[x3d-public] How to implement glTF EXT_mesh_gpu_instancing?!

[Joe D Williams]

Thanks Holger.
I am finally learning to use Playground.
Joe
-----Original Message-----
From: Extensible 3D (X3D) Graphics public discussion <x3d-public at web3d.org>
Sent: Apr 21, 2024 4:36 AM
To: X3D <x3d-public at web3d.org>
Cc: Holger Seelig <holger.seelig at yahoo.de>
Subject: [x3d-public] How to implement glTF EXT_mesh_gpu_instancing?!

How to implement glTF EXT_mesh_gpu_instancing?!
 
When looking through the glTF sample models, sooner or later you will stumble across an example and this extension.
 
https://github.com/KhronosGroup/glTF/tree/main/extensions/2.0/Vendor/EXT_mesh_gpu_instancing
https://github.com/KhronosGroup/glTF-Sample-Models/tree/main/2.0/SimpleInstancing
 
The simplest idea to implement this, which I did, was to generate a lot of Transform nodes (one for each instance) and clone the shapes or geometry nodes. But this runs counter to the name of the extension (GPU). Especially if you create thousands of transform nodes for a shape with a geometry with only a few polygons. The extension is made to clone a lot of objects, e.g. a leaf on a tree, which then reappears in many places on the tree, only with different transformations, and everything should be calculated in one pass by the GPU.
 
The second idea I had was to somehow incorporate the transformations (translation, rotation, scale) for each instance into the X3DGeometryNode nodes. However, this would have meant changing all of these nodes. So I discarded this for the time being and postponed it.
 
Then I came up with the idea of why add it to the geometry nodes when you could invent a new shape node. So the idea of "InstancedShape" grew:
 
Documentation of InstancedShape in X_ITE with example at the bottom of the page (2500 instances, 2,160,040 triangles):
https://create3000.github.io/x_ite/components/x-ite/instancedshape/
 
InstancedShape : X3DShapeNode {
   # ... inherited fields
   MFVec3f [in,out] translations [] #
   MFRotation [in,out] rotations [] # list of rotations, one for each instance
   MFVec3f [in,out] scales [] # list of scales, one for each instance
   # List of translations, rotations, scales; one for each instance.
   # If only one value is provided, it is provided to each instance equivalently.
}
 
The advantage is that the geometry nodes do not have to be changed, and the same functions could be used to implement these nodes that were already available for ParticleSystem nodes with some trivial additions.
 
Examples to see InstancedShape node in action, all files are in glTF or GLB format converted to X3D:
 
Simple Instancing (125 instances, 1,500 triangles):
https://create3000.github.io/x_ite/playground/?url=https://raw.githubusercontent.com/KhronosGroup/glTF-Sample-Models/master/2.0/SimpleInstancing/glTF/SimpleInstancing.gltf
 
Teapots Galore (958 instances, 7,725,314 triangles):
https://create3000.github.io/x_ite/playground/?url=https://raw.githubusercontent.com/KhronosGroup/glTF/main/extensions/2.0/Vendor/EXT_mesh_gpu_instancing/samples/teapots_galore/teapots_galore.gltf
 
Fur Instancing (10,000 instances, 3,200,000 triangles):
https://create3000.github.io/x_ite/playground/?url=https://create3000.github.io/media/glTF/FurInstancing/FurInstancing.glb
 
3D Tiles (10 instances, 120 triangles):
https://create3000.github.io/x_ite/playground/?url=https://raw.githubusercontent.com/CesiumGS/3d-tiles-samples/main/glTF/GpuInstancesMetadata/GpuInstancesMetadata.gltf
 
Forest (100 instances, 21,400 triangles):
https://create3000.github.io/x_ite/playground/?url=https://raw.githubusercontent.com/bertt/cesium_3dtiles_samples/master/samples/1.1/forest/forest.glb
 
How do you do that, do you? Maybe we could consider this for a future X3D version.
 
Make X3D even better!
Best regards,
Holger
 
--
Holger Seelig
Leipzig, Germany
 
holger.seelig at yahoo.de
https://create3000.github.io/x_ite/









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