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use super::{Millisecond, Amplitude, SamplesPerSecond};
pub struct Envelope {
pub attack: Vec<Amplitude>,
pub decay: Vec<Amplitude>,
pub release: Vec<Amplitude>,
}
impl Envelope {
pub fn new(
attack: Millisecond, decay: Millisecond, sustain: Amplitude, release: Millisecond, sample_rate: SamplesPerSecond
) -> Self {
let attack = interpolate(0.0, 1.0, ms_to_samples(attack, sample_rate));
let decay = interpolate(1.0, sustain, ms_to_samples(decay, sample_rate));
let release = interpolate(sustain, 0.0, ms_to_samples(release, sample_rate));
Self{attack, decay, release}
}
pub fn len(&self) -> usize {
self.attack.len() + self.decay.len() + self.release.len()
}
}
fn interpolate(start: Amplitude, end: Amplitude, milliseconds: Millisecond) -> Vec<Amplitude> {
let step_size = (end - start) / milliseconds as f32;
let mut amps = vec!();
let mut current_val = start + step_size;
for i in 0..=milliseconds {
if i == 0 {
amps.push(start)
} else if i == milliseconds {
amps.push(end)
} else {
amps.push(current_val);
current_val += step_size;
}
}
amps
}
fn ms_to_samples(ms: Millisecond, sample_rate: SamplesPerSecond) -> u32 {
let multiplier = sample_rate as u32 / 1000;
multiplier * ms
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn it_has_expected_total_length() {
let expected = 3 + ms_to_samples(30, 48000.0) as usize;
let total = Envelope::new(10, 10, 1.0, 10, 48000.0).len();
assert_eq! (expected, total)
}
#[test]
fn interpolate_works() {
let expected = vec![0.0, 0.2, 0.4, 0.6, 0.8, 1.0];
let result = interpolate(0.0, 1.0, 5);
assert_eq!(expected, result)
}
}
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