nooise 2.5.2

Ambient music generator for the terminal
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//! The Clap voice: a burst of several noise slaps per hit.

use super::*;

/// Headroom trim on the summed burst output, not a character control —
/// `clap.level` at 100% should reach close to full scale on its own. Kept
/// below `perc`'s trim since up to `slap_count` (max 8) bursts can overlap
/// and sum before this scale is applied, unlike perc's single hit stream.
const OUTPUT_TRIM: f32 = 0.42;

pub(crate) struct ClapEngine {
    pub(crate) sample_rate: f32,
    pub(crate) trigger: GridTrigger,
    pub(crate) voices: Vec<ClapVoice>,
    pub(crate) rng: StdRng,
}

impl ClapEngine {
    pub(crate) fn new(sample_rate: f32) -> Self {
        Self {
            sample_rate,
            trigger: GridTrigger::new(),
            voices: Vec::with_capacity(4),
            rng: StdRng::from_entropy(),
        }
    }

    pub(crate) fn next(&mut self, c: &ClapControls, timing: TimingContext) -> (f32, f32) {
        if self
            .trigger
            .pop_swung(timing, c.interval_beats, c.offset_beats, c.swing)
        {
            self.voices
                .push(ClapVoice::new(c, self.sample_rate, &mut self.rng));
        }

        let rng = &mut self.rng;
        let dry = mix_and_retain_mono(&mut self.voices, |v| v.next(rng), ClapVoice::is_done);
        (dry, dry)
    }
}

pub(crate) struct ClapVoice {
    pub(crate) noise: WhiteNoise,
    pub(crate) scheduled: Vec<u64>,
    pub(crate) bursts: Vec<ClapBurst>,
    pub(crate) current: u64,
    pub(crate) decay_samples: u64,
    pub(crate) filter_smoothing: f32,
    pub(crate) body_coeff: f32,
    pub(crate) body_state: f32,
    pub(crate) level: f32,
}

impl ClapVoice {
    pub(crate) fn new(c: &ClapControls, sample_rate: f32, rng: &mut StdRng) -> Self {
        let count = c.slap_count.round().max(1.0) as usize;
        let spread = (c.slap_spread_ms * 0.001 * sample_rate) as u64;
        let mut scheduled: Vec<u64> = (0..count)
            .map(|i| {
                if i == 0 {
                    0
                } else {
                    rng.gen_range(0..=spread.max(1))
                }
            })
            .collect();
        scheduled.sort_unstable();
        Self {
            noise: WhiteNoise::new(),
            scheduled,
            bursts: Vec::new(),
            current: 0,
            decay_samples: (c.decay_ms * 0.001 * sample_rate).round() as u64,
            filter_smoothing: noise_filter_smoothing(c.filter),
            body_coeff: c.body * 0.08,
            body_state: 0.0,
            level: c.level,
        }
    }

    pub(crate) fn next<R: Rng>(&mut self, rng: &mut R) -> f32 {
        self.scheduled.retain(|&t| {
            if self.current >= t {
                self.bursts.push(ClapBurst {
                    remaining: self.decay_samples,
                    total: self.decay_samples,
                });
                false
            } else {
                true
            }
        });

        if self.bursts.is_empty() && self.scheduled.is_empty() {
            return 0.0;
        }

        let mut out = 0.0f32;
        for burst in &mut self.bursts {
            if burst.remaining > 0 {
                let env = (burst.remaining as f32 / burst.total as f32).sqrt();
                burst.remaining -= 1;
                let raw = self.noise.next_filtered(rng, self.filter_smoothing);
                self.body_state += self.body_coeff * (raw - self.body_state);
                out += (raw + self.body_state) * env;
            }
        }
        self.bursts.retain(|b| b.remaining > 0);

        self.current += 1;
        out * self.level * OUTPUT_TRIM
    }

    pub(crate) fn is_done(&self) -> bool {
        self.scheduled.is_empty() && self.bursts.is_empty()
    }
}

pub(crate) struct ClapBurst {
    pub(crate) remaining: u64,
    pub(crate) total: u64,
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn swing_delays_the_claps_odd_subdivision() {
        let mut clap = ClapEngine::new(48_000.0);
        let controls = ClapControls {
            level: 1.0,
            interval_beats: 0.5,
            swing: 1.0,
            ..ClapControls::default()
        };

        clap.next(&controls, TimingContext::new(48_000.0, 120.0, 0.0));
        clap.next(&controls, TimingContext::new(48_000.0, 120.0, 0.5));
        assert_eq!(clap.voices.len(), 1);

        clap.next(&controls, TimingContext::new(48_000.0, 120.0, 0.75));
        assert_eq!(clap.voices.len(), 2);
    }
}