Buffer to short when adding an indices accessor for a primitive

[Rennzie]

I've run into an issue trying to reprocess a LINES primitive to use indices instead of duplicate positions. I've removed the dup verts from the positions accessor and created a set of indices. I created a new accessor which I set to the primitive. I've reused the buffer referenced by the positions primitive when creating the indices accessor. The code looks like this:

const accessor = doc
      .createAccessor()
      .setBuffer(positions.getBuffer())
      .setType(AccessorTypes.SCALAR)
      .setArray(new Uint16Array(newIndices))
      .setName('indices');

linePrimitive.setIndices(accessor);

I then export the document as a .glb and run it through gltfpack. This errors out with Error: Error loading input.glb: buffer too short.

I've also tried adding a new buffer but when it comes to writing the .glb it errors with Error: GLB must have 0–1 buffers..

Is there something obvious I'm missing? Or is there a way to increase the size of the underlying buffer or merge two buffers before writing?

Any help would be greatly appreciated.

[donmccurdy]

The library includes a weld() function for computing indices, although I'm not sure I've tested it with LINES primitives yet. Could you try this?

import { weld } from '@gltf-transform/functions';

await document.transform(
  weld({tolerance: 1e-4})
);

If not, it might also be worth trying io.setVertexLayout(VertexLayout.SEPARATE) (before exporting the model) to see if that fixes whatever buffer layout issue is going on.

If none of that works, would you be able to share a sample input file?

[Rennzie]

Thanks for the quick response @donmccurdy. I'll give those a try and let you know how it goes.

[Rennzie]

Hey @donmccurdy, I tested the weld on my input.glb. Happy to report that it works great on LINE primitives.

Turns out the issue was something different. In the process of creating indices, I was also filtering the line through a simplification process. I hadn't been handling the index cleanup properly and that was resulting in weird accessors which caused the error in gltfpack.

Reading your weld code taught me a lot and I've managed to fix my process. Thanks for the awesome lib.