# glTF Files This section provides additional information on the use of glTF files.
#### Animations There is a working sample available showing the usage of glTF animations. For this, please refer to [Physically Based Rendering Solution](https://doc316en.candera.eu/books/sample-solutions/page/physically-based-rendering-solution "Physically Based Rendering Solution") Interpolation animation is available, however Morphing and the channel path "weights" are not available. Animation of:
- translation - rotation - scale is available.
Also, the following Interpolation strategies are available:
- linear - step - cubicspline

In glTF rotation angles are specified in quaternions, for usage in CGIStudio, the values are converted to Euler-angles.

For a more detailed description on animations please refer to [the Khronos website: animations](https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#animations). For a more detailed description on interpolation types please refer to [the Khronos website: animation sampler](https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#reference-animation-sampler).
--- #### SDK version The glTF importer uses the Microsoft glTF-SDK in version v1.9.1.0. It can be downloaded from [Github](https://github.com/microsoft/glTF-SDK).
--- #### Reference models A reference model that is being used is the boombox. The glTF file is available at the folder cgi\_studio\_content/3D/glTF/. Available reference models can be found at: [The Khronos website: glTF Sample Models](https://github.com/KhronosGroup/glTF-Sample-Models).
#### Supported glTF Extensions and Multi UV Scene Composer’s glTF import supports the following glTF 2.0 extensions as well as multiple UV sets (Multi UV).
KHR\_lights\_punctualImports point, spot, and directional lights defined in the glTF file as lights in Scene Composer.
KHR\_materials\_anisotropyReproduce materials with anisotropic highlights, such as brushed metal.
KHR\_materials\_clearcoatReproduces materials that have a clear-coat layer (clear paint).
KHR\_materials\_iorSpecifies the Index of Refraction (IOR) and improves refraction for materials such as glass.
KHR\_materials\_iridescenceRepresents iridescence effects where the color changes depending on the viewing and incident angles.
KHR\_materials\_specular Supports materials that independently control the intensity and color of specular reflection.
KHR\_materials\_unlitSupports “unlit” materials that are not affected by lighting calculations.
KHR\_texture\_transformInterprets UV transforms such as offset, scale, and rotation per texture.
KHR\_materials\_emissive\_strengthThis extension scales the emissive color or texture by a scalar *emissiveStrength* factor, allowing materials to represent much brighter emission, especially in HDR rendering environments.
KHR\_materials\_sheenThis extension adds a sheen layer on top of an existing PBR material to simulate soft, fabric-like highlights caused by fine microfibers such as cloth or velvet.
Even when UV sets other than `uv0` are specified in these extensions, Scene Composer imports multiple UV sets (Multi UV) and assigns them to the corresponding textures. ##### Limitations - In ES 2.0 environments, due to the limitations of ES 2.0, importing some sample glTF files that use these extensions may not produce the expected visual results. - Some extensions, such as **KHR\_materials\_anisotropy**, **KHR\_materials\_iridescence**, **KHR\_materials\_specular**, **KHR\_materials\_ior**, **KHR\_materials\_emissive\_strength** and **KHR\_materials\_sheen** cannot be used together with KHR\_materials\_unlit by design. - Meshes that use **KHR\_materials\_anisotropy** must have normal and tangent attributes, or the base material must have a normal map. If these conditions are not met, the anisotropy effect may not be rendered correctly. For details on the properties and parameters of each extension, refer to the [glTF 2.0 extension specifications](https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Khronos) provided by Khronos. --- #### Pyhsically Based Shading (PBS) On the imported 3d model the metal roughness material model is applied. If no IBL textures are defined a default material is applied. The shaders are provided for OpenGL ES 2.0 and 3.0. In SceneComposer the properties are called differently from the glTF standard:
- the standard property baseColor is called u\_Base Color Factor - the standard property metallic is determined by the X value in the u\_Metallic Roughness Values - the standard property roughness is determined by the Y value in the u\_Metallic Roughness Values
The following properties of the appearance and shader are automatically set by the Importer, but can also be configured manually: ##### Uniforms:
- "u\_MetallicRoughnessValues" holds the metallic factor in X, and roughness factor in Y. These values are multiplied with the metallic and roughness values from the metallic-roughness texture on a per pixel basis. If there is no such texture, the values from the uniform are used instead. - "u\_BaseColorFactor" (RGBA) is multiplied with the value from the albedo texture on a per pixel basis. If there is no such texture, the values from the uniform are used instead. - "u\_MipmapCount" The number of mipmaps (excluding level 0) from the specular/radiance texture. - (Optional) "u\_NormalScale" is a factor that is multiplied with the X and Y component of the normal. This uniform is only available if HAS\_NORMALMAP has been defined in the fragment and vertex shader. - (Optional) "u\_OcclusionStrength" is a factor for the linear interpolation between the color and the color times ambient occlusion. This uniform is only available if HAS\_OCCLUSIONMAP is defined in the fragment and vertex shader. - (Optional) "u\_EmissiveFactor" (RGB) is multiplied with the value from the emissive texture on a per pixel basis. This uniform is only available if HAS\_ HAS\_EMISSIVEMAP is defined in the fragment and vertex shader.
##### Textures:
- (Optional) The albedo texture (RGBA) must be set at texture unit 0, and HAS\_BASECOLORMAP must be defined in the fragment shader. - (Optional) The metallic-roughness texture (GB) must be set at texture unit 1, and HAS\_METALROUGHNESSMAP must be defined in the fragment shader. The metallic values must be stored in blue channel. The roughness values must be stored in the green channel of the texture. - (Optional) The tangent-space normal (RGB) texture must be set at texture unit 2, and HAS\_NORMALMAP must be defined in the fragment and vertex shader. - (Optional) The occlusion texture (R) must be set at texture unit 3, and HAS\_OCCLUSIONMAP must be defined in the fragment and vertex shader. The occlusion values are stored in the red channel of the texture. - (Optional) The emissive texture (RGB) must be set at texture unit 4, and HAS\_EMISSIVEMAP must be defined in the fragment and vertex shader. - (Optional) IBL textures. The following textures must be present for IBL to work correctly. - The diffuse/irradiance cubemap (RGB) must be set at texture unit 5, and USE\_IBL must be defined in the fragment shader. - The specular/radiance cubemap (RGB) must be set at texture unit 6, and USE\_IBL must be defined in the fragment shader. The specular pre-convolved environment must be built into the mipmaps. The number of mipmaps (excluding level 0) is set in the shader uniform "u\_MipmapCount" automatically by the importer, or must be configured manually if this cubemap is set manually. - The BRDF texture (RG) must be set at texture unit 7, and USE\_IBL must be defined in the fragment shader.
Details of the imported appearance are shown in the scene tree:
##### Mesh:
- Position is mandatory. - (Optional) If the mesh has normals, HAS\_NORMALS must be defined in the fragment and vertex shader. - (Optional) If the mesh has tangents, HAS\_TANGENTS must be defined in the fragment and vertex shader. - (Optional) If the mesh as a uv set, HAS\_UV must be defined in the vertex shader.
[![glTF_shader_variants.png](https://doc316en.candera.eu/uploads/images/gallery/2023-02/scaled-1680-/gltf-shader-variants.png)](https://doc316en.candera.eu/uploads/images/gallery/2023-02/gltf-shader-variants.png)
*different shader variants (Click to enlarge image)*
##### Uniform Setter:
- Model View Projection matrix is mandatory. - Model matrix is mandatory. - Normal model matrix is mandatory if HAS\_NORMALS and HAS\_TANGENTS are defined in the shader.
##### Optimization tips:
- Use one texture for occlusion, roughness, and metallic values, stored as an RGB texture. - Providing tangents in the mesh avoids calculating the tangent space matrix on a per pixel basis.
For a more detailed description on Pysically Based Rendering please refer to [the Khronos website: metallic roughness](https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#reference-pbrmetallicroughness).
--- #### Useful links Khronos References
- glTF Overview ([https://www.khronos.org/gltf/](https://www.khronos.org/gltf/)) - glTF 2.0 Specification ([https://github.com/KhronosGroup/glTF/tree/master/specification/2.0](https://github.com/KhronosGroup/glTF/tree/master/specification/2.0)) - glTF 2.0 Sample Models ([https://github.com/KhronosGroup/glTF-Sample-Models/tree/master/2.0](https://github.com/KhronosGroup/glTF-Sample-Models/tree/master/2.0))
Khronos Specification
- Specification ([https://github.com/KhronosGroup/glTF](https://github.com/KhronosGroup/glTF))
Viewers
- BabylonJS Sandbox ([https://sandbox.babylonjs.com/](https://sandbox.babylonjs.com/)) - donmccurdy glTF viewer ([https://gltf-viewer.donmccurdy.com/](https://gltf-viewer.donmccurdy.com/)) - Khronos glTF Sample Viewer ([https://github.khronos.org/glTF-Sample-Viewer-Release/](https://github.khronos.org/glTF-Sample-Viewer-Release/))