ferretro/ferretro_components/src/provided/sdl2/audio.rs

use crate::prelude::*;

use std::mem::size_of;
use std::path::Path;

use sdl2::Sdl;
use sdl2::audio::{AudioCVT, AudioFormat, AudioFormatNum, AudioQueue, AudioSpec, AudioSpecDesired};

use crate::base::ControlFlow;

pub struct SimpleSdl2AudioQueueComponent {
    sdl_audio: sdl2::AudioSubsystem,
    src_freq: f64,
    audio_buffer: Vec<i16>,
    queue: Option<AudioQueue<i16>>,
    must_resample: bool,
    started: bool,
}

/// Work around an idiosyncrasy of the sdl2 crate's AudioCVT API.
///
/// It only deals in Vec<u8>, but from where I'm sitting it should really be abstracting away the
/// "u8" part if the rest of the API deals in the appropriate sample type.
pub(crate) fn resample<C: AudioFormatNum>(converter: &AudioCVT, mut samples: Vec<C>) -> Vec<C> {
    let sample_size = size_of::<C>();

    let ptr = samples.as_mut_ptr() as *mut u8;
    let length = samples.len() * sample_size;
    let capacity = samples.capacity() * sample_size;
    std::mem::forget(samples);
    let samples_u8 = unsafe { Vec::from_raw_parts(ptr, length, capacity) };

    let mut resampled_u8 = converter.convert(samples_u8);

    let ptr = resampled_u8.as_mut_ptr() as *mut C;
    let length = resampled_u8.len() / sample_size;
    let capacity = resampled_u8.capacity() / sample_size;
    std::mem::forget(resampled_u8);
    unsafe { Vec::from_raw_parts(ptr, length, capacity) }
}

pub(crate) fn make_converter(src_freq: f64, dest_spec: &AudioSpec) -> Result<AudioCVT, String> {
    // note on the `* 16`: as long as the ratio between src_rate and dst_rate is right,
    // we should be in the clear -- this is to make up for SDL not giving us floats for
    // this, we can at least get some quasi-fixed-point precision going on...
    AudioCVT::new(
        AudioFormat::s16_sys(),
        2,
        (src_freq * 16.0).round() as i32,
        dest_spec.format,
        dest_spec.channels,
        dest_spec.freq * 16,
    )
}

impl RetroCallbacks for SimpleSdl2AudioQueueComponent {
    fn video_refresh(&mut self, _frame: &VideoFrame) {
        self.started = true;
    }

    fn audio_samples(&mut self, stereo_pcm: &[i16]) -> usize {
        if self.started {
            self.audio_buffer.extend(stereo_pcm);
        }
        stereo_pcm.len() / 2
    }

    fn set_system_av_info(&mut self, av_info: &SystemAvInfo) -> Option<bool> {
        if let Some(queue) = &self.queue {
            if make_converter(av_info.timing.sample_rate, queue.spec()).is_ok() {
                self.src_freq = av_info.timing.sample_rate;
                Some(true)
            } else {
                Some(false)
            }
        } else {
            Some(false)
        }
    }
}

impl RetroComponent for SimpleSdl2AudioQueueComponent {
    fn post_load_game(&mut self, retro: &mut LibretroWrapper, _rom: &Path) -> crate::base::Result<()> {
        let timing = retro.get_system_av_info().timing;
        self.src_freq = timing.sample_rate;

        let samples_per_frame = timing.sample_rate / timing.fps;

        let desired_spec = AudioSpecDesired {
            freq: Some(self.src_freq.round() as i32),
            channels: Some(2),
            samples: Some((2.0 * samples_per_frame).ceil() as u16),
        };

        let queue = self.sdl_audio.open_queue(None, &desired_spec)?;
        if queue.spec().freq != desired_spec.freq.unwrap() {
            self.must_resample = true;
            eprintln!("warning: using naive resampling");
        }
        queue.resume();

        self.queue = Some(queue);
        self.started = false;
        Ok(())
    }

    fn post_run(&mut self, _retro: &mut LibretroWrapper) -> ControlFlow {
        if self.src_freq != 0.0 {
            let queue = self.queue.as_mut().unwrap();
            if self.must_resample {
                match make_converter(self.src_freq, queue.spec()) {
                    Ok(converter) => {
                        if !self.audio_buffer.is_empty() {
                            let mut samples = std::mem::take(&mut self.audio_buffer);
                            samples = resample(&converter, samples);
                            self.audio_buffer = samples;
                            queue.queue(&self.audio_buffer);
                            self.audio_buffer.clear();
                        }
                        ControlFlow::Continue
                    }
                    Err(e) => {
                        eprintln!("Audio sample rate conversion failed: {:?}", e);
                        ControlFlow::Break
                    }
                }
            } else {
                queue.queue(self.audio_buffer.as_slice());
                self.audio_buffer.clear();
                ControlFlow::Continue
            }
        } else {
            ControlFlow::Continue
        }
    }
}

impl SimpleSdl2AudioQueueComponent {
    pub fn new(sdl_context: &mut Sdl) -> crate::base::Result<Self> {
        let sdl_audio = sdl_context.audio()?;

        Ok(SimpleSdl2AudioQueueComponent {
            sdl_audio,
            src_freq: 32040.5, // nod to the old libsnes default til load_game or set_system_av_info
            audio_buffer: Default::default(),
            queue: None,
            must_resample: false,
            started: false,
        })
    }
}