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,
+                    "iorTexture": 0
+                }
+            }
+        }
+    ]
+}
+```
+
+The index of refraction typically is a value between 1 and 2, in rare cases it may be larger than 2. In contrast to other texturable values in glTF, `ior` and `iorTexture` are not multiplied: if no texture is given, `ior` is used, otherwise the texture overrides it.
+
+| |Type|Description|Required|
+|-|----|-----------|--------|
+| **ior** | `number` | The index of refraction. | No, default: `1.5`|
+| **iorTexture** | [`textureInfo`](/specification/2.0/README.md#reference-textureInfo) | A greyscale texture that defines the index of refraction as 1/ior. | No |
+
+## Implementation
+
+The index of refraction affects the Fresnel term in the dielectric BRDF:
+
+```
+dielectric_brdf =
+  fresnel_mix(
+    diffuse_brdf(baseColor),
+    microfacet_brdf(roughness^2),
+    ior)
+```
+
+In case `KHR_materials_transmission` is enabled, the index of refraction also affects the refraction of light rays passing through the transparent surface.

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."
+        },
+        "iorTexture": {
+            "allOf": [ { "$ref": "textureInfo.schema.json" } ],
+            "description": "A greyscale texture that defines the index of refraction.",
+            "gltf_detailedDescription": "The texture stores the inverse of the index of refraction (1/ior) to keep the values in the range 0 to 1."
+        },
+        "extensions": { },
+        "extras": { }
+    }
+}