decodable/
decodable.rs

1//! Shows how to create a custom [`Decodable`] type by implementing a Sine wave.
2
3use bevy::{
4    audio::{AddAudioSource, AudioPlugin, ChannelCount, SampleRate, Source, Volume},
5    math::ops,
6    prelude::*,
7    reflect::TypePath,
8};
9use core::time::Duration;
10
11// This struct usually contains the data for the audio being played.
12// This is where data read from an audio file would be stored, for example.
13// This allows the type to be registered as an asset.
14#[derive(Asset, TypePath)]
15struct SineAudio {
16    frequency: f32,
17}
18// This decoder is responsible for playing the audio,
19// and so stores data about the audio being played.
20struct SineDecoder {
21    // how far along one period the wave is (between 0 and 1)
22    current_progress: f32,
23    // how much we move along the period every frame
24    progress_per_frame: f32,
25    // how long a period is
26    period: f32,
27    sample_rate: SampleRate,
28}
29
30impl SineDecoder {
31    fn new(frequency: f32) -> Self {
32        // standard sample rate for most recordings
33        let sample_rate = 44_100;
34        SineDecoder {
35            current_progress: 0.,
36            progress_per_frame: frequency / sample_rate as f32,
37            period: std::f32::consts::PI * 2.,
38            sample_rate: SampleRate::new(sample_rate).unwrap(),
39        }
40    }
41}
42
43// The decoder must implement iterator so that it can implement `Decodable`.
44impl Iterator for SineDecoder {
45    type Item = f32;
46
47    fn next(&mut self) -> Option<Self::Item> {
48        self.current_progress += self.progress_per_frame;
49        // we loop back round to 0 to avoid floating point inaccuracies
50        self.current_progress %= 1.;
51        Some(ops::sin(self.period * self.current_progress))
52    }
53}
54// `Source` is what allows the audio source to be played by bevy.
55// This trait provides information on the audio.
56impl Source for SineDecoder {
57    fn current_span_len(&self) -> Option<usize> {
58        None
59    }
60
61    fn channels(&self) -> ChannelCount {
62        ChannelCount::new(1).unwrap()
63    }
64
65    fn sample_rate(&self) -> SampleRate {
66        self.sample_rate
67    }
68
69    fn total_duration(&self) -> Option<Duration> {
70        None
71    }
72}
73
74// Finally `Decodable` can be implemented for our `SineAudio`.
75impl Decodable for SineAudio {
76    type Decoder = SineDecoder;
77
78    fn decoder(&self) -> Self::Decoder {
79        SineDecoder::new(self.frequency)
80    }
81}
82
83fn main() {
84    let mut app = App::new();
85    // register the audio source so that it can be used
86    app.add_plugins(DefaultPlugins.set(AudioPlugin {
87        global_volume: Volume::Linear(0.2).into(),
88        ..default()
89    }))
90    .add_audio_source::<SineAudio>()
91    .add_systems(Startup, setup)
92    .run();
93}
94
95fn setup(mut assets: ResMut<Assets<SineAudio>>, mut commands: Commands) {
96    // add a `SineAudio` to the asset server so that it can be played
97    let audio_handle = assets.add(SineAudio {
98        frequency: 440., // this is the frequency of A4
99    });
100    commands.spawn(AudioPlayer(audio_handle));
101}
decodable/decodable.rs

decodable/
decodable.rs
