Merge branch 'main' into 3d-tiles-next

Author: lilleyse

.github/workflows/CI.yml

@@ -23,7 +23,7 @@ jobs:
 
     steps:
       # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
 
       # Build spec targets
       - name: spec-generate
@@ -32,7 +32,7 @@ jobs:
           make Specification.html Specification.pdf
 
       - name: Archive generated files
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v4
         with:
           name: spec-outputs
           path: |

README.md

@@ -7,8 +7,9 @@ SPDX-License-Identifier: CC-BY-4.0
 <img src="specification/figures/glTF_RGB_June16.svg" width="340" height="170" />
 </p>
 
-[![Join the Slack group](https://img.shields.io/badge/chat-on%20slack-blue.svg)](https://www.khr.io/slack)
+[![Join glTF Discord](https://img.shields.io/badge/discuss-on%20discord-blue.svg)](https://khr.io/khrdiscord)
 [![Join the forums](https://img.shields.io/badge/discuss-in%20forums-blue.svg)](https://community.khronos.org/c/gltf-general)
+[![Join the Slack group](https://img.shields.io/badge/chat-on%20slack-blue.svg)](https://www.khr.io/slack)
 
 glTF™ (GL Transmission Format) is a royalty-free specification for the efficient transmission and loading of 3D scenes and models by applications. glTF minimizes both the size of 3D assets, and the runtime processing needed to unpack and use those assets. glTF defines an extensible, common publishing format for 3D content tools and services that streamlines authoring workflows and enables interoperable use of content across the industry.
 

extensions/2.0/Khronos/KHR_animation_pointer/README.md

@@ -20,7 +20,7 @@ See [Appendix](#appendix-full-khronos-copyright-statement) for full Khronos Copy
 
 ## Status
 
-Release Candidate
+Complete, Ratified by the Khronos Group
 
 ## Dependencies
 

extensions/2.0/Khronos/KHR_materials_anisotropy/README.md

@@ -64,18 +64,24 @@ Sample values:
 
 |                         | Type     | Description               | Required           |
 | ----------------------- | -------- | ------------------------- | ------------------ |
-| **anisotropyStrength**  | `number` | The anisotropy strength. When anisotropyTexture is present, this value is multiplied by the blue channel. | No, default: `0.0` |
-| **anisotropyRotation**  | `number` | The rotation of the anisotropy in tangent, bitangent space, measured in radians counter-clockwise from the tangent. When anisotropyTexture is present, anisotropyRotation provides additional rotation to the vectors in the texture. | No, default: `0.0` |
-| **anisotropyTexture**   | [`textureInfo`](https://registry.khronos.org/glTF/specs/2.0/glTF-2.0.html#reference-textureinfo) | The anisotropy texture. Red and green channels represent the anisotropy direction in [-1, 1] tangent, bitangent space, to be rotated by anisotropyRotation. The blue channel contains strength as [0, 1] to be multiplied by anisotropyStrength. | No |
+| **anisotropyStrength**  | `number` | The anisotropy strength. When the anisotropy texture is present, this value is multiplied by the texture's blue channel. | No, default: `0.0` |
+| **anisotropyRotation**  | `number` | The rotation of the anisotropy in tangent, bitangent space, measured in radians counter-clockwise from the tangent. When the anisotropy texture is present, this value provides additional rotation to the vectors in the texture. | No, default: `0.0` |
+| **anisotropyTexture**   | [`textureInfo`](https://registry.khronos.org/glTF/specs/2.0/glTF-2.0.html#reference-textureinfo) | The anisotropy texture. Red and green channels represent the anisotropy direction in $[-1, 1]$ tangent, bitangent space to be rotated by the anisotropy rotation. The blue channel contains strength as $[0, 1]$ to be multiplied by the anisotropy strength. | No |
 
 ## Anisotropy
 
 Two new material properties are introduced: a strength parameter and the direction in which the specular reflection elongates relative to the surface tangents.
-The strength parameter is a dimensionless number in the range `[0, 1]` and increases the roughness along a chosen direction. The default direction aligns with the tangent to the mesh as described in the glTF 2.0 specification, [Meshes section](https://registry.khronos.org/glTF/specs/2.0/glTF-2.0.html#meshes).
+The strength parameter is a dimensionless number in the range $[0, 1]$ and increases the roughness along a chosen direction. The default direction aligns with the tangent to the mesh as described in the glTF 2.0 specification, [Meshes section](https://registry.khronos.org/glTF/specs/2.0/glTF-2.0.html#meshes).
 
-All meshes with materials that use anisotropy **SHOULD** supply `TANGENT` vectors as a mesh attribute.  If `TANGENT` vectors are not supplied for such a mesh, the mesh **MUST** supply a `normalTexture`, and tangents are computed according to rules in the [Meshes section](https://registry.khronos.org/glTF/specs/2.0/glTF-2.0.html#meshes) of the glTF specification. Likewise when `TANGENT` vectors are not supplied for a mesh, the mesh **MUST NOT** supply different texture coordinates on the `normalTexture` and `anisotropyTexture`.
+A mesh primitive using an anisotropy material **MUST** have a defined tangent space, i.e., it **MUST** have `NORMAL` and `TANGENT` attributes or its base material **MUST** have a normal texture. When the mesh primitive does not have `NORMAL` or `TANGENT` vectors, they are computed as defined in the glTF 2.0 specification.
 
-The `anisotropyTexture`, when supplied, encodes XY components of the direction vector in tangent space as red and green values, and strength as blue values, all stored with linear transfer function. After dequantization, red and green texel values **MUST** be mapped as follows: red [0.0 .. 1.0] to X [-1 .. 1], green [0.0 .. 1.0] to Y [-1 .. 1].  Blue does not require remapping.  When `anisotropyTexture` is not supplied, the default value is red 1.0 (X 1.0), green 0.5 (Y 0.0), and blue 1.0 (strength 1.0).  The direction of this XY vector specifies the per-texel direction of increased anisotropy roughness in tangent, bitangent space, prior to being rotated by `anisotropyRotation`.  The blue channel contains strength as [0.0 .. 1.0] to be multiplied by `anisotropyStrength` to determine the per-texel anisotropy strength.
+Since the glTF 2.0 specification does not mandate any particular tangent space derivation algorithm, mesh primitives using anisotropy materials **SHOULD** always provide their `NORMAL` and `TANGENT` vectors.
+
+When the material has both `normalTexture` and `anisotropyTexture` properties defined, these textures **SHOULD** use the same texture coordinates because they operate in the same tangent space and their texel values are usually correlated to each other.
+
+The anisotropy texture, when supplied, encodes XY components of the anisotropy direction vector in tangent space as red and green values, and the anisotropy strength as blue values, all stored with linear transfer function. After dequantization, red and green texel values **MUST** be mapped as follows: red $[0, 1]$ to X $[-1, 1]$, green $[0, 1]$ to Y $[-1, 1]$.  Blue does not require remapping.  When the anisotropy texture is not supplied, the default dequantized texel value is $(1.0; 0.5; 1.0)$, which corresponds to the $(1; 0)$ direction vector (+X axis) and full strength.
+
+The direction of this XY vector specifies the per-texel direction of increased anisotropy roughness in tangent, bitangent space, prior to being rotated by the `anisotropyRotation` property value.  After dequantization, the blue channel contains strength as $[0, 1]$ to be multiplied by the `anisotropyStrength` property value to determine the per-texel anisotropy strength.
 
 > **Note:** The direction vector of the anisotropy is the direction in which highlights will be stretched. The direction of the micro-grooves in the material causing the anisotropy will run perpendicular.
 

extensions/2.0/Khronos/KHR_materials_anisotropy/schema/material.KHR_materials_anisotropy.schema.json

@@ -11,18 +11,18 @@
             "default": 0.0,
             "minimum": 0.0,
             "maximum": 1.0,
-            "gltf_detailedDescription": "The anisotropy strength. When anisotropyTexture is present, this value is multiplied by the blue channel."
+            "gltf_detailedDescription": "The anisotropy strength. When the anisotropy texture is present, this value is multiplied by the texture's blue channel."
         },
         "anisotropyRotation": {
             "type": "number",
             "description": "The rotation of the anisotropy.",
             "default": 0.0,
-            "gltf_detailedDescription": "The rotation of the anisotropy in tangent, bitangent space, measured in radians counter-clockwise from the tangent. When anisotropyTexture is present, anisotropyRotation provides additional rotation to the vectors in the texture."
+            "gltf_detailedDescription": "The rotation of the anisotropy in tangent, bitangent space, measured in radians counter-clockwise from the tangent. When the anisotropy texture is present, this value provides additional rotation to the vectors in the texture."
         },
         "anisotropyTexture": {
             "allOf": [ { "$ref": "textureInfo.schema.json" } ],
             "description": "The anisotropy texture.",
-            "gltf_detailedDescription": "The anisotropy texture. Red and green channels represent the anisotropy direction in [-1, 1] tangent, bitangent space, to be rotated by anisotropyRotation. The blue channel contains strength as [0, 1] to be multiplied by anisotropyStrength."
+            "gltf_detailedDescription": "The anisotropy texture. Red and green channels represent the anisotropy direction in $[-1, 1]$ tangent, bitangent space, to be rotated by the anisotropy rotation. The blue channel contains strength as $[0, 1]$ to be multiplied by the anisotropy strength."
         },
         "extensions": { },
         "extras": { }

extensions/2.0/Khronos/KHR_materials_clearcoat/README.md

@@ -77,6 +77,12 @@ clearcoatRoughness = clearcoatRoughnessFactor * clearcoatRoughnessTexture.g
 
 If `clearcoatNormalTexture` is not given, no normal mapping is applied to the clear coat layer, even if normal mapping is applied to the base material.  Otherwise, `clearcoatNormalTexture` may be a reference to the same normal map used by the base material, or any other compatible normal map.
 
+A mesh primitive using a clearcoat material with a clearcoat normal texture **MUST** have a defined tangent space, i.e., it **MUST** have `NORMAL` and `TANGENT` attributes or its base material **MUST** have a normal texture. When the mesh primitive does not have `NORMAL` or `TANGENT` vectors, they are computed as defined in the glTF 2.0 specification.
+
+Since the glTF 2.0 specification does not mandate any particular tangent space derivation algorithm, mesh primitives using clearcoat materials with clearcoat normal textures **SHOULD** always provide their `NORMAL` and `TANGENT` vectors.
+
+When the material has both `normalTexture` and `clearcoatNormalTexture` properties defined, these textures **SHOULD** use the same texture coordinates because they operate in the same tangent space and their texel values are usually correlated to each other.
+
 The clearcoat effect is modeled via a microfacet BRDF. The BRDF is layered on top of the glTF 2.0 Metallic-Roughness material, including emission and all extensions, using a new `fresnel_coat` function:
 
 ```
@@ -117,35 +123,33 @@ The `fresnel_coat` function is computed using the Schlick Fresnel term from the
 ```
 function fresnel_coat(normal, ior, weight, base, layer) {
   f0 = ((1-ior)/(1+ior))^2
-  fr = f0 + (1 - f0)*(1 - abs(NdotV))^5   // N = normal
+  fr = f0 + (1 - f0)*(1 - abs(dot(V, normal)))^5
   return mix(base, layer, weight * fr)
 }
 ```
 
 Applying the functions we arrive at the coated material
 
 ```
-coated_material = mix(material, clearcoat_brdf(clearcoatRughness^2), clearcoat * (0.04 + (1 - 0.04) * (1 - NdotV)^5))
+coated_material = mix(material, clearcoat_brdf(clearcoatRoughness^2), clearcoat * (0.04 + (1 - 0.04) * (1 - VdotNc)^5))
 ```
 
 and finally, substituting and simplifying, using some symbols from [Appendix B](https://www.khronos.org/registry/glTF/specs/2.0/glTF-2.0.html#appendix-b-brdf-implementation) and `Nc` for the clearcoat normal:
 
 ```
-clearcoatFresnel = 0.04 + (1 - 0.04) * (1 - abs(VdotNc))^5
-clearcoatAlpha = clearcoatRoughness^2
-
-f_clearcoat = clearcoatFresnel * D(clearcoatAlpha) * G / (4 * abs(VdotNc) * abs(LdotNc))
+clearcoat_fresnel = 0.04 + (1 - 0.04) * (1 - abs(VdotNc))^5
+clearcoat_alpha = clearcoatRoughness^2
+clearcoat_brdf = D(clearcoat_alpha) * G(clearcoat_alpha) / (4 * abs(VdotNc) * abs(LdotNc))
 
-coated_material = (f_diffuse + f_specular) * (1 - clearcoat * clearcoatFresnel) +
-                  f_clearcoat * clearcoat
+coated_material = mix(material, clearcoat_brdf, clearcoat * clearcoat_fresnel)
 ```
 
 #### Emission
 
 The clearcoat layer is on top of emission in the layering stack. Consequently, the emission is darkened by the Fresnel term.
 
 ```
-coated_emission = emission * (0.04 + (1 - 0.04) * (1 - NdotV)^5)
+coated_emission = emission * (1 - clearcoat * clearcoat_fresnel)
 ```
 
 #### Discussion

extensions/2.0/Khronos/KHR_materials_dispersion/README.md

@@ -16,7 +16,7 @@ See [Appendix](#appendix-full-khronos-copyright-statement) for full Khronos Copy
 
 ## Status
 
-Release Candidate
+Complete, Ratified by the Khronos Group
 
 ## Dependencies
 

extensions/2.0/Khronos/KHR_materials_ior/README.md

@@ -47,7 +47,7 @@ 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.
+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 extension allows users to set the index of refraction to a certain value.
 
 ## Extending Materials
 
@@ -94,7 +94,21 @@ dielectric_brdf =
       α = roughness^2))
 ```
 
-Valid values for `ior` are numbers greater than or equal to 1. In addition, a value of 0 is allowed. This value gives full weight to `layer`, i.e., the Fresnel term evaluates to 1 independent of the view or light direction. It is useful in combination with `KHR_materials_specular` to seamlessly support the specular-glossiness workflow.
+Valid values for `ior` are numbers greater than or equal to one. As a special case, a value of zero is allowed as described below.
+
+### Specular-Glossiness Backwards Compatibility Mode
+
+Setting IOR to zero permanently switches the material into a special specular-glossiness backwards compatibility mode designed to ease content transition from the legacy specular-glossiness model (previously available via `KHR_materials_pbrSpecularGlossiness` extension) to the glTF 2.0 core metallic-roughness PBR model.
+
+This mode has the following implications:
+
+- The effective IOR becomes positive infinity and the Fresnel term **MUST** evaluate to `1.0` independently of the view or light direction.
+
+- All material features **MUST** treat IOR as having a very large value representing positive infinity, subject to numerical precision. For example, this would cause the `dispersion` property (as defined in `KHR_materials_dispersion`) to have no effect on the material appearance.
+
+- This mode cannot be toggled dynamically, e.g., with `KHR_animation_pointer` or `KHR_interactivity` extensions. If the IOR property is set to zero in JSON, glTF Asset Object Model updates of it **MUST** be ignored.
+
+- A value of zero (as well as any other value less than one) **MUST NOT** be used in an animation sampler targeting the IOR property, even if the IOR is set to zero in glTF JSON.
 
 ## Implementation
 
@@ -103,10 +117,10 @@ Valid values for `ior` are numbers greater than or equal to 1. In addition, a va
 The extension changes the computation of the Fresnel term defined in [Appendix B](https://www.khronos.org/registry/glTF/specs/2.0/glTF-2.0.html#appendix-b-brdf-implementation) to the following:
 
 ```
-const dielectricSpecular = ((ior - 1)/(ior + 1))^2
+dielectric_f0 = ((ior - 1)/(ior + 1))^2
 ```
 
-Note that for the default index of refraction `ior = 1.5` this term evaluates to `dielectricSpecular = 0.04`.
+Note that for the default index of refraction `ior = 1.5` this term evaluates to `dielectric_f0 = 0.04`.
 
 ## Interaction with other extensions
 

extensions/2.0/Khronos/KHR_materials_iridescence/README.md

@@ -76,13 +76,17 @@ iridescence = iridescenceFactor * iridescenceTexture.r
 
 If `iridescenceFactor` is zero (default), the iridescence extension has no effect on the material.
 All textures in this extension use a single channel in linear space.
-The thickness of the thin-film is set to `iridescenceThicknessMaximum` if `iridescenceThicknessTexture` is not given.
-If `iridescenceThicknessTexture` is set, the thickness of the thin-film varies between  `iridescenceThicknessMinimum` and `iridescenceThicknessMaximum` as follows:
+
+The thickness of the thin-film is defined by the `iridescenceThicknessMinimum`, `iridescenceThicknessMaximum`, and `iridescenceThicknessTexture` properties. The `iridescenceThicknessMinimum` and `iridescenceThicknessMaximum` values correspond to the sampled thickness texture values of 0.0 and 1.0 respectively, thus defining the effective range of the thin-film thickness as follows:
 
 ```glsl
 thickness = mix(iridescenceThicknessMinimum, iridescenceThicknessMaximum, iridescenceThicknessTexture.g)
 ```
 
+The `iridescenceThicknessMinimum` value **MAY** be greater than `iridescenceThicknessMaximum` value.
+
+If the thickness texture is not present, it is implicitly sampled as 1.0 so the thin-film thickness is uniformly set to the `iridescenceThicknessMaximum` value.
+
 Aside from light direction and IOR, the thickness of the thin-film defines the variation in hue.
 This effect is the result of constructive and destructive interferences of certain wavelengths.
 If the the optical path difference between the ray reflected at the thin-film and the ray reflected at the base material is half the wavelength (λ), the resulting 180 degree phase shift is cancelling out the reflected light:

extensions/2.0/Khronos/KHR_materials_iridescence/schema/material.KHR_materials_iridescence.schema.json

@@ -28,14 +28,14 @@
             "description": "The minimum thickness of the thin-film layer given in nanometers.",
             "default": 100.0,
             "minimum": 0.0,
-            "gltf_detailedDescription": "The minimum thickness of the thin-film layer given in nanometers. The value **MUST** be less than or equal to the value of `iridescenceThicknessMaximum`."
+            "gltf_detailedDescription": "The minimum thickness of the thin-film layer given in nanometers."
         },
         "iridescenceThicknessMaximum": {
             "type": "number",
             "description": "The maximum thickness of the thin-film layer given in nanometers.",
             "default": 400.0,
             "minimum": 0.0,
-            "gltf_detailedDescription": "The maximum thickness of the thin-film layer given in nanometers. The value **MUST** be greater than or equal to the value of `iridescenceThicknessMinimum`."
+            "gltf_detailedDescription": "The maximum thickness of the thin-film layer given in nanometers."
         },
         "iridescenceThicknessTexture": {
             "allOf": [ { "$ref": "textureInfo.schema.json" } ],