Bring extension into line with KHR_materials_ior and KHR_materials_specular

Author: MiiBond

extensions/2.0/Vendor/ADOBE_materials_clearcoat_ior/README.md

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+# ADOBE\_materials\_clearcoat\_ior
+
+## Contributors
+
+* Mike Bond, Adobe, [@miibond](https://twitter.com/miibond)
+
+## Status
+
+Draft.
+
+## 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 control the index of refraction (IOR) and specular F0 for the clearcoat layer that's provided by the `KHR_materials_clearcoat` extension. This overrides the default IOR for clearcoat (which is `1.5`) and also provides a way to modulate the F0 reflectivity. This is exactly analogous to the way that the `KHR_materials_ior` and `KHR_materials_specular` extensions work together to modify F0 reflectivity.
+
+## Extending Materials
+
+Adding reflectivity information to the clearcoat can be done by adding the `ADOBE_materials_clearcoat_specular` 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 clearcoat that has an IOR of 3.0.
+
+```json
+{
+    "materials": [
+        {
+            "name": "varnish",
+            "extensions": {
+                "KHR_materials_clearcoat": {
+                    "clearcoatFactor": 1.0
+                },
+                "ADOBE_materials_clearcoat_specular": {
+                    "clearcoatIor": 3.0
+                }
+            }
+        }
+    ]
+}
+```
+
+### Clearcoat Reflectivity
+
+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](/specification/2.0/README.md#appendix-b-brdf-implementation) 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             |
+|----------------------------------|---------------------------------------------------------------------------------|----------------------------------------|----------------------|
+|**clearcoatIor**               | `number`                                                                        | The clearcoat IOR.         | No, default: `1.5`   |
+|**clearcoatSpecularFactor**               | `number`                                                                        | The clearcoat specular factor.         | No, default: `1.0`   |
+|**clearcoatSpecularTexture**              | [`textureInfo`](/specification/2.0/README.md#reference-textureInfo)             | The clearcoat layer's specular amount, stored in the `B` channel of a texture. | No                   |
+
+The clearcoat Fresnel contribution is usually calculated just as described for the base layer in [Appendix B](/specification/2.0/README.md#appendix-b-brdf-implementation).
+This extension modifies the Fresnel contribution of clearcoat as follows:
+The `clearcoatIor` can be used to calculate the reflectance at normal incidence for the coating (`coatBaseF0`) that will replace the default `F0` of `0.04`.
+
+```
+coatBaseF0 = ((clearcoatIor - outside_ior) / (clearcoatIor + outside_ior))^2
+```
+
+Then, this can be used with the specular factor to determine the overall Fresnel contribution for the clear coating.
+
+```
+coatSpecularF0 = coatBaseF0 * clearcoatSpecularFactor * clearcoatSpecularTexture.b;
+coatSpecularF90 = clearcoatSpecularFactor * clearcoatSpecularTexture.b;
+
+clearcoatFresnel = coatSpecularF0 + (coatSpecularF90 - coatSpecularF0) * (1 - VdotH)^5;
+```
+
+Note that the specular factor texture data is read from the `B` channel so that the same RGB texture can be shared between the `KHR_materials_clearcoat` and `ADOBE_materials_clearcoat_specular` extensions.
+
+## Schema
+
+- [glTF.ADOBE_materials_clearcoat_specular.schema.json](schema/glTF.ADOBE_materials_clearcoat_specular.schema.json)
+ 

extensions/2.0/Vendor/ADOBE_materials_clearcoat_ior/schema/glTF.ADOBE_materials_clearcoat_ior.schema.json

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+{
+    "$schema": "http://json-schema.org/draft-04/schema",
+    "title": "ADOBE_materials_clearcoat_ior glTF extension",
+    "type": "object",
+    "description": "glTF extension that defines the colour tint of the clearcoat.",
+    "allOf": [ { "$ref": "glTFProperty.schema.json" } ],
+    "properties": {
+        "clearcoatIor": {
+            "type": "number",
+            "description": "The clearcoat layer's index of refraction.",
+            "default": 1.5,
+            "minimum": 0.0,
+            "maximum": 1.0,
+            "gltf_detailedDescription": "The clearcoat layer's index of refraction."
+        },
+        "clearcoatSpecularFactor": {
+            "type": "number",
+            "description": "The clearcoat layer's specular intensity.",
+            "default": 1.0,
+            "minimum": 0.0,
+            "maximum": 1.0,
+            "gltf_detailedDescription": "The clearcoat layer's specular intensity."
+        },
+        "clearcoatSpecularTexture": {
+            "allOf": [ { "$ref": "textureInfo.schema.json" } ],
+            "description": "The clearcoat layer specular intensity texture.",
+            "gltf_detailedDescription": "The clearcoat layer's specular intensity texture. These values are sampled from the B channel."
+        },
+        "extensions": { },
+        "extras": { }
+    }
+}