[Bug] glTF parser fails on non-indexed geometry and KHR_mesh_quantization

[nokonoko1203]

Module and/or Feature

@luma.gl/gltf - glTF parser (createScenegraphsFromGLTF)

Description

When loading 3D Tiles containing quantized point cloud data using Deck.gl's ScenegraphLayer, luma.gl throws an error.

There are two issues:

1. Non-indexed geometry not supported - glTF files without primitive.indices (such as point clouds) cause getVertexCount not implemented error because the function was never implemented.

2. 16-bit x3 vertex formats not supported - glTF files using the KHR_mesh_quantization extension with 16-bit x3 vertex formats (uint16x3, snorm8x3, etc.) cause errors.

Expected Behavior

The glTF parser should:

• Calculate vertex count from attributes when indices are not present
• Support WebGL-only 16-bit x3 vertex formats for KHR_mesh_quantization

Steps to Reproduce

1. Load a glTF/GLB file that:

   • Has no primitive.indices (non-indexed geometry), OR
   • Uses KHR_mesh_quantization extension with quantized vertex data
   • For example: [Bug] ScenegraphLayer: load quantized glb deck.gl#9213 (comment)

2. The glTF parser throws an error

Environment

• Framework version: luma.gl 9.x / deck.gl 9.x
• Browser: Any (WebGL backend)
• OS: Any

Logs

deck: initialization of ScenegraphLayer({id: '3d-tiles-scenegraph-[...]'}):
getVertexCount not implemented
Error: getVertexCount not implemented
    at GLTFInstantiator.getVertexCount
    at GLTFInstantiator.createPrimitive
    ...