Add the ability to pass Vec<VecX> directly to mesh.set_attribute + simple example

[sarkahn]

Objective

With this pr we can pass Vec<VecX> directly to mesh.set_attribute. When working with custom meshes, particularly with procedural generation, I find it extremely helpful to work directly with Vec<VecX> to represent my mesh points/uvs/colors/etc.

Solution

Using bytemuck we can perform a conversion from Vec<VecX> to Vec<[f32;X]> when it gets passed to the mesh. Then we can use Vec<Vec3> directly to represent mesh points for example:

    let origin = Vec3::new(0.0, 0.0, 0.0);
    let right = Vec3::new(1.0, 0.0, 0.0);
    let up = Vec3::new(0.0, 1.0, 0.0);

    let positions = vec![
        origin + up,
        origin + up + right,
        origin,
        origin + right,
    ];

    let mut mesh = Mesh::new(PrimitiveTopology::TriangleList);
    mesh.set_attribute(Mesh::ATTRIBUTE_POSITION, positions);

[alice-i-cecile]

Could you retarget this to pipelined-rendering? That branch contains our rendering rework, and it would be much better to put the effort into improving the codebase there.

I suspect the basic idea should still hold, but you may have to do some reorganization and cleanup to match the new APIs.

[sarkahn]

Could you retarget this to pipelined-rendering? That branch contains our rendering rework, and it would be much better to put the effort into improving the codebase there.

I suspect the basic idea should still hold, but you may have to do some reorganization and cleanup to match the new APIs.

Done, looks like there were no issues.

[tim-blackbird]

This was superseded by #6442.