From a17829f5412ee0757574b34e34ce78b2975df1fe Mon Sep 17 00:00:00 2001
From: Grant Shangreaux <grant@unabridgedsoftware.com>
Date: Thu, 11 Nov 2021 10:20:59 -0600
Subject: Add: poorly implemented but working amplitude envelope

---
 klangfarbrs/src/adsr.rs | 54 ++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 44 insertions(+), 10 deletions(-)

(limited to 'klangfarbrs/src/adsr.rs')

diff --git a/klangfarbrs/src/adsr.rs b/klangfarbrs/src/adsr.rs
index 682cc8a..9d51ba3 100644
--- a/klangfarbrs/src/adsr.rs
+++ b/klangfarbrs/src/adsr.rs
@@ -1,16 +1,18 @@
-use crate::{Millisecond, Amplitude};
+use super::{Millisecond, Amplitude, SamplesPerSecond};
 
 pub struct Envelope {
-    attack: Vec<Amplitude>,
-    decay: Vec<Amplitude>,
-    release: Vec<Amplitude>,
+    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) -> Self {
-        let attack = vec![sustain; attack as usize];
-        let decay = vec![sustain; decay as usize];
-        let release = vec![sustain; release as usize];
+    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}
     }
@@ -20,13 +22,45 @@ impl Envelope {
     }
 }
 
+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 total = Envelope::new(10, 10, 1.0, 10).len();
-        assert_eq! (30, total)
+        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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