librespot/playback/src/mixer/alsamixer.rs

use super::Mixer;
use super::AudioFilter;

use alsa;

#[derive(Clone)]
pub struct AlsaMixer {
    card: String,
    mixer: String,
}

// Doesn't work - Selem is borrowed from Mixer
// impl AlsaMixer {
//     fn get_selem(&self ) -> Result<(alsa::mixer::Selem), Box<Error>> {
//
//         let selem_id = alsa::mixer::SelemId::new(self.mixer, 0);
//         let mixer = alsa::mixer::Mixer::new(self.card, false)?;
//         let selem = mixer.find_selem(&selem_id).unwrap();
//
//         Ok((selem))
//     }
// }

impl Mixer for AlsaMixer {
    fn open(device: Option<String>) -> AlsaMixer {
        let card = device.unwrap_or(String::from("default"));
        let mixer = String::from("PCM");
        AlsaMixer {
            card: card,
            mixer: mixer,
        }
    }

    fn start(&self) {
    }

    fn stop(&self) {
    }

    fn volume(&self) -> u16 {
        let mixer = alsa::mixer::Mixer::new(&self.card, false).unwrap();
        let selem_id = alsa::mixer::SelemId::new(&self.mixer, 0);
        let selem = mixer.find_selem(&selem_id).unwrap();
        let (min, max) = selem.get_playback_volume_range();
        let volume: i64 = selem.get_playback_volume(alsa::mixer::SelemChannelId::FrontLeft).unwrap();

        // Spotify uses a volume range from 0 to 65535, but the ALSA mixers resolution might
        // differ, e.g. most ALSA mixers uses a resolution of 256. Therefore, we have to calculate
        // the multiplier to use, to get the corresponding Spotify volume value from the ALSA
        // mixers volume.
        let resolution = max - min + 1;
        let multiplier: u16 = (((0xFFFF + 1) / resolution) - 1) as u16;

        volume as u16 * multiplier
    }

    fn set_volume(&self, volume: u16) {
        let mixer = alsa::mixer::Mixer::new(&self.card, false).unwrap();
        let selem_id = alsa::mixer::SelemId::new(&self.mixer, 0);
        let selem = mixer.find_selem(&selem_id).unwrap();
        let (min, max) = selem.get_playback_volume_range();

        // Spotify uses a volume range from 0 to 65535, but the ALSA mixers resolution might
        // differ, e.g. most ALSA mixers uses a resolution of 256. Therefore, we have to calculate
        // the factor to use, to get the corresponding ALSA mixers volume value from the Spotify
        // volume.
        let resolution = max - min + 1;
        let factor: u16 = (((0xFFFF + 1) / resolution) - 1) as u16;
        let volume: i64 = (volume / factor) as i64;
        info!("Setting volume: {:?}", volume);
        selem.set_playback_volume_all(volume).unwrap();
    }

    fn get_audio_filter(&self) -> Option<Box<AudioFilter + Send>> {
        None
    }
}