Audio control - play, pause, volume, speed, loop (#3948)

# Objective

- Add ways to control how audio is played

## Solution

- playing a sound will return a (weak) handle to an asset that can be used to control playback
- if the asset is dropped, it will detach the sink (same behaviour as now)

Cargo.toml

@@ -304,6 +304,10 @@ path = "examples/async_tasks/external_source_external_thread.rs"
 name = "audio"
 path = "examples/audio/audio.rs"
 
+[[example]]
+name = "audio_control"
+path = "examples/audio/audio_control.rs"
+
 # Diagnostics
 [[example]]
 name = "log_diagnostics"

crates/bevy_audio/src/audio.rs

@@ -1,5 +1,5 @@
-use crate::{AudioSource, Decodable};
-use bevy_asset::{Asset, Handle};
+use crate::{AudioSink, AudioSource, Decodable};
+use bevy_asset::{Asset, Handle, HandleId};
 use parking_lot::RwLock;
 use std::{collections::VecDeque, fmt};
 
@@ -18,7 +18,7 @@ where
     Source: Asset + Decodable,
 {
     /// Queue for playing audio from asset handles
-    pub queue: RwLock<VecDeque<Handle<Source>>>,
+    pub(crate) queue: RwLock<VecDeque<AudioToPlay<Source>>>,
 }
 
 impl<Source: Asset> fmt::Debug for Audio<Source>
@@ -55,7 +55,71 @@ where
     ///     audio.play(asset_server.load("my_sound.ogg"));
     /// }
     /// ```
-    pub fn play(&self, audio_source: Handle<Source>) {
-        self.queue.write().push_front(audio_source);
+    ///
+    /// Returns a weak [`Handle`] to the [`AudioSink`]. If this handle isn't changed to a
+    /// strong one, the sink will be detached and the sound will continue playing. Changing it
+    /// to a strong handle allows for control on the playback through the [`AudioSink`] asset.
+    ///
+    /// ```
+    /// # use bevy_ecs::system::Res;
+    /// # use bevy_asset::{AssetServer, Assets};
+    /// # use bevy_audio::{Audio, AudioSink};
+    /// fn play_audio_system(
+    ///     asset_server: Res<AssetServer>,
+    ///     audio: Res<Audio>,
+    ///     audio_sinks: Res<Assets<AudioSink>>,
+    /// ) {
+    ///     // This is a weak handle, and can't be used to control playback.
+    ///     let weak_handle = audio.play(asset_server.load("my_sound.ogg"));
+    ///     // This is now a strong handle, and can be used to control playback.
+    ///     let strong_handle = audio_sinks.get_handle(weak_handle);
+    /// }
+    /// ```
+    pub fn play(&self, audio_source: Handle<Source>) -> Handle<AudioSink> {
+        let id = HandleId::random::<AudioSink>();
+        let config = AudioToPlay {
+            repeat: false,
+            sink_handle: id,
+            source_handle: audio_source,
+        };
+        self.queue.write().push_back(config);
+        Handle::<AudioSink>::weak(id)
+    }
+
+    /// Play audio from a [`Handle`] to the audio source in a loop
+    ///
+    /// See [`Self::play`] on how to control playback.
+    pub fn play_in_loop(&self, audio_source: Handle<Source>) -> Handle<AudioSink> {
+        let id = HandleId::random::<AudioSink>();
+        let config = AudioToPlay {
+            repeat: true,
+            sink_handle: id,
+            source_handle: audio_source,
+        };
+        self.queue.write().push_back(config);
+        Handle::<AudioSink>::weak(id)
+    }
+}
+
+#[derive(Clone, PartialEq, Eq)]
+pub(crate) struct AudioToPlay<Source>
+where
+    Source: Asset + Decodable,
+{
+    pub(crate) sink_handle: HandleId,
+    pub(crate) source_handle: Handle<Source>,
+    pub(crate) repeat: bool,
+}
+
+impl<Source> fmt::Debug for AudioToPlay<Source>
+where
+    Source: Asset + Decodable,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("AudioToPlay")
+            .field("sink_handle", &self.sink_handle)
+            .field("source_handle", &self.source_handle)
+            .field("repeat", &self.repeat)
+            .finish()
     }
 }

crates/bevy_audio/src/audio_output.rs

@@ -1,8 +1,9 @@
 use crate::{Audio, AudioSource, Decodable};
 use bevy_asset::{Asset, Assets};
 use bevy_ecs::world::World;
+use bevy_reflect::TypeUuid;
 use bevy_utils::tracing::warn;
-use rodio::{OutputStream, OutputStreamHandle, Sink};
+use rodio::{OutputStream, OutputStreamHandle, Sink, Source};
 use std::marker::PhantomData;
 
 /// Used internally to play audio on the current "audio device"
@@ -41,25 +42,39 @@ impl<Source> AudioOutput<Source>
 where
     Source: Asset + Decodable,
 {
-    fn play_source(&self, audio_source: &Source) {
+    fn play_source(&self, audio_source: &Source, repeat: bool) -> Option<Sink> {
         if let Some(stream_handle) = &self.stream_handle {
             let sink = Sink::try_new(stream_handle).unwrap();
+            if repeat {
+                sink.append(audio_source.decoder().repeat_infinite());
+            } else {
                 sink.append(audio_source.decoder());
-            sink.detach();
+            }
+            Some(sink)
+        } else {
+            None
         }
     }
 
-    fn try_play_queued(&self, audio_sources: &Assets<Source>, audio: &mut Audio<Source>) {
+    fn try_play_queued(
+        &self,
+        audio_sources: &Assets<Source>,
+        audio: &mut Audio<Source>,
+        sinks: &mut Assets<AudioSink>,
+    ) {
         let mut queue = audio.queue.write();
         let len = queue.len();
         let mut i = 0;
         while i < len {
-            let audio_source_handle = queue.pop_back().unwrap();
-            if let Some(audio_source) = audio_sources.get(&audio_source_handle) {
-                self.play_source(audio_source);
+            let config = queue.pop_front().unwrap();
+            if let Some(audio_source) = audio_sources.get(&config.source_handle) {
+                if let Some(sink) = self.play_source(audio_source, config.repeat) {
+                    // don't keep the strong handle. there is no way to return it to the user here as it is async
+                    let _ = sinks.set(config.sink_handle, AudioSink { sink: Some(sink) });
+                }
             } else {
                 // audio source hasn't loaded yet. add it back to the queue
-                queue.push_front(audio_source_handle);
+                queue.push_back(config);
             }
             i += 1;
         }
@@ -74,8 +89,101 @@ where
     let world = world.cell();
     let audio_output = world.get_non_send::<AudioOutput<Source>>().unwrap();
     let mut audio = world.get_resource_mut::<Audio<Source>>().unwrap();
+    let mut sinks = world.get_resource_mut::<Assets<AudioSink>>().unwrap();
 
     if let Some(audio_sources) = world.get_resource::<Assets<Source>>() {
-        audio_output.try_play_queued(&*audio_sources, &mut *audio);
+        audio_output.try_play_queued(&*audio_sources, &mut *audio, &mut *sinks);
     };
 }
+
+/// Asset controlling the playback of a sound
+///
+/// ```
+/// # use bevy_ecs::system::{Local, Res};
+/// # use bevy_asset::{Assets, Handle};
+/// # use bevy_audio::AudioSink;
+/// // Execution of this system should be controlled by a state or input,
+/// // otherwise it would just toggle between play and pause every frame.
+/// fn pause(
+///     audio_sinks: Res<Assets<AudioSink>>,
+///     music_controller: Local<Handle<AudioSink>>,
+/// ) {
+///     if let Some(sink) = audio_sinks.get(&*music_controller) {
+///         if sink.is_paused() {
+///             sink.play()
+///         } else {
+///             sink.pause()
+///         }
+///     }
+/// }
+/// ```
+///
+#[derive(TypeUuid)]
+#[uuid = "8BEE570C-57C2-4FC0-8CFB-983A22F7D981"]
+pub struct AudioSink {
+    // This field is an Option in order to allow us to have a safe drop that will detach the sink.
+    // It will never be None during its life
+    sink: Option<Sink>,
+}
+
+impl Drop for AudioSink {
+    fn drop(&mut self) {
+        self.sink.take().unwrap().detach();
+    }
+}
+
+impl AudioSink {
+    /// Gets the volume of the sound.
+    ///
+    /// The value `1.0` is the "normal" volume (unfiltered input). Any value other than `1.0`
+    /// will multiply each sample by this value.
+    pub fn volume(&self) -> f32 {
+        self.sink.as_ref().unwrap().volume()
+    }
+
+    /// Changes the volume of the sound.
+    ///
+    /// The value `1.0` is the "normal" volume (unfiltered input). Any value other than `1.0`
+    /// will multiply each sample by this value.
+    pub fn set_volume(&self, volume: f32) {
+        self.sink.as_ref().unwrap().set_volume(volume);
+    }
+
+    /// Gets the speed of the sound.
+    ///
+    /// The value `1.0` is the "normal" speed (unfiltered input). Any value other than `1.0`
+    /// will change the play speed of the sound.
+    pub fn speed(&self) -> f32 {
+        self.sink.as_ref().unwrap().speed()
+    }
+
+    /// Changes the speed of the sound.
+    ///
+    /// The value `1.0` is the "normal" speed (unfiltered input). Any value other than `1.0`
+    /// will change the play speed of the sound.
+    pub fn set_speed(&self, speed: f32) {
+        self.sink.as_ref().unwrap().set_speed(speed);
+    }
+
+    /// Resumes playback of a paused sink.
+    ///
+    /// No effect if not paused.
+    pub fn play(&self) {
+        self.sink.as_ref().unwrap().play();
+    }
+
+    /// Pauses playback of this sink.
+    ///
+    /// No effect if already paused.
+    /// A paused sink can be resumed with [`play`](Self::play).
+    pub fn pause(&self) {
+        self.sink.as_ref().unwrap().pause();
+    }
+
+    /// Is this sink paused?
+    ///
+    /// Sinks can be paused and resumed using [`pause`](Self::pause) and [`play`](Self::play).
+    pub fn is_paused(&self) -> bool {
+        self.sink.as_ref().unwrap().is_paused()
+    }
+}

crates/bevy_audio/src/lib.rs

@@ -56,6 +56,7 @@ impl Plugin for AudioPlugin {
     fn build(&self, app: &mut App) {
         app.init_non_send_resource::<AudioOutput<AudioSource>>()
             .add_asset::<AudioSource>()
+            .add_asset::<AudioSink>()
             .init_resource::<Audio<AudioSource>>()
             .add_system_to_stage(
                 CoreStage::PostUpdate,

examples/README.md

@@ -153,6 +153,7 @@ Example | File | Description
 Example | File | Description
 --- | --- | ---
 `audio` | [`audio/audio.rs`](./audio/audio.rs) | Shows how to load and play an audio file
+`audio_control` | [`audio/audio_control.rs`](./audio/audio_control.rs) | Shows how to load and play an audio file, and control how it's played
 
 ## Diagnostics
 

examples/audio/audio_control.rs

@@ -0,0 +1,65 @@
+use bevy::{audio::AudioSink, prelude::*};
+
+/// This example illustrates how to load and play an audio file, and control how it's played
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_startup_system(setup)
+        .add_system(update_speed)
+        .add_system(pause)
+        .add_system(volume)
+        .run();
+}
+
+fn setup(
+    mut commands: Commands,
+    asset_server: Res<AssetServer>,
+    audio: Res<Audio>,
+    audio_sinks: Res<Assets<AudioSink>>,
+) {
+    let music = asset_server.load("sounds/Windless Slopes.ogg");
+    let handle = audio_sinks.get_handle(audio.play(music));
+    commands.insert_resource(MusicController(handle));
+}
+
+struct MusicController(Handle<AudioSink>);
+
+fn update_speed(
+    audio_sinks: Res<Assets<AudioSink>>,
+    music_controller: Res<MusicController>,
+    time: Res<Time>,
+) {
+    if let Some(sink) = audio_sinks.get(&music_controller.0) {
+        sink.set_speed(((time.seconds_since_startup() / 5.0).sin() as f32 + 1.0).max(0.1));
+    }
+}
+
+fn pause(
+    keyboard_input: Res<Input<KeyCode>>,
+    audio_sinks: Res<Assets<AudioSink>>,
+    music_controller: Res<MusicController>,
+) {
+    if keyboard_input.just_pressed(KeyCode::Space) {
+        if let Some(sink) = audio_sinks.get(&music_controller.0) {
+            if sink.is_paused() {
+                sink.play()
+            } else {
+                sink.pause()
+            }
+        }
+    }
+}
+
+fn volume(
+    keyboard_input: Res<Input<KeyCode>>,
+    audio_sinks: Res<Assets<AudioSink>>,
+    music_controller: Res<MusicController>,
+) {
+    if let Some(sink) = audio_sinks.get(&music_controller.0) {
+        if keyboard_input.just_pressed(KeyCode::Plus) {
+            sink.set_volume(sink.volume() + 0.1);
+        } else if keyboard_input.just_pressed(KeyCode::Minus) {
+            sink.set_volume(sink.volume() - 0.1);
+        }
+    }
+}