Using Sub-Assets

There are many elements of a glTF file including Scenes, Nodes, Meshes, Materials, Skins, Nodes, AnimationClips, etc. With appropriate care, these elements can be used to build up specific hierarchies for niche use cases.

Bevy's Gltf struct

Bevy's Gltf struct contains the processed glTF data, with and without names.

We'll be using named access because its clearer for written instructional content, which means we can use these fields on Gltf:

named_scenes: HashMap<Box<str>, Handle<Scene>>
named_meshes: HashMap<Box<str>, Handle<GltfMesh>>
named_materials: HashMap<Box<str>, Handle<StandardMaterial>>
named_nodes: HashMap<Box<str>, Handle<GltfNode>>
named_skins: HashMap<Box<str>, Handle<GltfSkin>>
named_animations: HashMap<Box<str>, Handle<AnimationClip>>

Spawning a Mesh (Custom Material)

Spawning a mesh from a glTF by itself seems straightforward at first, but Bevy's Mesh and GltfMesh are not the same concept. A Bevy Mesh is closer to a GltfPrimitive than a GltfMesh.

let handle = gltf.named_meshes.get("Sphere").unwrap();
let gltf_mesh = gltf_meshes.get(handle).unwrap();

commands.spawn((
    Mesh3d(gltf_mesh.primitives[0].mesh.clone()),
    MeshMaterial3d(materials.force_field.clone()),
    gltf_mesh.primitives[0]
        .extras
        .clone()
        .unwrap_or(GltfExtras::default()),
));

Using a Material

You can use materials in two ways: with or without the Bevy Components you applied in Blender.

Without Components

To apply a material from a glTF file you can access the handle via named_meshes by material name and use the handle directly. This approach is simpler but will not apply the Components you inserted in Blender.

let gltf = gltf.get(&gltf_handle).ok_or("couldn't get gltf")?;
let material_handle = gltf
    .named_materials
    .get("Wooden Panel")
    .ok_or("Couldn't get material handle")?;

commands.spawn((
    Mesh3d(meshes.add(Plane3d::new(
        Vec3::Y,
        Vec2::new(1.5, 1.5),
    ))),
    MeshMaterial3d(material_handle.clone()),
    Transform::from_xyz(0., 0., 0.)
));

With Components

If there are Components you applied in Blender that you want to also apply, you must gain access to the GltfExtras component and insert it alongside the material handle. If you followed the instructions in Exporting Materials to Files then you will have a simple mesh like a Sphere or Cube, which will have a single primitive associated with the material.

Everything here is set up to exist, but we'll use ok_or()? anyway because Bevy supports returning Result from systems.

let gltf = gltf.get(&gltf_handle).ok_or("couldn't get gltf")?;
let primitive = &gltf_meshes
    .get(
        gltf.named_meshes
            .get("WallBricksMesh")
            .ok_or("couldn't get gltf_mesh")?,
    )
    .ok_or("couldn't get gltf_primitive")?
    .primitives[0];

commands.spawn((
    Mesh3d(meshes.add(Plane3d::new(
        Vec3::Y,
        Vec2::new(1.5, 1.5),
    ))),
    MeshMaterial3d(
        primitive
            .material
            .clone()
            .ok_or("Option was None")?,
    ),
    Transform::from_xyz(0., 0., 0.),
    primitive
        .material_extras
        .clone()
        .ok_or("Option was None")?,
));