prometeu-runtime/crates/prometeu-runtime-desktop/src/audio.rs

use prometeu_core::hardware::{AudioCommand, Channel, LoopMode, MAX_CHANNELS, OUTPUT_SAMPLE_RATE};
use cpal::traits::{DeviceTrait, HostTrait, StreamTrait};
use ringbuf::traits::{Consumer, Producer, Split};
use ringbuf::HeapRb;
use std::sync::Arc;
use std::time::Duration;

pub struct HostAudio {
    pub producer: Option<ringbuf::wrap::CachingProd<Arc<HeapRb<AudioCommand>>>>,
    pub perf_consumer: Option<ringbuf::wrap::CachingCons<Arc<HeapRb<u64>>>>,
    _stream: Option<cpal::Stream>,
}

impl HostAudio {
    pub fn new() -> Self {
        Self {
            producer: None,
            perf_consumer: None,
            _stream: None,
        }
    }

    pub fn init(&mut self) {
        let host = cpal::default_host();
        let device = host
            .default_output_device()
            .expect("no output device available");

        let config = cpal::StreamConfig {
            channels: 2,
            sample_rate: cpal::SampleRate(OUTPUT_SAMPLE_RATE),
            buffer_size: cpal::BufferSize::Default,
        };

        let rb = HeapRb::<AudioCommand>::new(1024);
        let (prod, mut cons) = rb.split();

        self.producer = Some(prod);

        let mut mixer = AudioMixer::new();

        // To pass performance data from the audio thread to the main thread
        let audio_perf_rb = HeapRb::<u64>::new(64);
        let (mut perf_prod, perf_cons) = audio_perf_rb.split();

        let stream = device
            .build_output_stream(
                &config,
                move |data: &mut [f32], _: &cpal::OutputCallbackInfo| {
                    // Consumes commands from ringbuffer
                    while let Some(cmd) = cons.try_pop() {
                        mixer.process_command(cmd);
                    }
                    // Mixes audio
                    mixer.fill_buffer(data);
                    // Sends processing time in microseconds
                    let _ = perf_prod.try_push(mixer.last_processing_time.as_micros() as u64);
                },
                |err| eprintln!("audio stream error: {}", err),
                None,
            )
            .expect("failed to build audio stream");

        stream.play().expect("failed to play audio stream");
        self._stream = Some(stream);
        self.perf_consumer = Some(perf_cons);
    }

    pub fn send_commands(&mut self, commands: &mut Vec<AudioCommand>) {
        if let Some(producer) = &mut self.producer {
            for cmd in commands.drain(..) {
                let _ = producer.try_push(cmd);
            }
        }
    }

    pub fn update_stats(&mut self, stats: &mut crate::stats::HostStats) {
        if let Some(cons) = &mut self.perf_consumer {
            while let Some(us) = cons.try_pop() {
                stats.record_audio_perf(us);
            }
        }
    }
}

pub struct AudioMixer {
    voices: [Channel; MAX_CHANNELS],
    pub last_processing_time: Duration,
}

impl AudioMixer {
    pub fn new() -> Self {
        Self {
            voices: Default::default(),
            last_processing_time: Duration::ZERO,
        }
    }

    pub fn process_command(&mut self, cmd: AudioCommand) {
        match cmd {
            AudioCommand::Play {
                sample,
                voice_id,
                volume,
                pan,
                pitch,
                priority,
                loop_mode,
            } => {
                if voice_id < MAX_CHANNELS {
                    self.voices[voice_id] = Channel {
                        sample: Some(sample),
                        pos: 0.0,
                        pitch,
                        volume,
                        pan,
                        loop_mode,
                        priority,
                    };
                }
            }
            AudioCommand::Stop { voice_id } => {
                if voice_id < MAX_CHANNELS {
                    self.voices[voice_id].sample = None;
                }
            }
            AudioCommand::SetVolume { voice_id, volume } => {
                if voice_id < MAX_CHANNELS {
                    self.voices[voice_id].volume = volume;
                }
            }
            AudioCommand::SetPan { voice_id, pan } => {
                if voice_id < MAX_CHANNELS {
                    self.voices[voice_id].pan = pan;
                }
            }
            AudioCommand::SetPitch { voice_id, pitch } => {
                if voice_id < MAX_CHANNELS {
                    self.voices[voice_id].pitch = pitch;
                }
            }
        }
    }

    pub fn fill_buffer(&mut self, buffer: &mut [f32]) {
        let start = std::time::Instant::now();
        // Zeroes the buffer (stereo)
        for sample in buffer.iter_mut() {
            *sample = 0.0;
        }

        for voice in self.voices.iter_mut() {
            let sample_data = match &voice.sample {
                Some(s) => s,
                None => continue,
            };

            let pitch_ratio = sample_data.sample_rate as f64 / OUTPUT_SAMPLE_RATE as f64;
            let step = voice.pitch * pitch_ratio;

            let vol_f = voice.volume as f32 / 255.0;
            let pan_f = voice.pan as f32 / 255.0;
            let vol_l = vol_f * (1.0 - pan_f).sqrt();
            let vol_r = vol_f * pan_f.sqrt();

            for frame in buffer.chunks_exact_mut(2) {
                let pos_int = voice.pos as usize;
                let pos_fract = voice.pos - pos_int as f64;

                if pos_int >= sample_data.data.len() {
                    voice.sample = None;
                    break;
                }

                // Linear Interpolation
                let s1 = sample_data.data[pos_int] as f32 / 32768.0;
                let s2 = if pos_int + 1 < sample_data.data.len() {
                    sample_data.data[pos_int + 1] as f32 / 32768.0
                } else if voice.loop_mode == LoopMode::On {
                    let loop_start = sample_data.loop_start.unwrap_or(0) as usize;
                    sample_data.data[loop_start] as f32 / 32768.0
                } else {
                    0.0
                };

                let sample_val = s1 + (s2 - s1) * pos_fract as f32;

                frame[0] += sample_val * vol_l;
                frame[1] += sample_val * vol_r;

                voice.pos += step;

                let end_pos = sample_data.loop_end.map(|e| e as f64).unwrap_or(sample_data.data.len() as f64);

                if voice.pos >= end_pos {
                    if voice.loop_mode == LoopMode::On {
                        let loop_start = sample_data.loop_start.unwrap_or(0) as f64;
                        voice.pos = loop_start + (voice.pos - end_pos);
                    } else {
                        voice.sample = None;
                        break;
                    }
                }
            }
        }

        // Final clamp to avoid clipping (optional if using f32, but good for fidelity)
        for sample in buffer.iter_mut() {
            *sample = sample.clamp(-1.0, 1.0);
        }
        self.last_processing_time = start.elapsed();
    }
}