OpenMaterial_reference_link

OpenMaterial_reference_link

This is a proposal for an extension to the Khronos Group glTF 2.0 specification. OpenMaterial_reference_link enables referencing of other files from glTF (including glTF itself). Thus, it enables modularity and therefore improves exchangeability of assets and materials.

In order to use this extension, it has to be listed in the extensionsUsed section of the corresponding asset:

"extensionsUsed" : [
    "OpenMaterial_reference_link"
]

Properties

Within the following enlistment of properties specified by the proposed extension, items labeled as required are mandatory and must be present. Properties without required label are optional and may be omitted:

• title [string] Human-readable title of the referenced asset. This property is intended to help humans get an idea what the referenced asset is.

• uri [string][required] Uniform Resource Identifier (URI) that identifies the external referenced asset. The URI must conform to the RFC 3986 specification.

Note: An implementation of this extension should at least support the file:// scheme and relative references. Relative paths are relative to the corresponding asset. In addition to the schemes defined by RFC 3986, implementation may support the scheme id:// to allow referencing other assets by the id property specified in OpenMaterial_asset_info.

Example: Referencing materials

The asset file cube.gltf contains geometry and references material from aluminium.gltf:

{
    "asset": {...},
    "scenes": [...],
    "nodes": [...],
    "meshes": [...],
    "materials": [
        {
            "extensions": {
                "OpenMaterial_reference_link": {
                    "title": "aluminium",
                    "uri": "aluminium.gltf"
                }
            }
        }
    ],
    "accessors" : [...],
    "bufferViews" : [...],
    "buffers" : [...],
    "extensionsUsed": [
        "OpenMaterial_reference_link"
    ]
}

The material file aluminium.gltf contains material properties:

{
    "asset": {...},
    "materials": [
        {
            "name": "aluminium",
            "extensions": {
                "OpenMaterial_material_parameters": {
                    "user_preferences": {
                        "geometrical_optics": true,
                        "include_diffraction": false,
                        "include_numerical_simulation": false,
                        "material_scheme": "surface",
                        "material_classification": "solid-metal",
                        "material_type": {
                            "isotropic": true,
                            "homogeneous": true,
                            "magnetic": false
                        },
                        "temperature": 300.0,
                        "surface_displacement_uri": "",
                        "surface_roughness": {
                            "surface_height": 0.0,
                            "surface_correlation_length": 0.0
                        },
                        "coating_materials": [],
                        "lambert_emission": 0.0,
                        "subsurface": {
                          "subsurface": false,
                          "subsurface_thickness": 0.0
                        },
                        "ingredients": []
                    },
                    "physical_properties": {
                        "refractive_index_uri": "data/aluminium_ior.gltf",
                        "mean_free_path": 0.0,
                        "particle_density": 0.0,
                        "particle_cross_section": 0.0,
                        "emissive_coefficient_uri": "",
                        "applicable_sensors": [
                            "camera",
                            "lidar",
                            "radar"
                        ]
                    }
                }
            }
        }
    ]
}

After resolving reference to material, cube.gltf would look like this:

{
    "asset": {...},
    "scenes": [...],
    "nodes": [...],
    "meshes": [...],
    "materials": [
        {
            "name": "aluminium",
            "extensions": {
                "OpenMaterial_material_parameters": {
                    "user_preferences": {
                        "geometrical_optics": true,
                        "include_diffraction": false,
                        "include_numerical_simulation": false,
                        "material_scheme": "surface",
                        "material_classification": "solid-metal",
                        "material_type": {
                            "isotropic": true,
                            "homogeneous": true,
                            "magnetic": false
                        },
                        "temperature": 300.0,
                        "surface_displacement_uri": "",
                        "surface_roughness": {
                            "surface_height": 0.0,
                            "surface_correlation_length": 0.0
                        },
                        "coating_materials": [],
                        "lambert_emission": 0.0,
                        "subsurface": {
                          "subsurface": false,
                          "subsurface_thickness": 0.0
                        },
                        "ingredients": []
                    },
                    "physical_properties": {
                        "refractive_index_uri": "data/aluminium_ior.gltf",
                        "mean_free_path": 0.0,
                        "particle_density": 0.0,
                        "particle_cross_section": 0.0,
                        "emissive_coefficient_uri": "",
                        "applicable_sensors": [
                            "camera",
                            "lidar",
                            "radar"
                        ]
                    }
                }
            }
        }
    ],
    "accessors" : [...],
    "bufferViews" : [...],
    "buffers" : [...],
    "extensionsUsed": [
        "OpenMaterial_material_parameters"
    ]
}

glTF Schema Updates

N/A

JSON Schema

OpenMaterial_reference_link.schema.json

Known Implementations

N/A