Very early draft of the gaussian splatting extension.

extensions/2.0/Khronos/KHR_gaussian_splatting/README.md

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+<!--
+Copyright 2015-2021 The Khronos Group Inc.
+SPDX-License-Identifier: CC-BY-4.0
+-->
+
+# CESIUM_gaussian_splatting
+
+## Contributors
+
+Jason Sobotka, Cesium
+Aras P.
+
+## Status
+
+Draft
+
+## Dependencies
+
+Written against the glTF 2.0 spec.
+
+## Overview
+
+Gaussian splats are currently stored in mostly unstructured files. This extension is an attempt to bring them to glTF and offer a structured, efficient method for streaming and rendering them.
+
+This method uses textures to store data for efficient GPU loading.
+
+Data formats within textures:
+ * Positions (R10G10B10A2 good default),
+ * Rotations (always R10G10B10A2),
+ * Scales (R5G6B5 good default),
+ * Color+opacity (R8G8B8A8 is easy),
+
+## Sample
+
+Extending glTF node:
+
+```
+{
+    "accessors": [
+        {
+            "type": "VEC3",
+            "componentType": "FLOAT" // Enum
+        },
+        {
+            "type": "VEC4",
+            "componentType": "UNSIGNED_BYTE", // Enum
+            "normalized": true
+        },
+        {
+            "type": "VEC4", // quaternion
+            "componentType": "FLOAT" // could be quantized with KHR_mesh_quantization + EXT_meshopt_compression
+        },
+        {
+            "type": "VEC3",
+            "componentType": "FLOAT" // could be quantized with KHR_mesh_quantization + EXT_meshopt_compression
+        }
+    ],
+    "meshes": [
+        {
+            "primitives": [
+                {
+                    "mode": 0, // POINT CLOUD
+                    "attributes": {
+                        "POSITION": 0,
+                        "COLOR_0": 1,
+                        "_ROTATION": 2,
+                        "_SCALE": 3
+                    },
+                    "extensions": {
+                        "CESIUM_gaussian_splats": {
+                            // May need to consider spherical harmonics in the future. Separate extension?
+                            // Quantization scale for additional attributes goes here if needed
+                        }
+                    }
+                }
+            ]
+        }
+    ]
+}
+```
+
+### JSON Schema
+
+TODO: Links to the JSON schema for the new extension properties.
+
+## Implementation Notes
+
+This doesn't specify any specific rendering techniques. This is purely for organizing the data in a structured manner.
+
+## Resources
+
+https://github.com/mkkellogg/GaussianSplats3D/issues/47#issuecomment-1801360116