bevy/examples/asset/custom_asset_reader.rs

//! Implements a custom asset io loader.
//! An [`AssetReader`] is what the asset server uses to read the raw bytes of assets.
//! It does not know anything about the asset formats, only how to talk to the underlying storage.

use bevy::{
    asset::io::{
        AssetReader, AssetReaderError, AssetSource, AssetSourceId, ErasedAssetReader, PathStream,
        Reader,
    },
    prelude::*,
};
use std::path::Path;

/// A custom asset reader implementation that wraps a given asset reader implementation
struct CustomAssetReader(Box<dyn ErasedAssetReader>);

impl AssetReader for CustomAssetReader {
    async fn read<'a>(&'a self, path: &'a Path) -> Result<impl Reader + 'a, AssetReaderError> {
        info!("Reading {:?}", path);
        self.0.read(path).await
    }
    async fn read_meta<'a>(&'a self, path: &'a Path) -> Result<impl Reader + 'a, AssetReaderError> {
        self.0.read_meta(path).await
    }

    async fn read_directory<'a>(
        &'a self,
        path: &'a Path,
    ) -> Result<Box<PathStream>, AssetReaderError> {
        self.0.read_directory(path).await
    }

    async fn is_directory<'a>(&'a self, path: &'a Path) -> Result<bool, AssetReaderError> {
        self.0.is_directory(path).await
    }
}

/// A plugins that registers our new asset reader
struct CustomAssetReaderPlugin;

impl Plugin for CustomAssetReaderPlugin {
    fn build(&self, app: &mut App) {
        app.register_asset_source(
            AssetSourceId::Default,
            AssetSource::build().with_reader(|| {
                Box::new(CustomAssetReader(
                    // This is the default reader for the current platform
                    AssetSource::get_default_reader("assets".to_string())(),
                ))
            }),
        );
    }
}

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

fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
    commands.spawn(Camera2dBundle::default());
    commands.spawn(SpriteBundle {
        texture: asset_server.load("branding/icon.png"),
        ..default()
    });
}