KHR_materials_ior

extensions/2.0/Khronos/KHR_materials_ior/README.md

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+# KHR\_materials\_ior
+
+## Khronos 3D Formats Working Group
+
+* TODO
+
+## Acknowledgments
+
+* TODO
+
+## Status
+
+Experimental
+
+## Dependencies
+
+Written against the glTF 2.0 spec.
+
+## 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 reflectance at normal incidence (F0) of dielectric materials is computed from the IOR as follows:
+
+```
+f0 = ((ior - outside_ior) / (ior + outside_ior))^2
+```
+
+The `outside_ior` determines the index of refraction of the medium on the outside. If the renderer does not track the IOR when traversing nested dielectrics, it can assume `outside_ior = 1`.
+
+For `ior = 1.5` and `outside_ior = 1`, the result is `f0 = 0.04`. This is the fixed value used in the glTF 2.0 metallic-roughness material. The extension makes this value configurable.
+
+
+## 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:
+
+```
+dielectricSpecular = ((ior - 1)/(ior + 1))^2
+```
+
+## Interaction with other extensions
+
+If `KHR_materials_specular` is used in combination with `KHR_materials_ior`, f0 computed from IOR is multiplied by f0 computed from the specular parameters. 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 rules for multiplying f0 from `ior` and f0 from the specular parameters apply as defined in `KHR_materials_specular`.
+
+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_specular.schema.json](schema/glTF.KHR_materials_specular.schema.json)

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": { }
+    }
+}