Merge pull request #1691 from ultrafishotoy/KHR_instancing

EXT_mesh_gpu_instancing

extensions/2.0/Vendor/EXT_mesh_gpu_instancing/README.md

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+# EXT\_mesh\_gpu\_instancing
+
+## Contributors
+
+* John Cooke, OTOY, <mailto:[email protected]>
+* Don McCurdy
+* Arseny Kapoulkine 
+
+## Acknowledgments
+
+## Status
+
+Experimental
+
+## Dependencies
+
+Written against the glTF 2.0 spec.
+
+## Overview
+
+This extension is specfically designed to enable GPU instancing which renders many copies of a single mesh at once using a small number of draw calls.  It's useful for things 
+like trees, grass, road signs, etc.  The TRANSLATION, ROTATION, and SCALE attributes allows the mesh to be displayed at many different locations with different rotations and scales.  
+Custom attributes can use the underscore mechanism to achieve other effects (i.e. _ID, _TRANSFORM4x3, etc.).
+
+## Extending Nodes with per instance attributes
+
+Instancing is defined by adding the `EXT_mesh_gpu_instancing` extension to any glTF node that has a mesh.  Instancing only applies to mesh nodes, there is no defined behavior for a node 
+with this extension that doesn't also have a mesh.  Applying to nodes rather than meshes allows the same mesh to be used by several nodes, instanced or otherwise.  The attributes 
+section contains accessor ids for the TRANSLATION, ROTATION, and SCALE attribute buffers, all of which are optional.  The attributes specify an object space transform that should be 
+multipled by the node's world transform in the shader to produce the final world transform for the instance. For example, the following defines some instancing attributes to a node with mesh.  
+
+```json
+{
+    "nodes": [
+        {
+            "mesh": 0,
+            "name": "teapot",
+            "extensions": {
+                "EXT_mesh_gpu_instancing": {
+                    "attributes": {
+                        "TRANSLATION": 0,
+                        "ROTATION": 1,
+                        "SCALE": 2,
+                        "_ID" : 3
+                    },
+                }
+            }
+        }
+    ]
+}
+```
+
+## Appendix
+
+
+## Reference
+
+
+### Theory, Documentation and Implementations