Complete inline documentation for bevy_audio (#3510)

# Objective
Part of #3492 

- Complete inline documentation of `bevy_audio`

## Solution

- Added inline documentation to all public parts of `bevy_audio`
- Added a few inline examples at important places
- Some renaming for clarity (e.g. `AudioLoader` and generics)
- added `#![warn(missing_docs)]` and `#![forbid(unsafe_code)]` to `bevy_audio`

I also tried adding support for the other vorbis file endings `.oga` and `.spx` to the `AudioLoader` (see `file endings` at https://tools.ietf.org/html/rfc5334#section-10.3), but the `rodio` decoder does not seem to support those.

crates/bevy_audio/Cargo.toml

@@ -24,6 +24,10 @@ parking_lot = "0.11.0"
 [target.'cfg(target_arch = "wasm32")'.dependencies]
 rodio = { version = "0.14", default-features = false, features = ["wasm-bindgen"] }
 
+[dev-dependencies]
+# bevy
+bevy_internal = { path = "../bevy_internal", version = "0.5.0" }
+
 [features]
 mp3 = ["rodio/mp3"]
 flac = ["rodio/flac"]

crates/bevy_audio/src/audio.rs

@@ -3,26 +3,36 @@ use bevy_asset::{Asset, Handle};
 use parking_lot::RwLock;
 use std::{collections::VecDeque, fmt};
 
-/// The external struct used to play audio
-pub struct Audio<P = AudioSource>
+/// Use this resource to play audio
+///
+/// ```
+/// # use bevy_ecs::system::Res;
+/// # use bevy_asset::AssetServer;
+/// # use bevy_audio::Audio;
+/// fn play_audio_system(asset_server: Res<AssetServer>, audio: Res<Audio>) {
+///     audio.play(asset_server.load("my_sound.ogg"));
+/// }
+/// ```
+pub struct Audio<Source = AudioSource>
 where
-    P: Asset + Decodable,
+    Source: Asset + Decodable,
 {
-    pub queue: RwLock<VecDeque<Handle<P>>>,
+    /// Queue for playing audio from asset handles
+    pub queue: RwLock<VecDeque<Handle<Source>>>,
 }
 
-impl<P: Asset> fmt::Debug for Audio<P>
+impl<Source: Asset> fmt::Debug for Audio<Source>
 where
-    P: Decodable,
+    Source: Decodable,
 {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.debug_struct("Audio").field("queue", &self.queue).finish()
     }
 }
 
-impl<P> Default for Audio<P>
+impl<Source> Default for Audio<Source>
 where
-    P: Asset + Decodable,
+    Source: Asset + Decodable,
 {
     fn default() -> Self {
         Self {
@@ -31,13 +41,21 @@ where
     }
 }
 
-impl<P> Audio<P>
+impl<Source> Audio<Source>
 where
-    P: Asset + Decodable,
-    <P as Decodable>::Decoder: rodio::Source + Send + Sync,
-    <<P as Decodable>::Decoder as Iterator>::Item: rodio::Sample + Send + Sync,
+    Source: Asset + Decodable,
 {
-    pub fn play(&self, audio_source: Handle<P>) {
+    /// Play audio from a [`Handle`] to the audio source
+    ///
+    /// ```
+    /// # use bevy_ecs::system::Res;
+    /// # use bevy_asset::AssetServer;
+    /// # use bevy_audio::Audio;
+    /// fn play_audio_system(asset_server: Res<AssetServer>, audio: Res<Audio>) {
+    ///     audio.play(asset_server.load("my_sound.ogg"));
+    /// }
+    /// ```
+    pub fn play(&self, audio_source: Handle<Source>) {
         self.queue.write().push_front(audio_source);
     }
 }

crates/bevy_audio/src/audio_output.rs

@@ -6,18 +6,18 @@ use rodio::{OutputStream, OutputStreamHandle, Sink};
 use std::marker::PhantomData;
 
 /// Used internally to play audio on the current "audio device"
-pub struct AudioOutput<P = AudioSource>
+pub struct AudioOutput<Source = AudioSource>
 where
-    P: Decodable,
+    Source: Decodable,
 {
     _stream: Option<OutputStream>,
     stream_handle: Option<OutputStreamHandle>,
-    phantom: PhantomData<P>,
+    phantom: PhantomData<Source>,
 }
 
-impl<P> Default for AudioOutput<P>
+impl<Source> Default for AudioOutput<Source>
 where
-    P: Decodable,
+    Source: Decodable,
 {
     fn default() -> Self {
         if let Ok((stream, stream_handle)) = OutputStream::try_default() {
@@ -37,13 +37,11 @@ where
     }
 }
 
-impl<P> AudioOutput<P>
+impl<Source> AudioOutput<Source>
 where
-    P: Asset + Decodable,
-    <P as Decodable>::Decoder: rodio::Source + Send + Sync,
-    <<P as Decodable>::Decoder as Iterator>::Item: rodio::Sample + Send + Sync,
+    Source: Asset + Decodable,
 {
-    fn play_source(&self, audio_source: &P) {
+    fn play_source(&self, audio_source: &Source) {
         if let Some(stream_handle) = &self.stream_handle {
             let sink = Sink::try_new(stream_handle).unwrap();
             sink.append(audio_source.decoder());
@@ -51,7 +49,7 @@ where
         }
     }
 
-    fn try_play_queued(&self, audio_sources: &Assets<P>, audio: &mut Audio<P>) {
+    fn try_play_queued(&self, audio_sources: &Assets<Source>, audio: &mut Audio<Source>) {
         let mut queue = audio.queue.write();
         let len = queue.len();
         let mut i = 0;
@@ -69,17 +67,15 @@ where
 }
 
 /// Plays audio currently queued in the [`Audio`] resource through the [`AudioOutput`] resource
-pub fn play_queued_audio_system<P: Asset>(world: &mut World)
+pub fn play_queued_audio_system<Source: Asset>(world: &mut World)
 where
-    P: Decodable,
-    <P as Decodable>::Decoder: rodio::Source + Send + Sync,
-    <<P as Decodable>::Decoder as Iterator>::Item: rodio::Sample + Send + Sync,
+    Source: Decodable,
 {
     let world = world.cell();
-    let audio_output = world.get_non_send::<AudioOutput<P>>().unwrap();
-    let mut audio = world.get_resource_mut::<Audio<P>>().unwrap();
+    let audio_output = world.get_non_send::<AudioOutput<Source>>().unwrap();
+    let mut audio = world.get_resource_mut::<Audio<Source>>().unwrap();
 
-    if let Some(audio_sources) = world.get_resource::<Assets<P>>() {
+    if let Some(audio_sources) = world.get_resource::<Assets<Source>>() {
         audio_output.try_play_queued(&*audio_sources, &mut *audio);
     };
 }

crates/bevy_audio/src/audio_source.rs

@@ -8,6 +8,7 @@ use std::{io::Cursor, sync::Arc};
 #[derive(Debug, Clone, TypeUuid)]
 #[uuid = "7a14806a-672b-443b-8d16-4f18afefa463"]
 pub struct AudioSource {
+    /// Raw data of the audio source
     pub bytes: Arc<[u8]>,
 }
 
@@ -17,11 +18,18 @@ impl AsRef<[u8]> for AudioSource {
     }
 }
 
-/// Loads mp3 files as [`AudioSource`] [`Assets`](bevy_asset::Assets)
+/// Loads files as [`AudioSource`] [`Assets`](bevy_asset::Assets)
+///
+/// This asset loader supports different audio formats based on the enable Bevy features.
+/// The feature `bevy/vorbis` enables loading from `.ogg` files and is enabled by default.
+/// Other file endings can be loaded from with additional features:
+/// `.mp3` with `bevy/mp3`
+/// `.flac` with `bevy/flac`
+/// `.wav` with `bevy/wav`
 #[derive(Default)]
-pub struct Mp3Loader;
+pub struct AudioLoader;
 
-impl AssetLoader for Mp3Loader {
+impl AssetLoader for AudioLoader {
     fn load(&self, bytes: &[u8], load_context: &mut LoadContext) -> BoxedFuture<Result<()>> {
         load_context.set_default_asset(LoadedAsset::new(AudioSource {
             bytes: bytes.into(),
@@ -43,14 +51,20 @@ impl AssetLoader for Mp3Loader {
     }
 }
 
+/// A type implementing this trait can be decoded as a rodio source
 pub trait Decodable: Send + Sync + 'static {
-    type Decoder;
+    /// The decoder that can decode the implemeting type
+    type Decoder: rodio::Source + Send + Sync + Iterator<Item = Self::DecoderItem>;
+    /// A single value given by the decoder
+    type DecoderItem: rodio::Sample + Send + Sync;
 
+    /// Build and return a [`Self::Decoder`] for the implementing type
     fn decoder(&self) -> Self::Decoder;
 }
 
 impl Decodable for AudioSource {
     type Decoder = rodio::Decoder<Cursor<AudioSource>>;
+    type DecoderItem = <rodio::Decoder<Cursor<AudioSource>> as Iterator>::Item;
 
     fn decoder(&self) -> Self::Decoder {
         rodio::Decoder::new(Cursor::new(self.clone())).unwrap()

crates/bevy_audio/src/lib.rs

@@ -1,7 +1,38 @@
+//! Audio support for the game engine Bevy
+//!
+//! ```
+//! # use bevy_ecs::{system::Res, event::EventWriter};
+//! # use bevy_audio::{Audio, AudioPlugin};
+//! # use bevy_asset::{AssetPlugin, AssetServer};
+//! # use bevy_app::{App, AppExit};
+//! # use bevy_internal::MinimalPlugins;
+//! fn main() {
+//!    App::new()
+//!         .add_plugins(MinimalPlugins)
+//!         .add_plugin(AssetPlugin)
+//!         .add_plugin(AudioPlugin)
+//! #       .add_system(stop)
+//!         .add_startup_system(play_background_audio)
+//!         .run();
+//! }
+//!
+//! fn play_background_audio(asset_server: Res<AssetServer>, audio: Res<Audio>) {
+//!     audio.play(asset_server.load("background_audio.ogg"));
+//! }
+//!
+//! # fn stop(mut events: EventWriter<AppExit>) {
+//! #     events.send(AppExit)
+//! # }
+//! ```
+
+#![forbid(unsafe_code)]
+#![warn(missing_docs)]
+
 mod audio;
 mod audio_output;
 mod audio_source;
 
+#[allow(missing_docs)]
 pub mod prelude {
     #[doc(hidden)]
     pub use crate::{Audio, AudioOutput, AudioSource, Decodable};
@@ -15,7 +46,9 @@ use bevy_app::prelude::*;
 use bevy_asset::AddAsset;
 use bevy_ecs::system::IntoExclusiveSystem;
 
-/// Adds support for audio playback to an App
+/// Adds support for audio playback to a Bevy Application
+///
+/// Use the [`Audio`] resource to play audio.
 #[derive(Default)]
 pub struct AudioPlugin;
 
@@ -30,6 +63,6 @@ impl Plugin for AudioPlugin {
             );
 
         #[cfg(any(feature = "mp3", feature = "flac", feature = "wav", feature = "vorbis"))]
-        app.init_asset_loader::<Mp3Loader>();
+        app.init_asset_loader::<AudioLoader>();
     }
 }