implement envelopes

src/synth/Envelope.cpp

@@ -0,0 +1,52 @@
+
+#include "Envelope.h"
+
+Envelope::Envelope() {
+
+}
+
+void Envelope::noteOn() {
+    state_ = State::Attack;
+}
+
+void Envelope::noteOff() {
+    if(state_ != State::Idle) state_ = State::Release;
+}
+
+float Envelope::process() {
+    
+    switch (state_) {
+      case State::Idle:
+        value_ = 0.0f;
+        break;
+      case State::Attack:
+        value_ += 1.0f / (attack_ * sampleRate_);
+        if(value_ >= 1.0f) {
+            value_ = 1.0f;
+            state_ = State::Decay;
+        }
+        break;
+      case State::Decay:
+        value_ -= (1.0f - sustain_) / (decay_ * sampleRate_);
+        if(value_ <= sustain_) {
+            value_ = sustain_;
+            state_ = State::Sustain;
+        }
+        break;
+      case State::Sustain:
+        // wait until release
+        break;
+      case State::Release:
+        value_ -= sustain_ / (release_ * sampleRate_);
+        if(value_ <= 0.0f) {
+            value_ = 0.0f;
+            state_ = State::Idle;
+        }
+        break;
+      default: // unreachable
+        break;
+    }
+
+    return value_;
+}
+