EXT_property_animation extension proposal

extensions/2.0/Vendor/EXT_property_animation/README.md

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+# EXT\_property\_animation
+
+## Contributors
+
+* Bryce Hutchings, Microsoft [@brycehutchings](https://twitter.com/brycehutchings)
+* Gary Hsu, Microsoft [@bghgary](https://twitter.com/bghgary)
+* Jamie Marconi, Microsoft [@najadojo](https://twitter.com/najadojo)
+* Lewis Weaver, Microsoft
+
+## Status
+
+Draft
+
+## Dependencies
+
+Written against the glTF 2.0 spec.
+
+## Overview
+
+This extension adds a specification for animation data targeting arbitrary
+properties, such as material colors, texture transform matrices and
+extension properties.
+
+## Extending Animations
+
+Property animations can be added to an animation by adding the
+`EXT_property_animation` extension to any glTF animation. For example, the
+following defines an animation with two channels that modify a material's
+baseColorFactor and roughnessFactor.
+```json
+"animations" : [
+    {
+        "channels" : [], 
+        "extensions" : {
+            "EXT_property_animation" : {
+                "channels" : [
+                    {
+                        "sampler" : 0,
+                        "target" : "/materials/1/pbrMetallicRoughness/roughnessFactor"
+                    },
+                    {
+                        "sampler" : 1,
+                        "target" : "/materials/1/pbrMetallicRoughness/baseColorFactor"
+                    }
+                ]
+            }
+        }, 
+        "samplers" : [
+            {
+                "input" : 6,
+                "interpolation" : "CUBICSPLINE",
+                "output" : 7
+            },
+            {
+                "input" : 8,
+                "interpolation" : "LINEAR",
+                "output" : 9
+            }
+        ]
+    }
+]
+ ```
+`EXT_property_animation` adds a channels list separate from the core
+specification's such that a different set of target values can be described.
+
+### sampler
+
+`sampler` has the same meaning and interpretation as the core specification's
+`sampler` property. The property animation keyframes are defined in the normal
+samplers list and the `sampler` reference indexes into this list for the
+enclosing animation.
+
+The sampler's output accessor type must match the targeted property's type.
+
+### target
+
+`target` is a [JSON Pointer](https://tools.ietf.org/html/rfc6901) in the glTF
+JSON specifying a leaf property value. The property need not be present in the
+original JSON; default or implicit properties can be animated. `target` must
+reference a leaf property on an object that fits the data types supported by
+accessor elements. These types are `MAT4`, `MAT3`, `MAT2`, `VEC4`, `VEC3`,
+`VEC2`, and `SCALAR`. Properties that don't fit these data types cannot be
+animated. Animation of boolean or enum values is prevented as well as any
+indexed object reference within the glTF JSON (i.e. a property animation can't
+describe the value `"material": 0` or a new vertex buffer accessor such as
+`"POSITION" : 4`).
+
+Because the [JSON Pointer](https://tools.ietf.org/html/rfc6901) is able to
+reference any JSON property `EXT_property_animation` allows animation of all
+current and future glTF extensions. The path value would simply include
+`/extensions/EXT_my_extension/my_property`.
+
+## Extension compatibility and fallback behavior
+
+When possible, authoring tools should define reasonable initial values
+for properties intended to be animated and mark the `EXT_property_animation`
+extension as optional. Models including the extension optionally will still
+render in all clients that support the core glTF 2.0 specification. Clients
+that do not support the extension will fallback to an un-animated initial
+state.
+
+## glTF Schema Updates
+
+* **JSON schema**: [animation.EXT_property_animation.schema.json](schema/animation.EXT_property_animation.schema.json)
+
+## Known Implementations
+
+* [Blender glTF 2.0 Exporter](https://github.com/najadojo/glTF-Blender-Exporter/compare/master...najadojo:EXT_property_animation)
+Experiment/Proof of concept to export material property animations.
+* [three.js](https://github.com/mrdoob/three.js/compare/dev...najadojo:EXT_property_animation)
+Experiment/Proof of concept to import material property animations.

extensions/2.0/Vendor/EXT_property_animation/schema/EXT_property_animation.channel.schema.json

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+{
+    "$schema": "http://json-schema.org/draft-04/schema",
+    "title": "Animation Channel",
+    "type": "object",
+    "description": "Targets an animation's sampler at a node's property.",
+    "allOf": [ { "$ref": "glTFProperty.schema.json" } ],
+    "properties": {
+        "sampler": {
+            "allOf": [ { "$ref": "glTFid.schema.json" } ],
+            "description": "The index of a sampler in this animation used to compute the value for the target.",
+            "gltf_detailedDescription": "The index of a sampler in this animation used to compute the value for the target."
+        },
+        "target": {
+            "description": "The JSON Pointer of the property to be animated.",
+            "gltf_detailedDescription": "Must reference a leaf property on an object that fits the data types supported by accessor elements; animation of boolean or enum values is prevented as well as any indexed object reference within the glTF JSON.",
+            "type": "string"
+        },
+        "extensions": { },
+        "extras": { }
+    },
+    "required": [ "sampler", "target" ]
+}

extensions/2.0/Vendor/EXT_property_animation/schema/animation.EXT_property_animation.schema.json

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+{
+    "$schema": "http://json-schema.org/draft-04/schema",
+    "title": "EXT_property_animation glTF extension",
+    "type": "object",
+    "description": "glTF extension for arbitrary animated properties.",
+    "allOf": [ { "$ref": "glTFProperty.schema.json" } ],
+    "properties": {
+        "channels": {
+            "type": "array",
+            "description": "An array of channels, each of which targets an animation's sampler at a property. Different channels of the same animation can't have equal targets.",
+            "items": {
+                "$ref": "EXT_property_animation.channel.schema.json"
+            },
+            "minItems": 1
+        },
+        "extensions": { },
+        "extras": { }
+    }
+}