Add KHR_materials_retroreflection extension#2610
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bsdorra
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Jul 12, 2026
lexaknyazev
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Jul 12, 2026
- Changed wording to apply only to the metallic and dielectric BRDFs of the material model. - I decided to go with Bastian's "metallic and dielectric" wording after all, since the Fresnel term in each one is affected. - I also decided to go with code formatting instead of equations for the Retroreflection section, so we use exactly the same variable names and formatting as Appendix B. - A few small tweaks and additions here and there, but mostly uses Bastian's wording. - Removed sample asset references and section - Removed clamping on `retroreflectionTexture` - Changed the lobe discussion section to say why this doesn't apply to clearcoat and sheen lobes based on Monday's WG conversations - Added Bastian and Alexey as contributors
…ts-2026-07-17 Edits from last week's extension review
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Overview
This PR proposes a new Khronos extension,
KHR_materials_retroreflection, which adds a physically-plausible retroreflective response to any glTF material model.It is based on the Minimal Retroreflective Microfacet (MRM) model of Portsmouth et al., JCGT 15(1), 2026: a BSDF is made retroreflective by substituting the outgoing view direction
Vwith its reflection about the surface normal before evaluation and sampling, redirecting the specular peak into the back-scatter direction. This produces the bright highlight seen on high-visibility clothing, glass-bead road markings, and safety signs. The model preserves reciprocity and energy conservation under reflection-symmetric NDFs (GGX, Beckmann, Phong).A
retroreflectionFactorlinearly blends between the standard material (0.0) and the retroreflective material (1.0), matching OpenPBR'sspecular_retroreflectivityparameter. An optionalretroreflectionTextureprovides a per-texel multiplier.Contents
README.md)material.KHR_materials_retroreflection.schema.json)Status
Draft
Relationship to other work
Aligns with the retroreflection models in OpenPBR 1.1 and MaterialX.
Known implementations
Contributors