glTF: Now and Next - Khronos Blog

glTF: Now and Next - Khronos Blog
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glTF: Now and Next

by gltf

glTF™ has evolved beyond its origins as a standalone 3D format. It is now adopted as an ISO international standard and has become central to a rapidly expanding ecosystem of software tools, standards and extensions.

Given the central role of glTF in enabling 3D experiences across diverse platforms, devices and the web, it is crucial that the glTF ecosystem continue to evolve to meet the needs of content creators, engine vendors and application developers, as well as adapt to new use cases such as 3D shopping, education and training, architectural visualization, and many others.

This year, the Khronos 3D Formats Working Group has reached several significant milestones along the roadmap for developing glTF into an interoperable spatial computing format, and has several extension development efforts underway. Many key extensions for spatial consistency, improved material rendering and consistent render fidelity have now reached the Review Draft stage, where they are ready for detailed review and initial testing. There are also several new extensions in the Initial Draft phase, where the Working Group is seeking directional input to ensure specification development aligns with the community’s needs. We are cranking and getting work done!

This blog will review recent ecosystem updates, explain current specs nearing release candidacy, and highlight opportunities for community input, inviting glTF stakeholders to share useful feedback to shape the future development of the glTF ecosystem.

glTF Leveraged by Other Standards

Today, glTF is widely used and referenced as the foundational 3D scene format for many third-party industry standards developed by organizations in collaboration with Khronos:

Market-specific use of glTF in standards defined by third-party standards organizations

Khronos welcomes working collaboratively with other standards organizations that wish to leverage and extend glTF to meet market-specific needs, while cooperatively avoiding duplication and fragmentation of effort.

Cross-platform Compatibility

While glTF is already the most portable asset format for bringing 3D content to diverse platforms and browsers, we continue to work hard to make glTF accessible and usable wherever it is needed.

iOS Viewer

Late last year, Khronos released an open-source iOS App for viewing glTF files on Apple devices in 3D or AR: “Khronos glTF Viewer.” App users can display pre-loaded glTF sample models, or download GLB models from the web and view them interactively in the app.

At launch, the iOS viewer supported all base glTF 2.0 features and select extensions including Draco compression and the clearcoat PBR Extension. Khronos released full application source code on GitHub under an Apache 2.0 license. Developers are invited to use the source code to develop their own derivative projects and drive the proliferation of glTF 3D and AR viewers.

USD Interoperability

Within the Metaverse Standards Forum, Khronos is working to directly align with the Alliance for OpenUSD (AOUSD) and the Academy Software Foundation (ASWF) to advance cooperation between the glTF and USD ecosystems. This collaborative effort will make it easier to distill assets authored in USD into glTF and to remix existing glTF assets using USD’s rich authoring capabilities.

glTF PBR Material Updates

The 3D Formats Working Group and its physically based rendering (PBR) Subgroup are committed to improving workflows for the production of photorealistic, highly reusable 3D objects. glTF’s PBR shader extensions offer an artist-friendly, intuitive means to accurately represent a wide range of materials. PBR is driven by the need to maintain visual consistency across viewers and rendering outputs, and the Subgroup continues to add new capabilities through new PBR extensions. The Subgroup has also made excellent progress toward easier mapping between glTF PBR and MaterialX.

New glTF PBR Extensions

In April 2024, Khronos ratified KHR_materials_dispersion, which enables angular separation of colors when light is transmitted through a relatively clear volume. When representing materials like diamonds or cut glass, this extension allows artists to achieve a prismatic effect.

The PBR Subgroup is currently developing two new PBR extensions, slated for release in 2025:

  • Diffuse transmission
    • Development stage: Review Draft
    • KHR_materials_diffuse_transmission is a new extension for the metallic-roughness material that adds a translucency effect, for use with thin materials like leaves or paper. This extension can also be used in combination with KHR_materials_volume to suffuse light through volumetric materials like candle wax.
  • Subsurface scattering
    • Development stage: Initial Draft
    • KHR_materials_subsurface will extract the subsurface scattering parameters of KHR_materials_volume to their own extension, giving artists independent control of scattering and absorption.

glTF PBR/MaterialX Interoperability

MaterialX is an open standard from the Academy Software Foundation for representing visually rich materials. A MaterialX node that encapsulates glTF PBR materials has been available since 2022. In 2025, the Working Group aims to update the MaterialX glTF node with all ratified glTF PBR extension functionality. Next year Khronos also plans to make MaterialX-like procedural textures available as inputs to glTF rendering to add customizability, reduce asset sizes and support easier interchange between the glTF, MaterialX and USD ecosystems.

Visual Consistency

Achieving visual consistency across diverse platforms and engines is a significant 3D content development challenge. In addition to the steady advancement in glTF PBR standardization, Khronos offers a suite of tools to validate and preview assets, enabling artists to build an asset once and have it displayed consistently anywhere.

Render Fidelity Site

In 2024, the Khronos 3D Formats and 3D Commerce Working Groups are expanding the Render Fidelity project. This website offers side-by-side comparisons of leading real-time web renderers, giving content developers and brands insight into how their assets will perform in each engine. Khronos has taken over stewardship of this project, originally created by Google’s <model-viewer> team, and will soon add more renderers and an improved inspection website.

PBR Neutral Tone Mapper

True-to-life color representation is crucial in e-commerce, or any context where 3D assets are displayed side-by-side with photographs. This spring, Khronos ratified the Khronos PBR Neutral Tone Mapper, an alternative to filmic tone mappers that results in precise, 1:1 color representation in the final render under grayscale lighting, and objective color representation under colored light such as sunlight. Using this tone mapper, content creators can verify the color values for a glTF model in the texture file, rather than having to wait for the final render to verify whether a product model precisely matches brand colors. Khronos PBR Neutral Tone Mapper has already achieved wide adoption and support from 3D tools and engines including <model-viewer>, Autodesk, Babylon.js, Blender, Dassault, Filament, London Dynamics, Phasmatic, Three.js, and ThreeKit.

What’s Next: Spatial Computing, Interactivity, and More

Khronos has made significant strides this year in the evolution of glTF for use in immersive spatial computing applications. A series of new extensions slated for release candidacy in 2024 and 2025 will standardize physics, interactivity and audio metadata for 3D assets, allowing content creators to reuse an asset across multiple interactive scenes. At the same time, the Working Group is defining standards to streamline the creation of complex scenes from multiple external references.

  • Physics
    • Development Stage: Multiple Specifications in the Review Draft Phase
    • Anticipated release candidacy in 2024
    • KHR_physics_rigid_bodies introduces several new concepts to allow glTF models to be used in a rigid body physics simulation. It includes “motion properties” to describe how objects behave and “joints” to physically connect models, while filters and physics materials describe their collision response.
    • KHR_implicit_shapes describes parametric shapes such as spheres or capsules. This extension is useful for collision detection, but defined separately from KHR_physics_rigid_bodies to enable future use cases outside of physics.
  • Interactivity
    • Development Stage: Multiple Specifications in the Review Draft Phase
    • Anticipated release candidacy in 2024
    • KHR_interactivity adds the ability to encode behavior and interactivity in 3D assets. This extension is intended for use by both asset exporters/converters and application developers seeking to import or load 3D assets, creating the basis for interoperable interactive glTF files. There are several additional extensions intended for use in conjunction with KHR_interactivity to control the behavior of node hierarchies in a 3D scene:
  • Audio
    • Development Stage: Initial Draft
    • Anticipated release candidacy in 2025
    • The KHR_audio_graph draft proposal defines a glTF audio graph structure including a detailed description of each node object, functionality and properties associated with each node, and how each node interacts with other nodes in the graph.
  • External References

Get Involved

The glTF ecosystem is evolving rapidly and dramatically. Interested developers and content creators can view the current glTF Extensions Roadmap, including the development status of each extension, available on the glTF page. We welcome community feedback and input on in-development extensions via the roadmap GitHub links.

Of course, the best way to shape the future of glTF is to get involved in the Khronos Group - all interested companies are very welcome! Learn more about membership and secure a voice and vote in the future of 3D at Khronos.org/members.