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 ++++++++++++++++++++++++++++++++++++++++---------
 klangfarbrs/src/lib.rs  | 48 +++++++++++++++++++++++++++++++------------
 2 files changed, 79 insertions(+), 23 deletions(-)

(limited to 'klangfarbrs')

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)
     }
 }
diff --git a/klangfarbrs/src/lib.rs b/klangfarbrs/src/lib.rs
index 0fc7936..ef9417c 100644
--- a/klangfarbrs/src/lib.rs
+++ b/klangfarbrs/src/lib.rs
@@ -47,10 +47,7 @@ pub struct MonoSynth {
     pub continuous: bool,
     pub duration: Millisecond,
     // ADSR amplifier
-    pub attack: Millisecond,
-    pub decay: Millisecond,
-    pub sustain: Amplitude,
-    pub release: Millisecond,
+    envelope: Envelope,
     // filter
     pub cutoff: Hz,
     // pub resonance:
@@ -59,6 +56,7 @@ pub struct MonoSynth {
     pub fm_frequency: Hz,
     pub fm_depth: Amplitude,
     fm_phasor: Phasor,
+    current_envelope_position: usize,
 }
 
 pub struct Phasor {
@@ -113,15 +111,13 @@ impl MonoSynth {
             phasor_bend: Vector2::new(0.0, 0.0),
             continuous: true,
             duration: 0,
-            attack: 0,
-            decay: 0,
-            sustain: 0.0,
-            release: 0,
+            envelope: Envelope::new(500, 1000, 0.5, 4000, 48000.0),
             cutoff: 0.0,
             frequency_modulation: false,
             fm_frequency: 10.0,
             fm_depth: 0.1,
-            fm_phasor: Phasor { phase: 0.0 }
+            fm_phasor: Phasor { phase: 0.0 },
+            current_envelope_position: 0,
         }
     }
 
@@ -155,6 +151,11 @@ impl MonoSynth {
         self.frequency = frequency
     }
 
+    #[export]
+    fn continuous(&mut self, _owner: &Node, state: bool) {
+        self.continuous = state;
+    }
+
     #[export]
     fn phasor_bend(&mut self, _owner: &Node, phasor_bend: Vector2) {
         self.phasor_bend = phasor_bend
@@ -185,11 +186,12 @@ impl MonoSynth {
         self.fm_depth = fm_depth
     }
 
+    #[export]
     fn envelope(
-        &self, _owner: &Node,
+        &mut self, _owner: &Node,
         attack: Millisecond, decay: Millisecond, sustain: Amplitude, release: Millisecond
-    ) -> Envelope {
-        Envelope::new(attack, decay, sustain, release)
+    ) {
+        self.envelope = Envelope::new(attack, decay, sustain, release, self.sample_rate);
     }
 
     #[export]
@@ -197,7 +199,7 @@ impl MonoSynth {
         let mut frames = TypedArray::new();
 
         for _i in 0..samples {
-            let sample = Osc::generate_sample(&self.waveform, self.phasor.phase);
+            let mut sample = Osc::generate_sample(&self.waveform, self.phasor.phase);
             let next_phase : f32;
 
             if self.frequency_modulation {
@@ -214,6 +216,26 @@ impl MonoSynth {
                 self.phasor.phase = next_phase;
             }
 
+            if !self.continuous {
+                let pos = self.current_envelope_position;
+                let atk = self.envelope.attack.len();
+                let atkdcy = atk + self.envelope.decay.len();
+
+                if pos < atk {
+                    sample = sample * self.envelope.attack[pos]
+                } else if pos >= atk && pos < atkdcy  {
+                    sample = sample * self.envelope.decay[pos - atk]
+                } else if pos < self.envelope.len() {
+                    sample = sample * self.envelope.release[pos - atkdcy]
+                }
+
+                self.current_envelope_position += 1;
+
+                if self.current_envelope_position >= self.envelope.len() {
+                    self.current_envelope_position = 0;
+                }
+            }
+
             frames.push(Vector2::new(sample, sample));
         }
 
-- 
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