Add SVG support for textures in GLTF specification

extensions/2.0/Vendor/EXT_texture_svg/README.md

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+# EXT_texture_svg
+
+## Contributors
+
+- K. S. Ernest (iFire) Lee, Godot Engine contributor, V-Sekai contributor.
+- Aaron Franke, The Mirror Megaverse Inc.
+
+## Status
+
+Draft
+
+## Dependencies
+
+Written against the glTF 2.0 spec.
+
+## Overview
+
+This extension allows glTF models to use SVG as a valid image format. A client that does not implement this extension can ignore the provided SVG 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.
+
+SVG is a vector image format that can be scaled to any size without loss of quality. SVG is supported by all major game engines and web browsers.
+
+SVG images are ideal for assets with simple shapes or text. For instance, a glTF asset like a billboard displaying a logo or a sign with substantial text would benefit from SVGs. This allows for clear visibility at any distance without the need for large raster images that increase file size.
+
+For non-vectorizable artwork, PNG and JPEG raster images can be embedded into SVG to allow for mixing vector shapes and text with complex detailed raster images.
+
+## glTF Schema Updates
+
+The `EXT_texture_svg` 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 SVG image.
+
+The following glTF will load `image.svg` in clients that support this extension, and otherwise fall back to `image.png`.
+
+```
+"textures": [
+    {
+        "source": 0,
+        "extensions": {
+            "EXT_texture_svg": {
+                "source": 1
+            }
+        }
+    }
+],
+"images": [
+    {
+        "uri": "image.png"
+    },
+    {
+        "uri": "image.svg"
+    }
+]
+```
+
+When used in the glTF Binary (.glb) format the `images` node that points to the SVG image uses the `mimeType` value of `image/svg+xml`.
+
+```
+"textures": [
+    {
+        "source": 0,
+        "extensions": {
+            "EXT_texture_svg": {
+                "source": 1
+            }
+        }
+    }
+],
+"images": [
+    {
+        "mimeType": "image/png",
+        "bufferView": 1
+    },
+    {
+        "mimeType": "image/svg+xml",
+        "bufferView": 2
+    }
+]
+```
+
+### JSON Schema
+
+[texture.EXT_texture_svg.schema.json](schema/texture.EXT_texture_svg.schema.json)
+
+## Best Practices
+
+SVG images are a great choice for images with simple shapes and images with text. For example, a glTF asset with a billboard that displays a simple logo with text would strongly benefit from SVG images, or a glTF asset with a sign with a lot of text would want to use SVG to allow for sharp text at any distance without having to use a large raster image that would greatly increase the file size.
+
+Since SVG is not a part of the base glTF spec, it is recommended to provide a raster image fallback for clients that do not support this extension. The fallback image should be high enough of a resolution that the text is still legible.
+
+The SVG format has a variety of features, not all of which are supported by all SVG implementations. If a client does not support a feature used in the SVG image, it should fall back to the raster image.
+
+Support for animated SVGs is not typically found in target glTF implementations.
+
+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 read the SVG version of the textures.
+
+### Using Without a Fallback
+
+To use SVG images without a fallback, define `EXT_texture_svg` in both `extensionsUsed` and `extensionsRequired`. The `texture` node will then have only an `extensions` property as shown below.
+
+```
+"textures": [
+    {
+        "extensions": {
+            "EXT_texture_svg": {
+                "source": 1
+            }
+        }
+    }
+]
+```
+
+If a glTF contains a SVG with no fallback texture, `EXT_texture_svg` should be added to the `extensionsRequired` array, such that clients that do not support SVG will not attempt to load the file.
+
+## Known Implementations
+
+None
+
+## Resources
+
+- https://en.wikipedia.org/wiki/SVG
+- https://developer.mozilla.org/en-US/docs/Web/SVG
+- https://www.w3.org/TR/SVG/

extensions/2.0/Vendor/EXT_texture_svg/schema/texture.EXT_texture_svg.schema.json

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