ADOBE_materials_clearcoat_tint

Contributors

Status

Complete

Dependencies

Written against the glTF 2.0 spec.

  • Requires the KHR_materials_clearcoat extension to also be defined on the material

Exclusions

  • This extension must not be used on a material that also uses KHR_materials_pbrSpecularGlossiness.
  • This extension must not be used on a material that also uses KHR_materials_unlit.

Overview

This extension defines a way to tint the clear coating provided by the KHR_materials_clearcoat extension.

Extending Materials

Adding tint to clearcoat materials can be done by adding the ADOBE_materials_clearcoat_tint extension to any glTF material that already has the KHR_materials_clearcoat extension defined on it. For example, the following defines a material with a dark red varnish.

{
    "materials": [
        {
            "name": "varnish",
            "extensions": {
                "KHR_materials_clearcoat": {
                    "clearcoatFactor": 1.0
                },
                "ADOBE_materials_clearcoat_tint": {
                    "clearcoatTintFactor": [
                      0.4,
                      0.1,
                      0.1
                    ]
                }
            }
        }
    ]
}

Clearcoat Tint

All implementations should use the same calculations for the BRDF inputs. Implementations of the BRDF itself can vary based on device performance and resource constraints. See Appendix B for more details on the BRDF calculations.

As with the core glTF 2.0 spec, all coloured textures are assumed to be sRGB and all coloured factors are assumed to be linear.

  Type Description Required
clearcoatTintFactor number[3] The clearcoat tint’s colour factor. No, default: [1.0, 1.0, 1.0]
clearcoatTintTexture textureInfo The clearcoat layer’s tint texture. No

The clearcoat tint defines the transmittance of light through the coat. That is, it defines what colour of light is allowed to pass through. As with other factor/texture combinations, these two values are multiplied.

clearcoat_tint.rgb = clearcoatTintFactor.rgb * clearcoatTintTexture.rgb

The clearcoat_tint modifies the formula for f_clearcoat (as defined in KHR_materials_clearcoat) only slightly. The (f_emissive + f_diffuse + f_specular) term is simply multiplied by the clearcoat tint to represent the absorption of all light coming from the layer below.

clearcoatBlendFactor = clearcoatTexture.r * clearcoatFactor
clearcoatFresnel = fresnel(0.04, NdotV)

color = mix(vec3(1.0), clearcoat_tint, clearcoatBlendFactor) * (f_emissive + f_diffuse + f_specular) * (1.0 - clearcoatBlendFactor * clearcoatFresnel) +
        f_clearcoat * clearcoatBlendFactor

Schema