2 files changed, 161 insertions, 0 deletions
diff --git a/src/assets.rs b/src/assets.rs
new file mode 100644
index 0000000..58a6ed3
--- /dev/null
+++ b/src/assets.rs
@@ -0,0 +1,130 @@
+use std::{
+    io::{self, Cursor},
+    sync::Arc,
+};
+
+use async_channel::{Receiver, TryRecvError};
+use bevy::{
+    asset::{io::Reader, AssetLoader, AsyncReadExt, LoadContext},
+    audio::Source,
+    prelude::*,
+    tasks::AsyncComputeTaskPool,
+};
+use itertools::Itertools;
+use rustysynth::{MidiFile, MidiFileSequencer, SoundFont, Synthesizer, SynthesizerSettings};
+
+/// MIDI audio asset
+#[derive(Asset, TypePath)]
+pub struct MidiAudio {
+    /// MIDI file data
+    pub midi: Vec<u8>,
+}
+
+/// AssetLoader for MIDI files (.mid/.midi)
+#[derive(Default, Debug)]
+pub struct MidiAssetLoader;
+
+impl AssetLoader for MidiAssetLoader {
+    type Asset = MidiAudio;
+
+    type Settings = ();
+
+    type Error = io::Error;
+
+    async fn load<'a>(
+        &'a self,
+        reader: &'a mut Reader<'_>,
+        _settings: &'a Self::Settings,
+        _load_context: &'a mut LoadContext<'_>,
+    ) -> Result<Self::Asset, Self::Error> {
+        let mut bytes = vec![];
+        reader.read_to_end(&mut bytes).await?;
+        Ok(MidiAudio { midi: bytes })
+    }
+}
+
+/// Decoder for MIDI file playback
+pub struct MidiDecoder {
+    sample_rate: usize,
+    stream: Receiver<f32>,
+}
+
+impl MidiDecoder {
+    /// Construct and begin a new MIDI sequencer with the given MIDI data and soundfont.
+    ///
+    /// The sequencer will push at most 1 second's worth of audio ahead, allowing the decoder to
+    /// be paused without endlessly backing up data forever.
+    pub fn new(midi: Vec<u8>, soundfont: Arc<SoundFont>) -> Self {
+        let mut midi = Cursor::new(midi);
+        let sample_rate = 44100_usize;
+        let (tx, rx) = async_channel::bounded::<f32>(sample_rate * 2);
+        AsyncComputeTaskPool::get()
+            .spawn(async move {
+                let midi = Arc::new(MidiFile::new(&mut midi).expect("Failed to read midi file."));
+                let settings = SynthesizerSettings::new(sample_rate as i32);
+                let synthesizer =
+                    Synthesizer::new(&soundfont, &settings).expect("Failed to create synthesizer.");
+                let mut sequencer = MidiFileSequencer::new(synthesizer);
+                sequencer.play(&midi, true);
+
+                let mut left: Vec<f32> = vec![0_f32; sample_rate];
+                let mut right: Vec<f32> = vec![0_f32; sample_rate];
+                while !sequencer.end_of_sequence() {
+                    sequencer.render(&mut left, &mut right);
+                    for value in left.iter().interleave(right.iter()) {
+                        if let Err(e) = tx.send(*value).await {
+                            error!("{e}");
+                        };
+                    }
+                }
+                tx.close();
+            })
+            .detach();
+        Self {
+            sample_rate,
+            stream: rx,
+        }
+    }
+}
+
+impl Iterator for MidiDecoder {
+    type Item = f32;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        match self.stream.try_recv() {
+            Ok(value) => Some(value),
+            Err(e) => match e {
+                TryRecvError::Empty => Some(0.0),
+                TryRecvError::Closed => None,
+            },
+        }
+    }
+}
+
+impl Source for MidiDecoder {
+    fn current_frame_len(&self) -> Option<usize> {
+        None
+    }
+
+    fn channels(&self) -> u16 {
+        2
+    }
+
+    fn sample_rate(&self) -> u32 {
+        self.sample_rate as u32
+    }
+
+    fn total_duration(&self) -> Option<std::time::Duration> {
+        None
+    }
+}
+
+impl Decodable for MidiAudio {
+    type Decoder = MidiDecoder;
+
+    type DecoderItem = <MidiDecoder as Iterator>::Item;
+
+    fn decoder(&self) -> Self::Decoder {
+        MidiDecoder::new(self.midi.clone(), crate::SOUNDFONT.get().unwrap().clone())
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..2906d61
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,31 @@
+#![warn(missing_docs)]
+
+//! A plugin which adds MIDI file and soundfont audio support to the [bevy](https://crates.io/crates/bevy) engine via [rustysynth](https://crates.io/crates/rustysynth).
+
+use bevy::{audio::AddAudioSource, prelude::*};
+use rustysynth::SoundFont;
+use std::{
+    io::Read,
+    sync::{Arc, OnceLock},
+};
+
+mod assets;
+pub use assets::*;
+
+pub(crate) static SOUNDFONT: OnceLock<Arc<SoundFont>> = OnceLock::new();
+
+/// This plugin configures the soundfont used for playback and registers MIDI assets.
+#[derive(Default, Debug)]
+pub struct RustySynthPlugin<R: Read + Send + Sync + Clone + 'static> {
+    /// Reader for soundfont data. A default is not provided since soundfonts can be quite large.
+    pub soundfont: R,
+}
+
+impl<R: Read + Send + Sync + Clone + 'static> Plugin for RustySynthPlugin<R> {
+    fn build(&self, app: &mut App) {
+        let _ = SOUNDFONT.set(Arc::new(
+            SoundFont::new(&mut self.soundfont.clone()).unwrap(),
+        ));
+        app.add_audio_source::<MidiAudio>().init_asset::<MidiAudio>().init_asset_loader::<MidiAssetLoader>();
+    }
+}