nooise 2.5.3

Ambient music generator for the terminal
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//! The Perc voice: white-noise hits on a grid.

use super::*;

/// Headroom trim on filtered-noise output, not a character control —
/// `perc.level` at 100% should reach close to full scale on its own (for a
/// single hit / continuous mode), leaving overlap safety margin to the
/// master bus's soft-clip/compressor plus `mix_voices`'s own perc weight.
const OUTPUT_TRIM: f32 = 0.5;

pub(crate) struct PercEngine {
    pub(crate) sample_rate: f32,
    pub(crate) trigger: GridTrigger,
    pub(crate) hits: Vec<NoiseHit>,
    pub(crate) noise: WhiteNoise,
    pub(crate) rng: StdRng,
}

impl PercEngine {
    pub(crate) fn new(sample_rate: f32) -> Self {
        Self {
            sample_rate,
            trigger: GridTrigger::new(),
            hits: Vec::with_capacity(8),
            noise: WhiteNoise::new(),
            rng: StdRng::from_entropy(),
        }
    }

    pub(crate) fn next(&mut self, c: &PercControls, timing: TimingContext) -> f32 {
        if c.interval_beats >= 4.25 {
            // Continuous mode: bypass GridTrigger/NoiseHit entirely so there is
            // no trigger-rate amplitude ripple to disguise (see GOTCHAS.md).
            // Reuse the same exponential smoothing transform as discrete hits so
            return self.noise.next(&mut self.rng) * c.level * OUTPUT_TRIM;
        }

        if self
            .trigger
            .pop_swung(timing, c.interval_beats, c.offset_beats, c.swing)
        {
            self.hits
                .push(NoiseHit::new(c.level, c.decay_ms, self.sample_rate));
        }

        let rng = &mut self.rng;
        mix_and_retain_mono(&mut self.hits, |h| h.next(rng), NoiseHit::is_done)
    }
}

pub(crate) struct NoiseHit {
    pub(crate) noise: WhiteNoise,
    pub(crate) samples_remaining: u64,
    pub(crate) total_samples: u64,
    pub(crate) level: f32,
}

impl NoiseHit {
    pub(crate) fn new(level: f32, decay_ms: f32, sample_rate: f32) -> Self {
        let total = (decay_ms * 0.001 * sample_rate).round() as u64;
        Self {
            noise: WhiteNoise::new(),
            samples_remaining: total,
            total_samples: total,
            level,
        }
    }
    pub(crate) fn next<R: Rng>(&mut self, rng: &mut R) -> f32 {
        if self.samples_remaining == 0 {
            return 0.0;
        }
        let gain = self.samples_remaining as f32 / self.total_samples as f32;
        self.samples_remaining -= 1;
        self.noise.next(rng) * gain * self.level * OUTPUT_TRIM
    }
    pub(crate) fn is_done(&self) -> bool {
        self.samples_remaining == 0
    }
}