KHR_materials_emissive_strength

extensions/2.0/Khronos/KHR_materials_emissive_strength/README.md

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+# KHR\_materials\_emissive\_strength
+
+## Contributors
+
+* Mike Bond, Adobe, [@miibond](https://github.com/MiiBond)
+* Alex Jamerson, Amazon
+* Thomas Dideriksen, Amazon
+* Alex Wood, Analytical Graphics, [@abwood](https://twitter.com/abwood)
+* Ed Mackey, Analytical Graphics, [@emackey](https://twitter.com/emackey)
+* Nicolas Savva, Autodesk [@nicolassavva-autodesk](https://github.com/nicolassavva-autodesk)
+* Henrik Edstrom, Autodesk
+* Tobias Haeussler, Dassault Systemes [@proog128](https://github.com/proog128)
+* Bastian Sdorra, Dassault Systemes [@bsdorra](https://github.com/bsdorra)
+* Emmett Lalish, Google [@elalish](https://github.com/elalish)
+* Alexey Knyazev, Individual Contributor, [@lexaknyazev](https://github.com/lexaknyazev)
+* Bruce Cherniak, Intel
+* Gary Hsu, Microsoft [@bghgary](https://twitter.com/bghgary)
+* Nicholas Barlow, Microsoft
+* Adam Morris, Target [@weegeekps](https://github.com/weegeekps)
+* Sandra Voelker, Target
+* Ben Houston, Threekit, [@bhouston](https://twitter.com/BenHouston3D)
+* Eric Chadwick, Wayfair [echadwick-wayfair](https://github.com/echadwick-wayfair)
+
+Copyright (C) 2021 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
+
+Draft
+
+## Dependencies
+
+Written against the glTF 2.0 spec.
+
+## Exclusions
+
+* This extension must not be used on a material that also uses `KHR_materials_unlit`.
+
+## Overview
+
+The core glTF 2.0 material model includes an `emissiveFactor` and an `emissiveTexture` to control the color and
+intensity of the light being emitted by the material, clamped to the range [0.0, 1.0]. However, in PBR environments
+with high-dynamic range reflections and lighting, stronger emission effects may be desirable.
+
+In this extension, a new `emissiveStrength` scalar factor is supplied, that governs the upper limit of emissive
+strength per material.
+
+**Implementation Note**: This strength can be colored and tempered using the core material's `emissiveFactor`
+and `emissiveTexture` controls, permitting the strength to vary across the surface of the material.
+Supplying values above 1.0 for `emissiveStrength` can have an influence on
+reflections, tonemapping, blooming, and more.
+
+### Physical Units
+
+For implementations where a physical light unit is needed, the units for the multiplicative product of
+`emissiveStrength`, `emissiveFactor`, and `emissiveTexture` are candela per square
+meter (**cd / m<sup>2</sup>**), sometimes called *nits*.
+
+**Implementation Note**:
+Because the value is specified per square meter, it indicates the brightness of any given point along
+the surface.  However, the exact conversion from physical light units to the brightness of rendered
+pixels requires knowledge of the camera's exposure settings, which are left as an implementation
+detail, unless otherwise defined in a future version of the glTF specification or other extension.
+Many rendering engines simplify this calculation by assuming that an emissive factor of `1.0`
+results in a fully exposed pixel.
+
+## Extending Materials
+
+*This section is non-normative.*
+
+Any material with an `emissiveFactor` (and optionally an `emissiveTexture`) can have its strength modulated
+or amplified by the inclusion of this extension.  For example:
+
+```json
+{
+    "materials": [
+        {
+            "emissiveFactor": [
+                1.0,
+                1.0,
+                1.0
+            ],
+            "emissiveTexture": {
+                "index": 3
+            },
+            "extensions": {
+                "KHR_materials_emissive_strength": {
+                    "emissiveStrength": 5.0
+                }
+            }
+        }
+    ]
+}
+```
+
+In the above example, the `emissiveFactor` has been set to its maximum value, to enable the `emissiveTexture`.
+The `emissiveStrength` has been set to 5.0, making the texture five times brighter than it otherwise
+would have been.
+
+### Parameters
+
+The following parameters are contributed by the `KHR_materials_emissive_strength` extension:
+
+| Name                   | Type       | Description                                    | Required           |
+|------------------------|------------|------------------------------------------------|--------------------|
+| **emissiveStrength**   | `number`   | The maximum strength of the emissive texture.  | No, default: `1.0` |
+
+
+## Implementation Notes
+
+*This section is non-normative.*
+
+A typical (pseudocode) implementation might look like the following:
+
+```
+color += emissiveFactor.rgb * sRGB_to_Linear(emissiveTexture.rgb) * emissiveStrength;
+```
+
+## Schema
+
+- [glTF.KHR_materials_emissive_strength.schema.json](schema/glTF.KHR_materials_emissive_strength.schema.json)
+
+## Appendix: Full Khronos Copyright Statement
+
+Copyright 2021 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.
+
+Khronos makes no, and expressly disclaims any, representations or warranties,
+express or implied, regarding this specification, including, without limitation:
+merchantability, fitness for a particular purpose, non-infringement of any
+intellectual property, correctness, accuracy, completeness, timeliness, and
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+
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+of Hewlett Packard Enterprise used under license by Khronos. ASTC is a trademark of
+ARM Holdings PLC. All other product names, trademarks, and/or company names are used solely
+for identification and belong to their respective owners.

extensions/2.0/Khronos/KHR_materials_emissive_strength/schema/glTF.KHR_materials_emissive_strength.schema.json

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+{
+    "$schema": "http://json-schema.org/draft-04/schema",
+    "title": "KHR_materials_emissive_strength glTF extension",
+    "type": "object",
+    "description": "glTF extension that adjusts the strength of emissive material properties.",
+    "allOf": [ { "$ref": "glTFProperty.schema.json" } ],
+    "properties": {
+        "emissiveStrength": {
+            "type": "number",
+            "description": "The strength adjustment to be multiplied with the material's emissiveFactor and emissiveTexture.",
+            "default": 1.0,
+            "minimum": 0.0
+        },
+        "extensions": { },
+        "extras": { }
+    }
+}