hellocpal.rs

//! Copyright (c) Jarkko Sakkinen 2021
//! 
//! A simple synthesis and playback test.

use cpal::Device;
use cpal::Sample;
use cpal::SampleFormat;
use cpal::StreamConfig;
use cpal::StreamError;
use cpal::traits::DeviceTrait;
use cpal::traits::HostTrait;
use cpal::traits::StreamTrait;
use libm::fmod;

fn main() {
    let host = cpal::default_host();

    let device = host
        .default_output_device()
        .expect("unable to find an output device");

    let config = device.default_output_config().unwrap();

    match config.sample_format() {
        SampleFormat::F32 => play::<f32>(&device, &config.into()),
        SampleFormat::I16 => play::<i16>(&device, &config.into()),
        SampleFormat::U16 => play::<u16>(&device, &config.into()),
    };
}

fn play<T: Sample>(device: &Device, config: &StreamConfig) -> () {
    let sample_rate = config.sample_rate.0 as u32;

    let mut sample = 0;
    let mut oscillator = move || {
        sample = (sample + 1) % sample_rate;

        let cycle = 1.0 / 55.0;
        let time = fmod(sample as f64 / sample_rate as f64, cycle);

        ((time / cycle) * 2.0 - 1.0) as f32
    };

    let channels = config.channels as usize;

    let stream = device
        .build_output_stream(
            config,
            move |data: &mut [T], _| data_callback(data, channels, &mut oscillator),
            error_callback,
        )
        .unwrap();

    stream.play().unwrap();   

    std::thread::sleep(std::time::Duration::from_secs(10));
}

fn data_callback<T: Sample>(output: &mut [T], channels: usize, oscillator: &mut dyn FnMut() -> f32)
{
    for frame in output.chunks_mut(channels) {
        let value: T = cpal::Sample::from::<f32>(&oscillator());
        for sample in frame.iter_mut() {
            *sample = value;
        }
    }
}

fn error_callback(err: StreamError) {
    eprintln!("{}", err);
}