UnityGLTF

Unity3D library for importing and exporting glTF 2.0 assets.

	Editor	Runtime
Import	✅	✅
Export	✅	✅

UnityGLTF doesn't have any native dependencies (pure C#) and thus works on all platforms that Unity supports. This includes WebGL import and export.

The library is designed to be easy to extend with additional extensions to the glTF specification. Both import and export allow attaching custom plugins and callbacks and can be heavily modified to fit into specific pipelines. Many glTF extensions are supported.

Contents

• Installation
• Unity Version and Render Pipeline Compatibility
• UnityGLTF and glTFast
• Supported Features and Extensions
  • Import and Export
  • Import only
  • Export only
• glTF Interactivity
  • Visual Scripting Graph Exporter
  • Features
  • Unsupported
  • Viewer support
• glTF Materials
  • Material Conversions
  • Material and Shader Export Compatibility
  • Configure for Refractive Materials (Transmission and Volume)
    • Material Setup
    • URP
    • Built-In
    • HDRP
• Exporting glTF Files
  • Testing, debugging, compatibility
• Animation Export
  • Animator Controller
  • GLTFRecorder API
  • Timeline Recorder
  • Legacy Animation Component
  • KHR_animation_pointer support
• Blend Shape Export
• Importing glTF files
  • Runtime Import
    • Load via Gltf Component
    • Load via code example:
  • Ensure shaders are available in your build
  • Editor Import
  • Default Importer Selection
• Animation Import
• Extensibility
  • Example for custom export plugin
  • Example for custom import plugin
• Known Issues
• Contributing
  • Unity Package
  • GLTFSerializer
  • Tests

Installation

You can install this package from the Needle Package Registry with a one-click installer:

1. Download UnityGLTF Package Installer
2. Drop the downloaded .unitypackage into Unity and follow the steps.

You can also install this package from git, compatible with UPM (Unity Package Manager).

1. Open Window > Package Manager
2. Click +
3. Select Add Package from git URL
4. Paste

   https://github.com/KhronosGroup/UnityGLTF.git
   

5. Click Add.

Note: If you want to target a specific version, append #release/<some-tag> or a specific commit to the URL above. Example: https://github.com/KhronosGroup/UnityGLTF.git#release/2.14.1.

Unity Version and Render Pipeline Compatibility

Please use Long-Term Support versions of Unity (2021.3+, 2022.3+, 6000.0+).

Recommended:

• Unity 2021.3+, Unity 2022.3+, Unity 6+
• Linear colorspace
• Universal Render Pipeline (URP) and Built-In Render Pipeline (BiRP)

HDRP:

• Currently limited functionality.

Legacy:

• When using Unity 2020.3, please use an older version of UnityGLTF, like 2.9.1-rc and before.

Note: Issues on non-LTS Unity versions (not on 2021.3, 2022.3, 6000.0...) will most likely not be addressed. Please use LTS (Long-Term Support) versions where possible.

UnityGLTF and glTFast

A separate glTF implementation for Unity, glTFast, is available from the Unity Registry.
glTFast being supported by Unity means, in a nutshell, that it sticks to standards pretty strictly and can't easily ship non-ratified extensions or experimental features that work for the majority, but not all, of users.

• UnityGLTF aims to be the more flexible framework, with extensive import/export plugin support and useful plugins out of the box.
• glTFast aims to be the more performant framework, with a focus on leveraging Unity-specific features such as Burst and Jobs.
• UnityGLTF has a versatile plugin/extension infrastructure. This allows for a lot of flexibility during import/export.
• UnityGLTF enables the use of and ships with non-ratified extensions such as KHR_animation_pointer, KHR_audio, and KHR_materials_variants.
• glTFast leverages Unity-specific features such as Burst and Jobs and thus can have better performance in some cases.
• glTFast has better HDRP support.

glTFast and UnityGLTF can coexist in the same project; you can for example use glTFast for import and UnityGLTF for export.
For imported assets, you can choose which importer to use with a dropdown.
glTFast import has precedence if both are in the same project. See also Default Importer Selection.

Supported Features and Extensions

The lists below are non-conclusive and in no particular order. Note that there are gaps where features could easily be supported for im- and export but currently aren't. PRs welcome!

Import and Export

• Animation and Animator with multiple clips
• Skinned Mesh Renderers
• Blend Shapes
  • Sparse accessors for Blend Shapes
• Linear and Gamma colorspace support (Gamma won't be maintained anymore)
• Vertex Colors
• Cameras (perspective, orthographic)
• URP and Built-In Render Pipeline Learn More
• KHR_lights_punctual (point, spot, and directional lights)
• KHR_texture_transform (UV offset, scale, rotation)
• KHR_materials_unlit (unlit surfaces)
• KHR_materials_transmission (glass-like materials)
• KHR_materials_volume (refractive materials)
• KHR_materials_ior (for transmission and volume)
• KHR_materials_emissive_strength (emissive values greater than 1)
• KHR_materials_iridescence (thin-film interference, like oil on water)
• KHR_materials_clearcoat (secondary specular layer, like a coat of varnish)

Import only

• KHR_mesh_quantization (smaller buffers / smaller filesize)
• KHR_draco_mesh_compression (requires com.unity.cloud.draco)
• KHR_texture_basisu (requires com.unity.cloud.ktx)
• EXT_mesh_gpu_instancing (instance data)
• EXT_meshopt_compression (requires com.unity.meshopt.decompress)

Export only

• KHR_materials_variants
• KHR_interactivity (Visual Scripting Graph exporter)
• Timeline recorder track for exporting animations in the editor and at runtime
• Lossless keyframe optimization on export
• All 2D textures can be exported, RenderTextures included – they're baked at export.
• Optional plugin: Bake TMPro 3D objects to meshes on export
• Optional plugin: Bake Particle Systems to meshes on export
• Optional plugin: Bake Canvas to meshes on export
• Included plugin sample: KHR_audio_emitter

glTF Interactivity

Visual Scripting Graph Exporter

This plugin allows you to export VisualScripting Graphs as KHR_interactivity graphs in glTF files.

Features

A wide range of nodes are supported for export. Additionally, many features that Unity's Visual Scripting has, but that are lacking in the KHR_interactivity extension, are "flattened" on export into compatible graph logic. For example, scoped variables get exported as variables with unique names, so that there are no conflicts in the exported graph. This allows a lot of flexibility for building complex graphs in the Unity editor, while still being able to export to a glTF file.

• SubGraph support
  • SubGraphs will be flattened on export
• Variables
  • "Saved" variables are not supported
• Custom Events
• Coroutines
• Multiple Visual Scripting Graphs in one glTF file
  • Multiple graphs will be merged into a single KHR_interactivity graph
• Partial List/Array support
  • Capacity of lists can't be changed at runtime, so make sure you create a List with enough size in the Visual Scripting graph.
• Math, Vector, Matrix operations
• Partial Animator support
  • Starting an animation is supported. Automatic graph transitions are currently not supported.
• Logic operations
• Material editing: Get/Set of floats, colors, texture offset/scale
• Property interpolation: Use the "Interpolate ..." family of nodes

A lot of Visual Scripting nodes are already supported. To see the full list of supported nodes, click on the button Project Settings > UnityGLTF > Export > KHR_interactivity (VisualScripting) > Log supported Visual Scripting Units to see the full list of supported nodes in the console.

[!TIP]
When the interactivity extension is enabled, you can also see in the Visual Scripting Editor which nodes are supported by the extension. You can also see any warnings/errors from the last exporting there (sometimes the editor will not be immediately updates the view and need some time).
Example: On Pointer Click is supported, while On Pointer Up is not supported for export.

Unsupported

• String manipulation (not supported by the KHR_interactivity extension)
• Some nodes have additional limitations. You can see these in the Script Graph:
  

Viewer support

These viewers support the current KHR_interactivity specification and have been extensively tested with the UnityGLTF exporter:

• Babylon: https://sandbox.babylonjs.com/
• Khronos Interactivity Graph Authoring Tool https://github.khronos.org/glTF-InteractivityGraph-AuthoringTool/

glTF Materials

The glTF shading model is physically based and supports many different types of surfaces. To use this extended material model of glTF in Unity, use the UnityGLTF/PBRGraph material.
It allows the use of various glTF material extensions for import, export, and inside Unity. The shader includes a number of features that URP is missing, such as transmission and rough refraction, sheen and clearcoat, and per-texture UV control. For unlit materials, use UnityGLTF/UnlitGraph.

Material Conversions

UnityGLTF contains helpers to make converting to UnityGLTF/PBRGraph easy.
When you switch a material from any shader to PBRGraph, an automatic conversion can run to bring the properties over.
Some shaders already come with automatic conversions, please see the table below.

When a shader doesn't have a converter yet, UnityGLTF will ask if you want to create a Conversion Script. These scripts contain all properties of the source shader and the target shader, but no specified mapping yet (as that depends on the intent of the shader author).
After the conversion script has been created, you can edit it to correctly map from the source shader's properties to PBRGraph properties.
When you switch such a shader to PBRGraph the next time, your conversion script will run and automatically translate the materials in the specified way.

Note: Currently, custom conversion scripts aren't used automatically on glTF export. For best results, convert materials in the Editor.

Material and Shader Export Compatibility

If you want to design for glTF export, it's recommended to use Unity 2021.3+ with URP and the UnityGLTF/PBRGraph material. It comes with support for modern material extensions like refraction and iridescence, and allows for perfect roundtrips. This material works great for building glTF pipelines in and out of Unity.

Render Pipeline	Used Shader	Notes	Source
URP on 2020.3+Built-In on 2021.3+	UnityGLTF/PBRGraph ☝️ Use this if you're not sure	Perfect roundtrip, Material Extensions	UnityGLTF
	UnityGLTF/UnlitGraph	Perfect roundtrip	UnityGLTF
	ShaderGraphs/glTF-pbrMetallicRoughness		glTFast
	ShaderGraphs/glTF-unlit		glTFast
URP	URP/Lit		Unity
	URP/Unlit		Unity
Built-In	Standard		Unity
	GLTF/PbrMetallicRoughness		UnityGLTF (legacy)
	GLTF/Unlit		UnityGLTF (legacy)
	glTF/PbrMetallicRoughness		glTFast (legacy)
	glTF/Unlit		glTFast (legacy)
HDRP (limited support)	HDRP/Lit		Unity
	HDRP/Unlit		Unity

Configure for Refractive Materials (Transmission and Volume)

Transmission and Volume allow rendering materials like glass, that are fully transparent but still show reflections, as well as volume attenuation (e.g. colored jelly) and rough refraction (e.g. brushed glass). To use these material features, you need to do some setup on the material and your render pipeline.

Material Setup

1. On a PBRGraph material, check "Enable Transmission" and optionally "Enable Volume"
2. Change the Transmission, Thickness, Index of Refraction and Attenuation values as desired.

URP

To see transmissive and volume materials correctly in Unity,

1. Select your URP Renderer Asset
2. Under the "Renderer Features" section, add a "Opaque Texture (Rough Refraction)" feature

Built-In

To see transmissive and volume materials correctly in Unity,

1. Add the "RoughRefraction" component to your Main Camera.

HDRP

HDRP has its own rough refraction support. There's currently no automatic import / export support to convert to that. Use glTFast if you need this.

Note: Fully metallic materials are never transparent. See the KHR_materials_transmission spec for more info.

Exporting glTF Files

To export an object from a scene or your project,

1. Select the object
2. Use the menu items under Assets > UnityGLTF > Export selected as GLB / Export selected as glTF to export

Tip: You can set shortcuts for quick export in Unity's Shortcut Manager. For example, Ctrl + Space for GLB export and Ctrl + Shift + Space for glTF export allow for very fast iteration.

Testing, debugging, compatibility

The various glTF viewers in existence have varying feature sets. Only a select few have full coverage of the glTF spec, most only support a subset.
Notable features with limited support:

• setting textureCoord per texture.
• setting textureRotation. Many viewers simply ignore it.
• sparse accessors. Some viewers support sparse accessors only for blend shapes, others don't support it at all.
• vertex colors.

To view your glTF files, here's a number of tools you can use:

Name	Notes
Khronos glTF Sample Viewer	Full support for ratified extensions
gltf.report	Inspect file size, meshes, textures
model-viewer	Support for KHR_materials_variants with custom code
Gestaltor	Full glTF Spec ComplianceSupport for KHR_animation_pointerSupport for KHR_audioSupport for KHR_materials_variants
Needle Viewer	Support for KHR_animation_pointerInspect hierarchy, textures, cameras, lights, warnings
Babylon.js Sandbox	Support for KHR_animation_pointer
UnityGLTF(this project!)	Simply drop the exported glb file back into Unity.
glTFast	Add the glTFast package to your project.You can switch the used importer on glTF files between glTFast and UnityGLTF.

To further process files after exporting them with UnityGLTF, you can use:

Name	Notes
gltf-transform	Compress meshes with draco or meshoptCompress textures to ktx2Optimize FilesConvert between .gltf and .glb
Blender	Import/export glTF files with good feature coverage

Animation Export

Animations can be exported both in the Editor and at runtime. Editor export works with Animator (multiple clips), Animation (multiple clips), and Timeline (GLTFRecorderTrack).

Animator Controller

You can export entire Animators and their clips as glTF files with multiple animations.
Animation clips will be named after each Motion State in the Animator Controller.
The "speed" property of each Motion will be baked into the exported clip. Ensure the speed is 1 when you want to export unchanged.
Any number of Animators in a hierarchy is supported, as is any number of clips in those.

Both Humanoid and Generic animations will be exported. Humanoid animations are baked onto the target rig at export time.

Note: Animator export only works in the Editor. For runtime export, use the GLTFRecorder capabilities or the Timeline Recorder.

GLTFRecorder API

For creating and/or recording animations at runtime, you can use the GLTFRecorder API. It allows to capture the state of entire hierarchies and complex animations and export them directly as glTF file, optionally with KHR_animation_pointer support for complex material and property animations.
See GLTFRecorderComponent for an example implementation.

Timeline Recorder

Timelines or sections of them can be recorded with a GltfRecorderTrack and one or more GltfRecorderClips. Timeline recording uses the GLTFRecorder API under the hood.

Legacy Animation Component

Note: Animation Component export only works in the Editor since Unity does not provide the required runtime access. For runtime export, use the GLTFRecorder capabilities.

Animation components and their legacy clips can also be exported.

KHR_animation_pointer support

UnityGLTF supports importing and exporting animations with the KHR_animation_pointer extension. The core glTF spec only allows animation node transforms and blend shape weights, while this extension allows animating arbitrary properties in the glTF file – including material and object properties, even in custom extensions and script components.

Exporting with KHR_animation_pointer can be turned on in Project Settings > UnityGLTF by enabling the KHR_animation_pointer plugin.

Note: The exported files can be viewed with Gestaltor, Babylon Sandbox, and Needle Engine, but currently not with three.js / model-viewer. See https://github.com/mrdoob/three.js/pull/24108.

Blend Shape Export

Morph Targets / Blend Shapes / Shape Keys are supported, including animations.
To create smaller files for complex blend shape animations (e.g. faces with dozens of shapes), export with the "Sparse Accessors" setting enabled.

Importing glTF files

Runtime Import

Load via Gltf Component

To import .gltf or .glb files at runtime, you can use the GLTFComponent for loading.

Load via code example:

From local file:

string dir = "C:\SamplePath\";
string filename = "AntiqueCamera.glb";

var importOpt = new ImportOptions();
importOpt.DataLoader = new UnityWebRequestLoader(dir);
var import = new GLTFSceneImporter(filename, importOpt);
await import.LoadSceneAsync();

From Web:

string uriDir = "https://github.com/KhronosGroup/glTF-Sample-Models/raw/refs/heads/main/2.0/AntiqueCamera/glTF-Binary/";
string filename = "AntiqueCamera.glb";

var importOpt = new ImportOptions();
importOpt.DataLoader = new UnityWebRequestLoader(uriDir);
var import = new GLTFSceneImporter(filename, importOpt);
await import.LoadSceneAsync();

Accessing the loaded gltf scene:

import.LastLoadedScene

On the loaded gltf scene you will find the InstantiatedGLTFObject component. Use the method Duplicate from it, to create a copy of the loaded scene.

Ensure shaders are available in your build

Please make sure you have added the UnityGLTFShaderVariantCollection (or UnityGLTFShaderVariantCollection-BiRP for BuildIn render pipeline) in the Project Settings > Graphics > Preloaded Shaders. Otherwise, it's possible that shaders are missing in build. Please be aware, that on the first build the compile time can take some time.

When you building for mobile platforms and you have the requirement for smaller shader sizes, and you know which shaders features you realy need, it might be better to create your own Shader Variant Collection.

You can also strip additional shader variants under Project Settings > UnityGtlf > Build to reduce shader compile time.

Editor Import

For importing .gltf or .glb files in the editor, place them in your project as usual (Assets or Packages). Make sure to bring .bin/textures along for .gltf files with the correct relative paths;.glb is usually self-contained.

When moving .gltf files inside Unity, make sure to move their .bin/texture files as well, to not break the path references between them.

Default Importer Selection

UnityGLTF will register itself as the default importer for the .gltf and .glb extensions.
If the glTFast package is also present in a project, glTFast gets precedence and UnityGLTF is available as Importer Override, which can be selected from a dropdown on each glTF asset.

UnityGLTF uses Unity's ScriptedImporter system. For any given file format (file extension) there has to be one default importer and there can be additional, alternative importers.
You can make UnityGLTF the default importer and de-prioritize glTFast by adding the following settings to your project's Scripting Defines:

GLTFAST_FORCE_DEFAULT_IMPORTER_OFF
UNITYGLTF_FORCE_DEFAULT_IMPORTER_ON

Care has been taken to align glTFast's and UnityGLTF's importers, so that in most cases you can switch between them without breaking prefab references. That being said, switching between importers can change material references, mesh references etc., so some manual adjustments may be needed. You may have to adjust the root stripping settings of each importer (glTFast and UnityGLTF do that slightly differently).

Animation Import

Animations can be imported both in the Editor and at runtime.
On the importer, you can choose between "Legacy", "Mecanim" or "Humanoid" clips.

At runtime, if you're importing "Mecanim" clips, you need to make sure to add them to a playable graph via script (e.g. Animator Controller or Timeline) to play them back.

Extensibility

UnityGLTF has import and export plugins. These have callbacks for modifying node structures, extension data, materials and more as part of the regular export and import process. They are used both in the Editor and at runtime. You can make your own plugins and enable them in the Project Settings > UnityGLTF menu.
Plugins are ScriptableObjects that can have settings; they're serialized as part of the GLTFSettings asset. Plugins create concrete instances of import/export handlers.

To create a plugin, follow these steps:

1. Make a class that inherits from GLTFImportPlugin or GLTFExportPlugin. This is the ScriptableObject that contains plugin settings.
2. Also, make a class that inherits from GLTFImportPluginContext or GLTFExportPluginContext. This class has the actual callbacks.
3. Implement CreateInstance in your plugin to return a new instance of your plugin context.
4. Override the callbacks you want to use in your plugin context.

If your plugin reads/writes custom extension data, you need to also implement GLTF.Schema.IExtension for serialization and deserialization.

[!WARNING] ShouldNodeExport callback: Using this callback requires understanding of how glTF works. For example, if you filter out some bones of a skeleton on export, the result might not be valid glTF or might not display what you expect. Use with caution

Example for custom export plugin

public class MyExportPlugin : GLTFExportPlugin
{
    public override string DisplayName { get => "My Custom Plugin"; }
    public override bool EnabledByDefault => true;
    public override bool AlwaysEnabled => false;
    
    public override GLTFExportPluginContext CreateInstance(ExportContext context)
    {
        return new MyExportPluginContext();
    }
}

public class MyExportPluginContext: GLTFExportPluginContext
{
    public override bool ShouldNodeExport(GLTFSceneExporter exporter, GLTFRoot gltfRoot, Transform transform)
    {
        return !transform.CompareTag("ignore");
    }
}

Example for custom import plugin

public class MyImportPlugin: GLTFImportPlugin
{
    public override string DisplayName => "My Import Plugin";
    public override string Description => "";
    
    public override GLTFImportPluginContext CreateInstance(GLTFImportContext context)
    {
        return new MyImportPluginContext();
    }
}

public class MyImportPluginContext: GLTFImportPluginContext
{
    public override void OnAfterImportScene(GLTFScene scene, int sceneIndex, GameObject sceneObject)
    {
        // Set all to static
        var objs = sceneObject.GetComponentsInChildren<Transform>();
        foreach (var obj in objs)
            obj.gameObject.isStatic = true;
    }
}

🏗️ Under construction. You can take a look at MaterialVariantsPlugin.cs for an example.

Known Issues

• Blend shape in-betweens will not be exported as glTF does not have that functionality.
• Support for glTF files with multiple scenes is limited.

Contributing

UnityGLTF is an open-source project. Well-tested PRs are welcome.

UnityGLTF is currently maintained by

• prefrontal cortex, member of the Khronos Group and
• Needle, member of the Metaverse Standards Forum.

Note: As of 20240129, the default branch of this repository has been renamed from master to main.

🏗️ Under construction. Feel free to raise an issue if you have questions.

Unity Package

• Unity Version Be sure that the Unity release you have installed on your local machine is at least 2021.3.
• Project Components The Unity project offers two main functionalities: importing and exporting GLTF assets. These functionalities are primarily implemented in GLTFSceneImporter and GLTFSceneExporter.

GLTFSerializer

• Basic Rundown: The GLTFSerializer facilitates serialization of the Unity asset model, and deserialization of GLTF assets.

• Structure:

  • Each GLTF schemas (Buffer, Accessor, Camera, Image...) extends the basic class: GLTFChildOfRootProperty. Through this object model, each schema can have its own defined serialization/deserialization functionalities, which imitate the JSON file structure as per the GLTF specification.
  • Each schema can then be grouped under the GLTFRoot object, which represents the underlying GLTF Asset. Serializing the asset is then done by serializing the root object, which recursively serializes all individual schemas. Deserializing a GLTF asset is done similarly: instantiate a GLTFRoot, and parse the required schemas.

Tests

🏗️ Under construction. Tests are currently in a separate (private) repository due to test asset licensing reasons.

To run tests with UnityGLTF as package, you'll have to add UnityGLTF to the "testables" array in manifest.json:

"testables": [
	"org.khronos.unitygltf"
]