first draft of bump extension.

extensions/2.0/Vendor/EXT_materials_bump/README.md

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+# EXT\_materials\_bump
+
+## Contributors
+
+- Ben Houston, Threekit [@bhouston](https://github.com/bhouston)
+
+Copyright 2023 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, Ratified by the Khronos Group
+
+## 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
+
+This extension adds one parameters to the metallic-roughness material: `bump`.
+
+`bump` allows users to perturb the surface normal via a bump map. The bump map is a grayscale texture, where the value of each texel represents the height of the surface at that texel. The height is then used to perturb the normal direction.
+
+## Extending Materials
+
+The `KHR_materials_bump` extension can be specified in the `extensions` property of the material:
+
+```json
+{
+ "materials": [
+ {
+ "extensions": {
+ "KHR_materials_bump": {
+ "bumpFactor": 0.5
+ }
+ }
+ }
+ ]
+}
+```
+
+Factor and texture are combined by multiplication to describe a single value.
+
+| |Type|Description|Required|
+|-|----|-----------|--------|
+| **bumpFactor** | `number` | The strength of the specular reflection. | No, default: `1.0`|
+| **bumpTexture** | [`textureInfo`](https://www.khronos.org/registry/glTF/specs/2.0/glTF-2.0.html#reference-textureinfo) | A texture that defines the strength of the specular reflection, stored in the alpha (`A`) channel. This will be multiplied by bumpFactor. | No |
+
+The `bump` parameters affect the normal used in `dielectric_brdf` of the glTF 2.0 metallic-roughness material.
+
+## Implementation
+
+*This section is non-normative.*
+
+The `bump` parameter is used to perturb the normal direction. The normal direction is perturbed by the value of the bump map at the texel corresponding to the fragment. The perturbed normal is then used in the `dielectric_brdf` function of the glTF 2.0 metallic-roughness material.
+
+** TODO Derive Normal from Bump **
+
+In order to properly blend the bump map with a normal map, please follow the recommendation of https://blog.selfshadow.com/publications/blending-in-detail/.
+
+```glsl
+vec3 t = originalNormal.xyz * vec3( 2, 2, 2 ) + vec3( -1, -1, 0 );
+vec3 u = bumpNormal.xyz * vec3( -2, -2, 2 ) + vec3( 1, 1, -1 );
+vec3 r = normalize( t * dot(t, u) / t.z - u ); // not required if t and u are pre-normalized
+vec3 blendedNormal = r * 0.5 + 0.5;
+```
+
+## Schema
+
+- [material.KHR_materials_bump.schema.json](schema/material.KHR_materials_bump.schema.json)
+
+## Appendix: Full Khronos Copyright Statement
+
+Copyright 2023 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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+respective owners.

extensions/2.0/Vendor/EXT_materials_bump/schema/material.KHR_materials_bump.schema.json

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+{
+ "$schema": "http://json-schema.org/draft-04/schema",
+ "title": "KHR_materials_bump glTF Material Extension",
+ "type": "object",
+ "description": "glTF extension that defines a bump which perturbs the surface normal.",
+ "allOf": [ { "$ref": "glTFProperty.schema.json" } ],
+ "properties": {
+ "bumpFactor": {
+ "type": "number",
+ "description": "The strength of the bump displacement.",
+ "default": 1.0,
+ "minimum": 0.0,
+ "maximum": 1.0,
+ "gltf_detailedDescription": "This parameter scales the amount of normal perturbation by the bump map on the surface normal."
+ },
+ "bumpTexture": {
+ "allOf": [ { "$ref": "textureInfo.schema.json" } ],
+ "description": "A texture that defines the displacement in the alpha channel.",
+ "gltf_detailedDescription": "A texture that defines the displacement in the alpha channel. This will be multiplied by bumpFactor."
+ },
+ "extensions": { },
+ "extras": { }
+ }
+}