Voice Rework -- Events, Track Queues (#806)

This implements a proof-of-concept for an improved audio frontend. The largest change is the introduction of events and event handling: both by time elapsed and by track events, such as ending or looping. Following on from this, the library now includes a basic, event-driven track queue system (which people seem to ask for unusually often). A new sample, `examples/13_voice_events`, demonstrates both the `TrackQueue` system and some basic events via the `~queue` and `~play_fade` commands.

Locks are removed from around the control of `Audio` objects, which should allow the backend to be moved to a more granular futures-based backend solution in a cleaner way.

utils/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "utils"
+version = "0.1.0"
+authors = ["Kyle Simpson <kyleandrew.simpson@gmail.com>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+byteorder = "1"

utils/README.md

@@ -0,0 +1 @@
+Test utilities for testing and benchmarking songbird.

utils/src/lib.rs

@@ -0,0 +1,67 @@
+use byteorder::{LittleEndian, WriteBytesExt};
+use std::mem;
+
+pub fn make_sine(float_len: usize, stereo: bool) -> Vec<u8> {
+    let sample_len = mem::size_of::<f32>();
+    let byte_len = float_len * sample_len;
+
+    // set period to 100 samples == 480Hz sine.
+
+    let mut out = vec![0u8; byte_len];
+    let mut byte_slice = &mut out[..];
+
+    for i in 0..float_len {
+        let x_val = (i as f32) * 50.0 / std::f32::consts::PI;
+        byte_slice.write_f32::<LittleEndian>(x_val.sin()).unwrap();
+    }
+
+    if stereo {
+        let mut new_out = vec![0u8; byte_len * 2];
+
+        for (mono_chunk, stereo_chunk) in out[..]
+            .chunks(sample_len)
+            .zip(new_out[..].chunks_mut(2 * sample_len))
+        {
+            stereo_chunk[..sample_len].copy_from_slice(mono_chunk);
+            stereo_chunk[sample_len..].copy_from_slice(mono_chunk);
+        }
+
+        new_out
+    } else {
+        out
+    }
+}
+
+pub fn make_pcm_sine(i16_len: usize, stereo: bool) -> Vec<u8> {
+    let sample_len = mem::size_of::<i16>();
+    let byte_len = i16_len * sample_len;
+
+    // set period to 100 samples == 480Hz sine.
+    // amplitude = 10_000
+
+    let mut out = vec![0u8; byte_len];
+    let mut byte_slice = &mut out[..];
+
+    for i in 0..i16_len {
+        let x_val = (i as f32) * 50.0 / std::f32::consts::PI;
+        byte_slice
+            .write_i16::<LittleEndian>((x_val.sin() * 10_000.0) as i16)
+            .unwrap();
+    }
+
+    if stereo {
+        let mut new_out = vec![0u8; byte_len * 2];
+
+        for (mono_chunk, stereo_chunk) in out[..]
+            .chunks(sample_len)
+            .zip(new_out[..].chunks_mut(2 * sample_len))
+        {
+            stereo_chunk[..sample_len].copy_from_slice(mono_chunk);
+            stereo_chunk[sample_len..].copy_from_slice(mono_chunk);
+        }
+
+        new_out
+    } else {
+        out
+    }
+}