Code Review Request: struggling to export mesh as a gltf.

[charred remnant]

I have a mesh generated in bevy which i'd like to convert into a GLTF, but I'm running into issues with adding support for the mesh's indices to it.

The gltf generates, but when i test importing it into blender I get index out of bounds errors from blender, telling me that this file is malformed.

Anyone familiar with gltf files able to point to what I could be doing wrong?

error:

[urban knot]

that error looks like it is a generic multidimensional-array indexing error, not referring to indices in the mesh sense

so the problem could be things that are not mesh indices

though this sounds plausibly that data which is not a proper index is being interpreted as an index

since a cube mesh has 24 vertices

oh, your fn to_padded_byte_vector<T>(vec: Vec<T>) -> Vec<u8> is unsound. this probably isn't the actual bug, but if you want to reinterpret data like this, you should use bytemuck or zerocopy, instead of writing your own unsafe code

[charred remnant]

I don't know what it does, or why its there. I copied it from this example from the gltf crate example page:
https://github.com/gltf-rs/gltf/blob/main/examples/export/main.rs

It looks like you made a commit to this example though. what does turning it into a padded byte vector do?

[urban knot]

my commit was completely unrelated to that part 😅

the point of that function is to turn a vector of numbers into a vector of the bytes that represent those numbers

but it is doing it very badly. probably in a way which won't corrupt your data, but still, incorrect

[charred remnant]

you said bytemuck/zerocopy can do it?

[urban knot]

yes, bytemuck::bytes_of() is a safe, sound function that can be used as the main part of a correct solution

[charred remnant]

someone in a dfferent recommended this:

// bytemuck crate uses unsafe under the hood.
fn dynamic_mesh_to_bytes(mesh: &Mesh) -> Vec<u8> {
    let mut bytes = Vec::new();
    bytes.extend_from_slice(bytemuck::cast_slice(&mesh.vertices));
    bytes.extend_from_slice(bytemuck::cast_slice(&mesh.indices));
    bytes
}

[urban knot]

yeah that's good

well, it doesn't pad anything but you may or may not need padding

[charred remnant]

I have been getting a problem with the buffer being too small recently though on import. Will not having the padding lead to that issue?

[charred remnant]

Does anyone have a codebase that serializes a mesh to gltf? I'm drawing blanks on how to solve these errors and nothing comes to mind as immediately wrong.