bevy_common_assets 0.16.0

use bevy::prelude::*;
use bevy::reflect::TypePath;
use bevy_common_assets::json::JsonAssetPlugin;
use bevy_common_assets::ron::RonAssetPlugin;

fn main() {
    App::new()
        // You can add loaders for different asset types, but also multiple loaders for the same asset type
        // The important thing is: they all need distinct extensions!
        .add_plugins((
            DefaultPlugins,
            RonAssetPlugin::<Level>::new(&["level.ron"]),
            JsonAssetPlugin::<Level>::new(&["level.json"]),
        ))
        .init_state::<AppState>()
        .add_systems(Startup, setup)
        .add_systems(Update, check_loading.run_if(in_state(AppState::Loading)))
        .add_systems(OnEnter(AppState::Level), spawn_level)
        .run();
}

#[derive(serde::Deserialize, Asset, TypePath)]
struct Level {
    positions: Vec<[f32; 3]>,
}

fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
    let json_trees: Handle<Level> = asset_server.load("trees.level.json");
    let ron_trees: Handle<Level> = asset_server.load("trees.level.ron");
    commands.insert_resource(Levels(vec![json_trees, ron_trees]));
    let tree = ImageHandle(asset_server.load("tree.png"));
    commands.insert_resource(tree);

    commands.spawn((Camera2d, Msaa::Off));
}

fn spawn_level(
    mut commands: Commands,
    levels: Res<Levels>,
    tree: Res<ImageHandle>,
    mut level_assets: ResMut<Assets<Level>>,
) {
    for handle in levels.0.iter() {
        let level = level_assets.remove(handle).unwrap();
        for position in level.positions {
            commands.spawn((
                Sprite::from_image(tree.0.clone()),
                Transform::from_translation(position.into()),
            ));
        }
    }
}

fn check_loading(
    asset_server: Res<AssetServer>,
    handles: Res<Levels>,
    mut state: ResMut<NextState<AppState>>,
) {
    for handle in &handles.0 {
        if asset_server
            .get_load_state(handle)
            .map(|state| !state.is_loaded())
            .unwrap_or(true)
        {
            return;
        }
    }
    state.set(AppState::Level);
}

#[derive(Debug, Clone, Copy, Default, Eq, PartialEq, Hash, States)]
enum AppState {
    #[default]
    Loading,
    Level,
}

#[derive(Resource)]
struct ImageHandle(Handle<Image>);

#[derive(Resource)]
struct Levels(Vec<Handle<Level>>);