bevy/crates/bevy_asset
Niklas Eicker 77309ba5d8
Non-blocking load_untyped using a wrapper asset (#10198)
# Objective

- Assets v2 does not currently offer a public API to load untyped assets

## Solution

- Wrap the untyped handle in a `LoadedUntypedAsset` asset to offer a
non-blocking load for untyped assets. The user does not need to know the
actual asset type.
- Handles to `LoadedUntypedAsset` have the same path as the wrapped
asset, but their handles are shared using a label.

The user side of `load_untyped` looks like this:
```rust
use bevy::prelude::*;
use bevy_internal::asset::LoadedUntypedAsset;

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_systems(Startup, setup)
        .add_systems(Update, check)
        .run();
}

#[derive(Resource)]
struct UntypedAsset {
    handle: Handle<LoadedUntypedAsset>,
}

fn setup(
    mut commands: Commands,
    asset_server: Res<AssetServer>,
) {
    let handle = asset_server.load_untyped("branding/banner.png");
    commands.insert_resource(UntypedAsset { handle });
    commands.spawn(Camera2dBundle::default());
}

fn check(
    mut commands: Commands,
    res: Option<Res<UntypedAsset>>,
    assets: Res<Assets<LoadedUntypedAsset>>,
) {
    if let Some(untyped_asset) = res {
        if let Some(asset) = assets.get(&untyped_asset.handle) {
            commands.spawn(SpriteBundle {
                texture: asset.handle.clone().typed(),
                ..default()
            });
            commands.remove_resource::<UntypedAsset>();
        }
    }
}
```

---

## Changelog

- `load_untyped` on the asset server now returns a handle to a
`LoadedUntypedAsset` instead of an untyped handle to the asset at the
given path. The untyped handle for the given path can be retrieved from
the `LoadedUntypedAsset` once it is done loading.


## Migration Guide

Whenever possible use the typed API in order to directly get a handle to
your asset. If you do not know the type or need to use `load_untyped`
for a different reason, Bevy 0.12 introduces an additional layer of
indirection. The asset server will return a handle to a
`LoadedUntypedAsset`, which will load in the background. Once it is
loaded, the untyped handle to the asset file can be retrieved from the
`LoadedUntypedAsset`s field `handle`.

---------

Co-authored-by: Carter Anderson <mcanders1@gmail.com>
2023-10-26 22:14:32 +00:00
..
macros Fix unused variable warning for simple AssetV2 derives (#9961) 2023-09-29 08:08:13 +00:00
src Non-blocking load_untyped using a wrapper asset (#10198) 2023-10-26 22:14:32 +00:00
Cargo.toml few fmt tweaks (#10264) 2023-10-25 19:20:17 +00:00