic_sample_project",
        "isBIMModel": "true",
        "modelGuid": "f2415188-5743-41f7-9117-8b195905cb43"
      }
    }
  ],
  "nodes": [
    { "name": "root", "children": [1] },
    { "name": "instanced", "children": [2, 3] },
    {
      "name": "705e25a1-127e-4d76-b5f5-4e766ef073a3-000f1bef",
      "mesh": 0,
      "extensions": {
        "EXT_mesh_gpu_instancing": {
          "attributes": {
            "TRANSLATION": 6,
            "ROTATION": 7,
            "SCALE": 8,
            "_FEATURE_ID_0": 9
          }
        },
        "EXT_instance_features": {
          "featureIds": [{ "featureCount": 4, "attribute": 0 }]
        }
      }
    },
    {
      "name": "705e25a1-127e-4d76-b5f5-4e766ef073a3-000f1d9e",
      "mesh": 1,
      "extensions": {
        "EXT_mesh_gpu_instancing": {
          "attributes": {
            "TRANSLATION": 10,
            "ROTATION": 11,
            "SCALE": 12,
            "_FEATURE_ID_0": 13
          }
        },
        "EXT_instance_features": {
          "featureIds": [{ "featureCount": 4, "attribute": 0 }]
        }
      }
    }
  ],
  "meshes": [
    {
      "name": "SM_Dining Chair (3)",
      "primitives": [
        {
          "attributes": { "POSITION": 0, "NORMAL": 1 },
          "indices": 2,
          "material": 0
        }
      ]
    },
    {
      "name": "SM_Dining Chair (3)",
      "primitives": [
        {
          "attributes": { "POSITION": 3, "NORMAL": 4 },
          "indices": 5,
          "material": 0
        }
      ]
    }
  ],
  "accessors": [
    {
      "bufferView": 0,
      "byteOffset": 0,
      "componentType": 5126,
      "count": 4766,
      "type": "VEC3",
      "max": [0.4006734, 0.7755031, 0.4090699],
      "min": [-0.006043643, -0.0006093467, -0.0308729019]
    },
    {
      "bufferView": 1,
      "byteOffset": 0,
      "componentType": 5126,
      "count": 4766,
      "type": "VEC3",
      "max": [1.0, 1.0, 0.9998036],
      "min": [-1.0, -1.0, -0.9998036]
    },
    {
      "bufferView": 2,
      "byteOffset": 0,
      "componentType": 5123,
      "count": 23328,
      "type": "SCALAR"
    },
    {
      "bufferView": 3,
      "byteOffset": 0,
      "componentType": 5126,
      "count": 4766,
      "type": "VEC3",
      "max": [0.4006734, 0.7755031, 0.4090699],
      "min": [-0.006043643, -0.0006093467, -0.0308729019]
    },
    {
      "bufferView": 4,
      "byteOffset": 0,
      "componentType": 5126,
      "count": 4766,
      "type": "VEC3",
      "max": [1.0, 1.0, 0.9998036],
      "min": [-1.0, -1.0, -0.9998036]
    },
    {
      "bufferView": 5,
      "byteOffset": 0,
      "componentType": 5123,
      "count": 23328,
      "type": "SCALAR"
    },
    {
      "bufferView": 6,
      "byteOffset": 0,
      "componentType": 5126,
      "count": 4,
      "type": "VEC3"
    },
    {
      "bufferView": 7,
      "byteOffset": 0,
      "componentType": 5126,
      "count": 4,
      "type": "VEC4"
    },
    {
      "bufferView": 8,
      "byteOffset": 0,
      "componentType": 5126,
      "count": 4,
      "type": "VEC3"
    },
    {
      "bufferView": 9,
      "byteOffset": 0,
      "componentType": 5126,
      "count": 4,
      "type": "SCALAR"
    },
    {
      "bufferView": 10,
      "byteOffset": 0,
      "componentType": 5126,
      "count": 4,
      "type": "VEC3"
    },
    {
      "bufferView": 11,
      "byteOffset": 0,
      "componentType": 5126,
      "count": 4,
      "type": "VEC4"
    },
    {
      "bufferView": 12,
      "byteOffset": 0,
      "componentType": 5126,
      "count": 4,
      "type": "VEC3"
    },
    {
      "bufferView": 13,
      "byteOffset": 0,
      "componentType": 5126,
      "count": 4,
      "type": "SCALAR"
    }
  ],
  "bufferViews": [
    {
      "byteOffset": 0,
      "buffer": 0,
      "byteLength": 57192,
      "byteStride": 12,
      "target": 34962
    },
    {
      "byteOffset": 57192,
      "buffer": 0,
      "byteLength": 57192,
      "byteStride": 12,
      "target": 34962
    },
    { "byteOffset": 114384, "buffer": 0, "byteLength": 46656, "target": 34963 },
    {
      "byteOffset": 161040,
      "buffer": 0,
      "byteLength": 57192,
      "byteStride": 12,
      "target": 34962
    },
    {
      "byteOffset": 218232,
      "buffer": 0,
      "byteLength": 57192,
      "byteStride": 12,
      "target": 34962
    },
    { "byteOffset": 275424, "buffer": 0, "byteLength": 46656, "target": 34963 },
    { "byteOffset": 322080, "buffer": 0, "byteLength": 48, "byteStride": 12 },
    { "byteOffset": 322128, "buffer": 0, "byteLength": 64, "byteStride": 16 },
    { "byteOffset": 322192, "buffer": 0, "byteLength": 48, "byteStride": 12 },
    { "byteOffset": 322240, "buffer": 0, "byteLength": 16, "byteStride": 4 },
    { "byteOffset": 322256, "buffer": 0, "byteLength": 48, "byteStride": 12 },
    { "byteOffset": 322304, "buffer": 0, "byteLength": 64, "byteStride": 16 },
    { "byteOffset": 322368, "buffer": 0, "byteLength": 48, "byteStride": 12 },
    { "byteOffset": 322416, "buffer": 0, "byteLength": 16, "byteStride": 4 }
  ],
  "materials": [
    {
      "name": "M_Phase - Exist",
      "pbrMetallicRoughness": {
        "baseColorFactor": [0.498039216, 0.498039216, 0.498039216, 1.0],
        "metallicFactor": 0.0,
        "roughnessFactor": 0.609375
      },
      "doubleSided": true
    }
  ],
  "buffers": [
    { "name": "53056330-2811-4816-84ba-b5022378e0d3", "byteLength": 322432 }
  ],
  "extensionsUsed": ["EXT_mesh_gpu_instancing", "EXT_instance_features"],
  "extensionsRequired": ["EXT_mesh_gpu_instancing"]
}

• JSON after compression:

{
  "asset": { "generator": "Smhc.Graphics.Gltf@1.2.3.9", "version": "2.0" },
  "scene": 0,
  "scenes": [
    {
      "name": "root scene",
      "nodes": [0],
      "extras": {
        "name": "rac_basic_sample_project",
        "isBIMModel": "true",
        "modelGuid": "f2415188-5743-41f7-9117-8b195905cb43"
      }
    }
  ],
  "nodes": [
    { "name": "root", "children": [1] },
    { "name": "instanced", "children": [2, 3] },
    {
      "name": "705e25a1-127e-4d76-b5f5-4e766ef073a3-000f1bef",
      "mesh": 0,
      "extensions": {
        "EXT_mesh_gpu_instancing": {
          "attributes": {
            "TRANSLATION": 6,
            "ROTATION": 7,
            "SCALE": 8,
            "_FEATURE_ID_0": 9
          }
        },
        "EXT_instance_features": {
          "featureIds": [{ "featureCount": 4, "attribute": 0 }]
        }
      }
    },
    {
      "name": "705e25a1-127e-4d76-b5f5-4e766ef073a3-000f1d9e",
      "mesh": 1,
      "extensions": {
        "EXT_mesh_gpu_instancing": {
          "attributes": {
            "TRANSLATION": 10,
            "ROTATION": 11,
            "SCALE": 12,
            "_FEATURE_ID_0": 13
          }
        },
        "EXT_instance_features": {
          "featureIds": [{ "featureCount": 4, "attribute": 0 }]
        }
      }
    }
  ],
  "meshes": [
    {
      "name": "SM_Dining Chair (3)",
      "primitives": [
        {
          "attributes": { "POSITION": 3, "NORMAL": 4 },
          "indices": 2,
          "material": 0,
          "mode": 4,
          "extensions": {
            "KHR_draco_mesh_compression": {
              "bufferView": 2,
              "attributes": { "POSITION": 0, "NORMAL": 1 }
            }
          }
        }
      ]
    },
    {
      "name": "SM_Dining Chair (3)",
      "primitives": [
        {
          "attributes": { "POSITION": 6, "NORMAL": 7 },
          "indices": 5,
          "material": 0,
          "mode": 4,
          "extensions": {
            "KHR_draco_mesh_compression": {
              "bufferView": 3,
              "attributes": { "POSITION": 0, "NORMAL": 1 }
            }
          }
        }
      ]
    }
  ],
  "accessors": [
    {
      "bufferView": 0,
      "byteOffset": 0,
      "componentType": 5126,
      "count": 4,
      "type": "VEC3"
    },
    {
      "bufferView": 1,
      "byteOffset": 0,
      "componentType": 5126,
      "count": 4,
      "type": "SCALAR"
    },
    { "componentType": 5123, "count": 23328, "type": "SCALAR" },
    {
      "componentType": 5126,
      "count": 4766,
      "type": "VEC3",
      "max": [0.40068262341435573, 0.7755149427168185, 0.4090840279070497],
      "min": [
        -0.006055485716818494, -0.000621189416818494, -0.030884744616818494
      ]
    },
    {
      "componentType": 5126,
      "count": 4766,
      "type": "VEC3",
      "max": [1.007843137254902, 1.007843137254902, 1.008039537254902],
      "min": [-1.007843137254902, -1.007843137254902, -1.007646737254902]
    },
    { "componentType": 5123, "count": 23328, "type": "SCALAR" },
    {
      "componentType": 5126,
      "count": 4766,
      "type": "VEC3",
      "max": [0.40068262341435573, 0.7755149427168185, 0.4090840279070497],
      "min": [
        -0.006055485716818494, -0.000621189416818494, -0.030884744616818494
      ]
    },
    {
      "componentType": 5126,
      "count": 4766,
      "type": "VEC3",
      "max": [1.007843137254902, 1.007843137254902, 1.008039537254902],
      "min": [-1.007843137254902, -1.007843137254902, -1.007646737254902]
    }
  ],
  "bufferViews": [
    { "byteOffset": 0, "buffer": 0, "byteLength": 48, "byteStride": 12 },
    { "byteOffset": 48, "buffer": 0, "byteLength": 16, "byteStride": 4 },
    { "buffer": 0, "byteOffset": 64, "byteLength": 77274 },
    { "buffer": 0, "byteOffset": 77344, "byteLength": 77274 }
  ],
  "materials": [
    {
      "name": "M_Phase - Exist",
      "pbrMetallicRoughness": {
        "baseColorFactor": [0.498039216, 0.498039216, 0.498039216, 1],
        "metallicFactor": 0,
        "roughnessFactor": 0.609375
      },
      "doubleSided": true,
      "emissiveFactor": [0, 0, 0],
      "alphaMode": "OPAQUE"
    }
  ],
  "buffers": [
    { "name": "rac_basic_sample_project_test_draco", "byteLength": 154624 }
  ],
  "extensionsUsed": [
    "EXT_mesh_gpu_instancing",
    "EXT_instance_features",
    "KHR_draco_mesh_compression"
  ],
  "extensionsRequired": [
    "EXT_mesh_gpu_instancing",
    "KHR_draco_mesh_compression"
  ]
}

[lanvada]

glb model:
rac_basic_sample_project_test.zip

[lanvada]

I have fixed this issue myself.