bevy/examples/audio/spatial_audio_2d.rs

//! This example illustrates how to load and play an audio file, and control where the sounds seems to come from.
use bevy::{prelude::*, sprite::MaterialMesh2dBundle};

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

/// Spatial audio uses the distance to attenuate the sound volume. In 2D with the default camera, 1 pixel is 1 unit of distance,
/// so we use a scale so that 100 pixels is 1 unit of distance for audio.
const AUDIO_SCALE: f32 = 100.0;

fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<ColorMaterial>>,
    asset_server: Res<AssetServer>,
) {
    // Space between the two ears
    let gap = 400.0;

    // sound emitter
    commands.spawn((
        MaterialMesh2dBundle {
            mesh: meshes.add(shape::Circle::new(15.0).into()).into(),
            material: materials.add(ColorMaterial::from(Color::BLUE)),
            transform: Transform::from_translation(Vec3::new(0.0, 50.0, 0.0)),
            ..default()
        },
        Emitter,
        SpatialAudioBundle {
            source: asset_server.load("sounds/Windless Slopes.ogg"),
            settings: PlaybackSettings::LOOP,
            spatial: SpatialSettings::new(Transform::IDENTITY, gap / AUDIO_SCALE, Vec3::ZERO),
        },
    ));

    // left ear
    commands.spawn(SpriteBundle {
        sprite: Sprite {
            color: Color::RED,
            custom_size: Some(Vec2::splat(20.0)),
            ..default()
        },
        transform: Transform::from_xyz(-gap / 2.0, 0.0, 0.0),
        ..default()
    });

    // right ear
    commands.spawn(SpriteBundle {
        sprite: Sprite {
            color: Color::GREEN,
            custom_size: Some(Vec2::splat(20.0)),
            ..default()
        },
        transform: Transform::from_xyz(gap / 2.0, 0.0, 0.0),
        ..default()
    });

    // camera
    commands.spawn(Camera2dBundle::default());
}

#[derive(Component)]
struct Emitter;

fn update_positions(
    time: Res<Time>,
    mut emitters: Query<(&mut Transform, Option<&SpatialAudioSink>), With<Emitter>>,
) {
    for (mut emitter_transform, sink) in emitters.iter_mut() {
        emitter_transform.translation.x = time.elapsed_seconds().sin() * 500.0;
        if let Some(sink) = &sink {
            sink.set_emitter_position(emitter_transform.translation / AUDIO_SCALE);
        }
    }
}