GLTF extension support

[CorneliusCornbread]

Objective

Adds support for accessing raw extension data of loaded GLTF assets

Solution

Via the GLTF loader settings, you can specify whether or not to include the GLTF source. While not the ideal way of solving this problem, modeling all of GLTF within Bevy just for extensions adds a lot of complexity to the way Bevy handles GLTF currently. See the example GLTF meta file and code

(
    meta_format_version: "1.0",
    asset: Load(
        loader: "bevy_gltf::loader::GltfLoader",
        settings: (
            load_meshes: true,
            load_cameras: true,
            load_lights: true,
            include_source: true,
        ),
    ),
)

pub fn load_gltf(mut commands: Commands, assets: Res<AssetServer>) {
    let my_gltf = assets.load("test_platform.gltf");

    commands.insert_resource(MyAssetPack {
        spawned: false,
        handle: my_gltf,
    });
}

#[derive(Resource)]
pub struct MyAssetPack {
    pub spawned: bool,
    pub handle: Handle<Gltf>,
}

pub fn spawn_gltf_objects(
    mut commands: Commands,
    mut my: ResMut<MyAssetPack>,
    assets_gltf: Res<Assets<Gltf>>,
) {
    // This flag is used to because this system has to be run until the asset is loaded.
    // If there's a better way of going about this I am unaware of it.
    if my.spawned {
        return;
    }

    if let Some(gltf) = assets_gltf.get(&my.handle) {
        info!("spawn");
        my.spawned = true;
        // spawn the first scene in the file
        commands.spawn(SceneBundle {
            scene: gltf.scenes[0].clone(),
            ..Default::default()
        });

        let source = gltf.source.as_ref().unwrap();
        info!("materials count {}", &source.materials().size_hint().0);
        info!(
            "materials ext is some {}",
            &source.materials().next().unwrap().extensions().is_some()
        );
    }
}

---

Changelog

Added support for GLTF extensions through including raw GLTF source via loader flag GltfLoaderSettings::include_source == true, stored in Gltf::source: Option<gltf::Gltf>

Migration Guide

This will have issues with "asset migrations", as there is currently no way for .meta files to be migrated. Attempting to migrate .meta files without the new flag will yield the following error:

bevy_asset::server: Failed to deserialize meta for asset test_platform.gltf: Failed to deserialize asset meta: SpannedError { code: MissingStructField { field: "include_source", outer: Some("GltfLoaderSettings") }, position: Position { line: 9, col: 9 } }

This means users who want to migrate their .meta files will have to add the include_source: true, setting to their meta files by hand.

[github-actions]

Welcome, new contributor!

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[kaosat-dev]

Hi @CorneliusCornbread !
Thanks for the pull request !
Just wanted to let you know I started looking at your changes & proposal, will do a full review this week.

[kaosat-dev]

Simple & clear, works fine locally I think it is all good ! Thanks a lot for your PR ! :)
Some minor thoughts:

• I do not really think the meta migration is much of an issue, but that could be just me
• I usually favour having a small example for new features, but I seem to recall the Bevy team likes to keep the examples minimal to prevent too much bloat, but perhaps @alice-i-cecile has some input on that ?

[kaosat-dev]

good call ! v 1.4.0 has some nice improvements

[CorneliusCornbread]

This is also a requirement for the extensions, 1.4.0 adds the extensions feature flag. There's also some fixes for large gltf's with large buffers which is nice

[kaosat-dev]

I think this is ok.
I wondered if it would be better hidden behind a feature flag like named_animations but it would not really make sense at the bevy level imho.

[CorneliusCornbread]

Yeah, I think this makes sense, the idea is that if you don't need the extra data for some assets you can save on memory for those models specifically. Sometimes we only need the model data we're extracting normally.

[kaosat-dev]

Just an additional 2 cents regarding your comment in your example code:

// This flag is used to because this system has to be run until the asset is loaded.
// If there's a better way of going about this I am unaware of it.
if my.spawned {
    return;
}

you can use asset_server.get_load_state(handle) to get the LoadState of an asset and match on that :)