EXT_texture_avif

extensions/2.0/Vendor/EXT_texture_avif/README.md

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+# EXT_texture_avif
+
+## Contributors
+
+- Leon Radley, [@leon](https://github.com/leon)
+- Don McCurdy, [@donmccurdy](https://github.com/donmccurdy)
+- Alexey Knyazev, [@lexaknyazev](https://github.com/lexaknyazev)
+
+## Status
+
+Draft
+
+## Dependencies
+
+Written against the glTF 2.0 spec.
+
+## Overview
+
+This extension allows glTF models to use AVIF as a valid image format. A client that does not implement this extension can ignore the provided AVIF image and continue to rely on the PNG and JPG textures available in the base specification. Defining a fallback texture is optional. The [best practices](#best-practices) section describes the intended use case of this extension and the expected behavior when using it without a fallback texture.
+
+AVIF is an image format developed by the The Alliance for Open Media.
+
+## glTF Schema Updates
+
+The `EXT_texture_avif` extension is added to the `textures` node and specifies a `source` property that points to the index of the `images` node which in turn points to the AVIF image.
+
+The following glTF will load `image.avif` in clients that support this extension, and otherwise fall back to `image.png`.
+
+```
+"textures": [
+    {
+        "source": 0,
+        "extensions": {
+            "EXT_texture_avif": {
+                "source": 1
+            }
+        }
+    }
+],
+"images": [
+    {
+        "uri": "image.png"
+    },
+    {
+        "uri": "image.avif"
+    }
+]
+```
+
+When used in the glTF Binary (.glb) format the `images` node that points to the AVIF image uses the `mimeType` value of `image/avif`.
+
+```
+"textures": [
+    {
+        "source": 0,
+        "extensions": {
+            "EXT_texture_avif": {
+                "source": 1
+            }
+        }
+    }
+],
+"images": [
+    {
+        "mimeType": "image/png",
+        "bufferView": 1
+    },
+    {
+        "mimeType": "image/avif",
+        "bufferView": 2
+    }
+]
+```
+
+### JSON Schema
+
+[glTF.EXT_texture_avif.schema.json](schema/glTF.EXT_texture_avif.schema.json)
+
+## Best Practices
+
+Since AVIF is not as widely supported as JPEG and PNG, until [browser support](https://caniuse.com/avif) is good you will have to create a separate version of your asset with this extension and then do feature detection to load the avif version.
+AVIF has support for image sequences much like GIF, but this extension is only targeting using AVIF as a replacement for jpeg and png.
+When a fallback image is defined, this extension should not be present in `extensionsRequired`. This will allow all clients to render the glTF correctly, and those that support this extension can request the optimized AVIF version of the textures.
+
+### Using Without a Fallback
+
+To use AVIF images without a fallback, define `EXT_texture_avif` in both `extensionsUsed` and `extensionsRequired`. The `texture` node will then have only an `extensions` property as shown below.
+
+```
+"textures": [
+    {
+        "extensions": {
+            "EXT_texture_avif": {
+                "source": 1
+            }
+        }
+    }
+]
+```
+
+If a glTF contains a AVIF with no fallback texture and the browser does not support AVIF, the client should either display an error or decode the AVIF image at runtime (see [resource](#resources) for decoding libraries).
+
+## Known Implementations
+
+## Resources
+
+- [AVIF specification](https://aomediacodec.github.io/av1-avif/)
+- [AVIF reference implementation](https://github.com/AOMediaCodec/libavif/).
+- [Can I Use Browser Support](https://caniuse.com/avif)
+- [Sharp](https://sharp.pixelplumbing.com/) is a NodeJS library for fast encode/decode of AVIF using native modules (built on top of libvips which has support for AVIF.

extensions/2.0/Vendor/EXT_texture_avif/schema/glTF.EXT_texture_webp.schema.json

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+{
+  "$schema": "http://json-schema.org/draft-04/schema",
+  "title": "EXT_texture_avif glTF extension",
+  "type": "object",
+  "description": "glTF extension to specify textures using the AVIF image format.",
+  "allOf": [{ "$ref": "glTFProperty.schema.json" }],
+  "properties": {
+    "source": {
+      "allOf": [{ "$ref": "glTFid.schema.json" }],
+      "description": "The index of the images node which points to a AVIF image."
+    },
+    "extensions": {},
+    "extras": {}
+  }
+}