Wednesday, July 14th, 2021 Posted by Jim Thacker

glTF files can now include accurate translucent materials

The new IOR, specular and volume material extensions for glTF add realistic reflection and refraction to translucent materials on models in the real-time 3D file format. Image credits at the foot of the story.

Standards body Khronos Group has released three new PBR material extensions for the glTF asset format.

The new index of refraction, volume and specular extensions further improve the visual quality of the popular real-time 3D asset format – in particular, displaying translucent materials more accurately.

An evolving standard for 3D assets for use online, in games and augmented reality applications
First announced in 2013, glTF is a runtime-neutral specification for 3D content, primarily intended as a lightweight file format for assets that need to be rendered online or on mobile devices.

The format got a big boost in 2017, when version 2.0 of the spec introduced support for PBR materials, with a wide range of DCC applications and render engines subsequently adding glTF support.

Since then, Khronos Group has continued to extend glTF’s material capabilities, introducing the KTX 2.0 format for texture compression, and new extensions for Clear Coat, Transmission and Sheen properties.

Three new PBR material extensions for IOR, specularity and volume properties
Khronos Group has now added three further PBR material extensions:

KHR_materials_ior specifies a material’s index of refraction, and describes the way that light is scattered as it passes through translucent or transparent materials.

KHR_materials_specular describes a material’s specular properties. Unlike its predecessor, KHR_materials_pbrSpecularGlossiness, it works within a standard modern metallic/roughness PBR workflow.

KHR_materials_volume is probably the least self-descriptive of the three, and enables mesh surfaces to act as an interface between volumes to enable more realistic refraction and absorption.

For real-time engines incapable of ray tracing, the KHR_materials_volume extension also supplies a thickness texture map to enable “fast approximations of light interacting with a volume of material”.

Collectively, the new extensions enable assets stored in glTF format to recreate translucent materials more accurately, with more realistic reflections, refractions and colour attenuation.

Designed for ecommerce, but benefiting any 3D model
As with Khronos Group’s new certification scheme for online 3D model viewers, a key objective of the new extensions is to improve the fidelity of 3D assets displayed on ecommerce sites.

Technical contributors to the extensions include staff from online retailers Amazon, IKEA, Target and Wayfair.

“Online shoppers increasingly expect realistic, beautiful product imagery to be part of their online experience,” said Wayfair’s Shrenik Sadalgi, chair of the Khronos 3D Commerce working group.

“This latest set of PBR features is a game-changer for retailers, especially those in style-oriented categories like ‘Home’, who need their product models to stand out with the most visually realistic materials.”

However, with the glTF format now widely supported in DCC tools and online portfolio sites like Sketchfab, the benefits should carry over to artists working in media and entertainment.

Khronos Group is now working on further extensions for material properties like iridescence and anisotropy.

Support in 3D asset viewers and rendering engines
The three new PBR material extensions are fully supported in Khronos Group’s own glTF Sample Viewer, open-source web rendering engine BabylonJS and Gestaltor, UX3D’s commercial glTF editor.

Other tools should follow suit: Khronos’s news release namechecks new Adobe app Substance 3D Stager and Filament, Google’s physically based renderer for Android, as supporting “some or all” of the extensions.

Read more about the new PBR material extensions to glTF on Khronos Group’s website