feat: modularize sin wave generator

raust-cli/src/main.rs

@@ -1,6 +1,6 @@
 use clap::Parser;
 use cpal::traits::DeviceTrait;
-use raust_engine::{AudioPlayer, Note};
+use raust_engine::{AudioPlayer, Note, generators::Generator};
 
 /// Play a single tone through the default audio output device.
 #[derive(Parser, Debug)]
@@ -24,16 +24,8 @@ fn main() -> anyhow::Result<()> {
     let (device, config) = raust_engine::get_device_and_config()?;
     println!("Output device: {}", device.id()?);
     println!("Default output config: {config:?}");
-    let mut clock = 0f32;
-    // Sample rates are a few hundred kHz at most, nowhere near f32's
-    // 24-bit exact-integer range, so this cast never loses precision.
-    #[allow(clippy::cast_precision_loss, clippy::as_conversions)]
-    let sample_rate = config.sample_rate() as f32;
-    let generator = move || {
-        clock = (clock + 1.0) % sample_rate;
-        (clock * note.pitch * 2.0 * std::f32::consts::PI / sample_rate).sin()
-    };
-    let audio_player = AudioPlayer::try_new(&device, config, Box::new(generator))?;
+    let mut sin = raust_engine::generators::SinWave::new(config.sample_rate(), note.pitch);
+    let audio_player = AudioPlayer::try_new(&device, config, Box::new(move || sin.generate()))?;
 
     audio_player.play()?;
     std::thread::sleep(std::time::Duration::from_millis(note.length));

raust-engine/src/audio_player.rs

@@ -8,7 +8,7 @@
 pub struct AudioPlayer {
     stream: Stream,
 }
-use super::Generator;
+use crate::generators::GeneratorFn;
 use cpal::{
     Device, Error, ErrorKind, FromSample, I24, OutputCallbackInfo, Sample, SampleFormat, SizedSample, Stream, StreamConfig, SupportedStreamConfig, traits::{DeviceTrait, StreamTrait},
 };
@@ -27,7 +27,7 @@ impl AudioPlayer {
     /// Returns an error if:
     /// - the device reports a sample format `raust` does not support, or
     /// - CPAL fails to build the output stream.
-    pub fn try_new(device: &Device, config: SupportedStreamConfig, generator: Generator) -> anyhow::Result<Self> {
+    pub fn try_new(device: &Device, config: SupportedStreamConfig, generator: GeneratorFn) -> anyhow::Result<Self> {
         let stream = match config.sample_format() {
             SampleFormat::I8 => Self::create_stream::<i8>(device, config.into(), generator),
             SampleFormat::I16 => Self::create_stream::<i16>(device, config.into(), generator),
@@ -57,7 +57,7 @@ impl AudioPlayer {
     pub fn create_stream<T>(
         device: &Device,
         config: StreamConfig,
-        mut generator: Generator,
+        mut generator: GeneratorFn,
     ) -> Result<Stream, anyhow::Error>
     where
         T: SizedSample + FromSample<f32>,

raust-engine/src/generators/mod.rs

@@ -0,0 +1,14 @@
+mod sin_wave;
+pub use sin_wave::SinWave;
+
+pub trait Generator {
+    fn generate(&mut self) -> f32;
+}
+
+/// Produces one `f32` sample per call.
+///
+/// `AudioPlayer` consumes a `Generator` when it builds its stream and moves
+/// it onto the audio callback thread, so `Send + 'static` must hold — the
+/// same bound [`cpal::Device::build_output_stream`] places on its data
+/// callback.
+pub type GeneratorFn = Box<dyn FnMut() -> f32 + Send + 'static>;

raust-engine/src/generators/sin_wave.rs

@@ -0,0 +1,30 @@
+use cpal::SampleRate;
+
+use crate::{Phase, Pitch};
+
+use super::Generator;
+
+pub struct SinWave {
+    phase: Phase,
+    pitch: Pitch,
+    sample_rate: f32
+}
+
+impl SinWave {
+    #[must_use]
+    pub fn new(sample_rate: SampleRate, pitch: Pitch) -> Self {
+        #[allow(clippy::cast_precision_loss, clippy::as_conversions)]
+        let sample_rate = sample_rate as f32;
+        Self {
+            phase: Phase::new(sample_rate, None),
+            pitch,
+            sample_rate
+        }
+    }
+}
+
+impl Generator for SinWave {
+    fn generate(&mut self) -> f32 {
+        (self.phase.next() * self.pitch * 2.0 * std::f32::consts::PI / self.sample_rate).sin()
+    }
+}

raust-engine/src/lib.rs

@@ -5,14 +5,11 @@ mod audio_player;
 pub use audio_player::AudioPlayer;
 mod init;
 pub use init::*;
+pub mod generators;
+mod phase;
+pub(crate) use phase::Phase;
 
-/// Produces one `f32` sample per call.
-///
-/// `AudioPlayer` consumes a `Generator` when it builds its stream and moves
-/// it onto the audio callback thread, so `Send + 'static` must hold — the
-/// same bound [`cpal::Device::build_output_stream`] places on its data
-/// callback.
-pub type Generator = Box<dyn FnMut() -> f32 + Send + 'static>;
+type Pitch = f32;
 
 /// A single tone: a pitch held for a fixed duration.
 #[derive(Debug, Clone, Copy)]

raust-engine/src/phase.rs

@@ -0,0 +1,24 @@
+type PhaseFn = Box<dyn FnMut(f32, f32) -> f32 + Send + 'static>; // (current, sample_rate) -> next
+
+pub struct Phase {
+    current: f32,
+    sample_rate: f32,
+    next_fn: PhaseFn
+}
+
+impl Phase {
+    pub fn new(sample_rate: f32, next_fn: Option<PhaseFn>) -> Self {
+        Self {
+            current: 0.0,
+            sample_rate,
+            next_fn: next_fn.unwrap_or_else(|| {
+                Box::new(|current: f32, sample_rate: f32| (current + 1.0) % sample_rate)
+            })
+        }
+    }
+
+    pub fn next(&mut self) -> f32 {
+        self.current = (self.next_fn)(self.current, self.sample_rate);
+        self.current
+    }
+}