gltf_viewer crashes when loading a gltf with instanced meshes (EXT_mesh_gpu_instancing)

[achu-topshelf]

Does filament support gltf's EXT_mesh_gpu_instancing?
Not sure whether the parser used underneath gltfio (cgltf?) supports this extension?
If the support is not there, is it simple enough to add this in gltfio C++ lib?

A simple gltf file with two instanced boxes created with threejs:InstancedMesh() and exported as gltf (see attached file), crashes gltf_viewer sample app on Linux.
cube_instances.gltf.gz

gltf_viewer, of course, works fine on gltf that contains non-instanced meshes generated/exported with threejs.

The gltf file containing the instanced meshes renders fine in both https://gltf-viewer.donmccurdy.com/ and https://sandbox.babylonjs.com/

#0  std::__1::vector<filament::gltfio::FFilamentInstance*, std::__1::allocator<filament::gltfio::FFilamentInstance*> >::size[abi:v15007]() const (this=0x110) at /usr/lib/llvm-15/bin/../include/c++/v1/vector:547
#1  0x0000555556560a7c in filament::gltfio::FFilamentAsset::getAssetInstanceCount (this=0x0)
    at ../../libs/gltfio/src/FFilamentAsset.h:209
#2  0x000055555655f78d in filament::gltfio::FilamentAsset::getAssetInstanceCount (this=0x0)
    at ../../libs/gltfio/src/FilamentAsset.cpp:393
#3  0x0000555555649e09 in filament::gltfio::FilamentAsset::getInstance (this=0x0)
    at ../../libs/gltfio/include/gltfio/FilamentAsset.h:281
#4  0x000055555563a676 in main::$_9::operator() (this=0x7fffffffd258, filename=...)
    at ../../samples/gltf_viewer.cpp:557

555	        // Parse the glTF file and create Filament entities.
556	        app.asset = app.assetLoader->createAsset(buffer.data(), buffer.size());
557	        app.instance = app.asset->getInstance();
558	        buffer.clear();
559	        buffer.shrink_to_fit();
560	
561	        if (!app.asset) {
(gdb) p app.asset
$1 = (filament::gltfio::FilamentAsset *) 0x0

[achu-topshelf]

Comments by @romainguy in #3401 in 2021 indicate that EXT_mesh_gpu_instancing is not supported. Is this still true?

Also the code in filament/third_party/cgltf seems to have the code that parses EXT_mesh_gpu_instancing. But this is exactly the code that fails with:

read 1 "gltf_viewer" hit Breakpoint 1, filament::gltfio::FAssetLoader::createInstancedAsset (this=0x55555908e070, 
    bytes=0x555559982830 "{\"asset\":{\"version\":\"2.0\",\"generator\":\"THREE.GLTFExporter\"},\"scenes\":[{\"nodes\":[2]}],\"scene\":0,\"nodes\":[{\"matrix\":[1,0,0,0,0,1,0,0,0,0,1,0,0,50,0,1],\"mesh\":0,\"extensions\":{\"EXT_mesh_gpu_instancing\":{\""..., byteCount=3201, instances=0x7fffffffbde0, numInstances=1)
    at ../../libs/gltfio/src/AssetLoader.cpp:322
....
........
345	    cgltf_result result = cgltf_parse(&options, glbdata.data(), byteCount, &sourceAsset);
(gdb) n
346	    if (result != cgltf_result_success) {
(gdb) p result
$2 = cgltf_result_invalid_gltf

the error seems to be in

        # cgltf.h:6413
        if (data->nodes[i].has_mesh_gpu_instancing)
        {
            CGLTF_PTRFIXUP_REQ(data->nodes[i].mesh_gpu_instancing.buffer_view, data->buffer_views, data->buffer_views_count);
        ....
        ..........

where buffer_view is NULL.
I do not think that the problem is with my generated gltf since the reference assets at: https://github.com/KhronosGroup/glTF-Sample-Assets/tree/main/Models/SimpleInstancing also crashes gltf_viewer the same way.

[achu-topshelf]

I tried replacing filament/third_party/cgltf/cgltf*.h with the latest ones from the https://github.com/jkuhlmann/cgltf and at least the gltf with instances parses without crashing.
Just FYI on the gltf_viewer behavior with the replaced cgltf/cgltf*.h files, only a single instance of the mesh is rendered rather than all the instances. But this is expected since I did not do a merge of the above cgltf*.h files and downstream instance creation is not implemented in filament.

Would appreciate any gotchas/pointers from the filament maintainers on how to proceed to get the instanced meshes supported.