KHR_materials_ior

extensions/2.0/Khronos/KHR_materials_ior/README.md

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+# KHR\_materials\_ior
+
+## Contributors
+
+* Tobias Haeussler, Dassault Systemes [@proog128](https://github.com/proog128)
+* Bastian Sdorra, Dassault Systemes [@bsdorra](https://github.com/bsdorra)
+* Ben Houston, ThreeKit [@bhouston](https://github.com/bhouston)
+* Richard Sahlin, IKEA [@rsahlin](https://github.com/rsahlin)
+* Norbert Nopper, UX3D [@UX3DGpuSoftware](https://twitter.com/UX3DGpuSoftware)
+* Ed Mackey, AGI [@emackey](https://twitter.com/emackey)
+
+Copyright (C) 2018-2020 The Khronos Group Inc. All Rights Reserved. glTF is a trademark of The Khronos Group Inc.
+See [Appendix](#appendix-full-khronos-copyright-statement) for full Khronos Copyright Statement.
+
+## Status
+
+Experimental
+
+## Dependencies
+
+Written against the glTF 2.0 spec.
+
+## 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
+
+The dielectric BRDF of the metallic-roughness material in glTF uses a fixed value of 1.5 for the index of refraction. This is a good fit for many plastics and glass, but not for other materials like water or asphalt, sapphire or diamond. This extensions allows users to set the index of refraction to a certain value.
+
+## Extending Materials
+
+The index of refraction of a material is configured by adding the `KHR_materials_ior` extension to any glTF material. 
+
+```json
+{
+    "materials": [
+        {
+            "extensions": {
+                "KHR_materials_ior": {
+                    "ior": 1.4,
+                }
+            }
+        }
+    ]
+}
+```
+
+| |Type|Description|Required|
+|-|----|-----------|--------|
+| **ior** | `number` | The index of refraction. | No, default: `1.5`|
+
+Typical values for the index of refraction range from 1 to 2. In rare cases values greater than 2 are possible. The following table shows some materials and their index of refraction:
+
+| Material     | Index of Refraction |
+|--------------|---------------------|
+| Air          | 1.0                 |
+| Water        | 1.33                |
+| Eyes         | 1.38                |
+| Window Glass | 1.52                |
+| Sapphire     | 1.76                |
+| Diamond      | 2.42                |
+
+The ior parameter affects the `dielectric_brdf` of the glTF 2.0 metallic-roughness material. The new `dielectric_brdf` that includes the `ior` parameter is given as follows:
+
+```
+dielectric_brdf =
+  fresnel_mix(
+    ior = ior,
+    base = diffuse_brdf(
+      color = baseColor),
+    layer = specular_brdf(
+      α = roughness^2))
+```
+
+## Implementation
+
+*This section is non-normative*
+
+The extension changes the computation of the Fresnel term defined in [Appendix B](/specification/2.0/README.md#appendix-b-brdf-implementation) to the following:
+
+```
+const dielectricSpecular = ((ior - 1)/(ior + 1))^2
+```
+
+Note that for the default index of refraction `ior = 1.5` this term evaluates to `dielectricSpecular = 0.04`.
+
+## Interaction with other extensions
+
+If `KHR_materials_specular` is used in combination with `KHR_materials_ior`, the Fresnel term is additionally scaled by the values given `specular` and `specularColor`. See [`KHR_materials_specular`](../KHR_materials_specular/README.md) for more information.
+
+If `KHR_materials_transmission` is used in combination with `KHR_materials_ior`, the `ior` affects the strength of the transmission effect according to the Fresnel term. See [`KHR_materials_transmission`](../KHR_materials_transmission/README.md) for more information. If `KHR_materials_specular` is used in addition, the Fresnel term is additionally scaled by the values given in `specular` and `specularColor`.
+
+If `KHR_materials_volume` is used in combination with `KHR_materials_ior`, the `ior` affects the refraction effect. See [`KHR_materials_volume`](../KHR_materials_volume/README.md) for more information.
+
+## Schema
+
+- [glTF.KHR_materials_ior.schema.json](schema/glTF.KHR_materials_ior.schema.json)
+
+## Appendix: Full Khronos Copyright Statement
+
+Copyright 2018-2020 The Khronos Group Inc.
+
+Some parts of this Specification are purely informative and do not define requirements
+necessary for compliance and so are outside the Scope of this Specification. These
+parts of the Specification are marked as being non-normative, or identified as
+**Implementation Notes**.
+
+Where this Specification includes normative references to external documents, only the
+specifically identified sections and functionality of those external documents are in
+Scope. Requirements defined by external documents not created by Khronos may contain
+contributions from non-members of Khronos not covered by the Khronos Intellectual
+Property Rights Policy.
+
+This specification is protected by copyright laws and contains material proprietary
+to Khronos. Except as described by these terms, it or any components
+may not be reproduced, republished, distributed, transmitted, displayed, broadcast
+or otherwise exploited in any manner without the express prior written permission
+of Khronos.
+
+This specification has been created under the Khronos Intellectual Property Rights
+Policy, which is Attachment A of the Khronos Group Membership Agreement available at
+www.khronos.org/files/member_agreement.pdf. Khronos grants a conditional
+copyright license to use and reproduce the unmodified specification for any purpose,
+without fee or royalty, EXCEPT no licenses to any patent, trademark or other
+intellectual property rights are granted under these terms. Parties desiring to
+implement the specification and make use of Khronos trademarks in relation to that
+implementation, and receive reciprocal patent license protection under the Khronos
+IP Policy must become Adopters and confirm the implementation as conformant under
+the process defined by Khronos for this specification;
+see https://www.khronos.org/adopters.
+
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extensions/2.0/Khronos/KHR_materials_ior/schema/glTF.KHR_materials_ior.schema.json

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+{
+    "$schema": "http://json-schema.org/draft-04/schema",
+    "title": "KHR_materials_ior glTF extension",
+    "type": "object",
+    "description": "glTF extension that defines the index of refraction of a material.",
+    "allOf": [ { "$ref": "glTFProperty.schema.json" } ],
+    "properties": {
+        "ior": {
+            "type": "number",
+            "description": "The index of refraction.",
+            "default": 1.5,
+            "minimum": 1.0,
+            "gltf_detailedDescription": "The index of refraction (IOR) is a measured physical number usually in the range between 1 and 2 that determines how much the path of light is bent, or refracted, when entering a material. It also influences the ratio between reflected and transmitted light, calculated from the Fresnel equations."
+        },
+        "extensions": { },
+        "extras": { }
+    }
+}