From 4e48fbed2114b8b47b4ed8d62750c29617fb2b6d Mon Sep 17 00:00:00 2001
From: Jeron Aldaron Lau <aldaronlau@gmail.com>
Date: Wed, 16 Feb 2022 20:12:01 -0600
Subject: [PATCH] Add audio mixing example.

---
 Cargo.toml      |   2 +-
 examples/mix.rs | 117 ++++++++++++++++++++++++++++++++++++++++++++++++
 src/math.rs     |   2 +-
 3 files changed, 119 insertions(+), 2 deletions(-)
 create mode 100644 examples/mix.rs

diff --git a/Cargo.toml b/Cargo.toml
index cf40392..a63b815 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -33,7 +33,7 @@ categories = [
     "data-structures",
     "no-std",
 ]
-include = ["Cargo.toml", "src/*"]
+include = ["README.md", "Cargo.toml", "src/*"]
 
 [dependencies]
 libm = "0.2"
diff --git a/examples/mix.rs b/examples/mix.rs
new file mode 100644
index 0000000..234f9a8
--- /dev/null
+++ b/examples/mix.rs
@@ -0,0 +1,117 @@
+// Audio mixing example
+
+use fon::{
+    chan::{Ch32, Channel},
+    Audio, Frame, Sink, Stream,
+};
+use std::num::NonZeroU32;
+
+#[derive(Debug)]
+pub struct Mixer<'a, Chan: Channel, const CH: usize> {
+    index: usize,
+    audio: &'a mut Audio<Chan, CH>,
+}
+
+#[allow(single_use_lifetimes)]
+impl<'a, Chan: Channel, const CH: usize> Mixer<'a, Chan, CH> {
+    #[inline(always)]
+    fn new(audio: &'a mut Audio<Chan, CH>) -> Self {
+        let index = 0;
+
+        Mixer { index, audio }
+    }
+}
+
+// Using '_ results in reserved lifetime error.
+#[allow(single_use_lifetimes)]
+impl<'a, Chan: Channel, const CH: usize> Sink<Chan, CH>
+    for Mixer<'a, Chan, CH>
+{
+    #[inline(always)]
+    fn sample_rate(&self) -> NonZeroU32 {
+        self.audio.sample_rate()
+    }
+
+    #[inline(always)]
+    fn len(&self) -> usize {
+        self.audio.len()
+    }
+
+    #[inline(always)]
+    fn sink_with(&mut self, iter: &mut dyn Iterator<Item = Frame<Chan, CH>>) {
+        let mut this = self;
+        Sink::<Chan, CH>::sink_with(&mut this, iter)
+    }
+}
+
+impl<Chan: Channel, const CH: usize> Sink<Chan, CH>
+    for &mut Mixer<'_, Chan, CH>
+{
+    #[inline(always)]
+    fn sample_rate(&self) -> NonZeroU32 {
+        self.audio.sample_rate()
+    }
+
+    #[inline(always)]
+    fn len(&self) -> usize {
+        self.audio.len()
+    }
+
+    #[inline(always)]
+    fn sink_with(&mut self, iter: &mut dyn Iterator<Item = Frame<Chan, CH>>) {
+        for frame in self.audio.iter_mut().skip(self.index) {
+            if let Some(other) = iter.next() {
+                for (channel, chan) in
+                    frame.channels_mut().iter_mut().zip(other.channels())
+                {
+                    *channel += *chan;
+                }
+            } else {
+                break;
+            }
+            self.index += 1;
+        }
+    }
+}
+
+fn load_file(in_hz: u32, in_file: &str) -> Audio<Ch32, 2> {
+    // Load file as f32 buffer.
+    let rawfile = std::fs::read(in_file).unwrap();
+    let mut audio = Vec::new();
+    for sample in rawfile.chunks(4) {
+        audio.push(f32::from_le_bytes(sample.try_into().unwrap()));
+    }
+    // Create type-safe audio type from f32 buffer.
+    Audio::with_f32_buffer(in_hz, audio)
+}
+
+fn save_file(name: &str, audio: &Audio<Ch32, 2>) -> std::io::Result<()> {
+    // Convert audio to byte buffer
+    let mut samples = Vec::<u8>::new();
+    for frame in audio.iter() {
+        for channel in frame.channels() {
+            samples.extend(channel.to_f32().to_le_bytes());
+        }
+    }
+    // Save byte buffer
+    std::fs::write(name, samples)
+}
+
+fn main() -> std::io::Result<()> {
+    // We are mixing file 1 audio down into file 2 audio.
+
+    // Load file 1
+    let source = load_file(44_100, "examples/44_1k.raw");
+    // Load file 2
+    let mut out = load_file(48_000, "examples/48k.raw");
+    // Create mixer sink over output buffer
+    let mut mixer = Mixer::new(&mut out);
+
+    // Create a stream to convert to 48k
+    let mut stream = Stream::<2>::new(48_000);
+    stream.pipe(&source, &mut mixer);
+    stream.flush(&mut mixer);
+
+    // Save the mixed audio
+    save_file("examples/output.raw", &out)
+}
diff --git a/src/math.rs b/src/math.rs
index 3247dfd..11ab8f7 100644
--- a/src/math.rs
+++ b/src/math.rs
@@ -9,7 +9,7 @@
 
 use core::ops::Rem;
 
-/// Floating point methods currently only availabe on std, that may be
+/// Floating point methods currently only available on std, that may be
 /// implemented with the libm crate as dependency of core in the future.
 pub(crate) trait Libm: Rem<Output = Self> + Sized {
     fn sin(self) -> Self;