Support for non-indexed and interleaved geometry

[donmccurdy]

The renderer currently fails silently if given the following types of input geometry:

• non-indexed (or mixed index and non-indexed?)
• interleaved attributes
• mixed component types (e.g. some positions uint8, others uint16)

The error seems to be related to the mergeBufferGeometries step, which displays an error in the console. I'm not sure if it's possible to proceed without merging? three.js does have a mergeVertices utility that can help with creating an index. The other two (de-quantizing, de-interleaving) would require some custom code here.

I'm wondering if it would be an option to pre-process the input glTF file with gltf-transform, to normalize the structure for the path tracer, like:

import { WebIO, VertexLayout } from '@gltf-transform/core';
import { ALL_EXTENSIONS } from '@gltf-transform/extensions';
import { weld, dequantize } from '@gltf-transform/functions';

const io = new WebIO()
  .registerExtensions(ALL_EXTENSIONS)
  .setVertexLayout(VertexLayout.SEPARATE);

// Read.
const document = io.readBinary(inputGLB /* ArrayBuffer */);

// Process.
await document.transform(
  weld(),
  dequantize()
);

// Write.
const outputGLB = io.writeBinary(document);

^the dequantize function doesn't yet exist, but I could add it if that's of interest.

[bsdorra]

Merging is currently necessary. The BVH generation and the renderer expect a continuous, homogenous and non-indexed representation of the scenes geometry. Not very flexible or memory efficient, but it reduces the complexity when fetching the triangle data from a sampler in the pathtracing shader. Using mergeBufferGeometries (including its limitations) is the result of my laziness to write a proper custom translation, happy to get rid of it.

gltf-transform as preprocess to transform the data into the expected form sounds great. But, as I need to disentangle the interleaved meshes anyways, I could also add dequantization... Conversely, does (de-)interleaving (vertex-)data sound like a useful functionality to have in gltf-transform?

[donmccurdy]

Conversely, does (de-)interleaving (vertex-)data sound like a useful functionality to have in gltf-transform?

That's already available, added because some loaders don't support interleaved data. three.js supports interleaving of course, but certain packages (including three-mesh-bvh, until recently) don't, and so the option is configurable when writing a document with gltf-transform:

import { WebIO, VertexLayout } from '@gltf-transform/core';
import { ALL_EXTENSIONS } from '@gltf-transform/extensions';

const io = new WebIO()
  .registerExtensions(ALL_EXTENSIONS)
  .setVertexLayout(VertexLayout.SEPARATE); // INTERLEAVED (default) or SEPARATE

const outputGLB = io.writeBinary(document);

Perhaps there's a better term for it than 'separate'. 😅

[bsdorra]

Added gltf-transform to pre-process the input. Works as expected. Thanks for the report, and gltf-transform of course! ;) I'll open a new issue to track "support" for KHR_mesh_quantization

[donmccurdy]

Awesome, that was quick! I think the dequantize() function will be a pretty quick addition. I've started a PR in https://github.com/donmccurdy/glTF-Transform/pull/431.