implement envelopes

src/synth/Envelope.h

@@ -0,0 +1,54 @@
+
+#pragma once
+
+#include <cstdint>
+#include <algorithm>
+
+enum class State {
+    Idle,
+    Attack,
+    Sustain,
+    Decay,
+    Release
+};
+
+class Envelope {
+
+public:
+
+    Envelope();
+    ~Envelope() = default;
+
+    // setters
+    void setSampleRate(float sampleRate) { sampleRate_ = sampleRate; }
+    void setAttack(float seconds) { attack_ = std::max(seconds, 0.0001f); }
+    void setDecay(float seconds) { decay_ = std::max(seconds, 0.0001f); }
+    void setSustain(float level) { sustain_ = level; }
+    void setRelease(float seconds) { release_ = std::max(seconds, 0.0001f); }
+    // values close to zero introduce that popping sound on noteOn/noteOffs
+
+    // note events
+    void noteOn();
+    void noteOff();
+
+    // return current level
+    float process(); 
+
+    // determine if a note is playing or not
+    bool isActive() const { return state_ != State::Idle; } 
+
+private:
+    
+    State state_ = State::Idle;
+
+    float sampleRate_ = 44100.0f;
+
+    float attack_ = 0.05f; // seconds
+    float decay_ = 0.2f; // seconds
+    float sustain_ = 0.7f; // level
+    float release_ = 0.2f; // seconds
+
+    float value_ = 0.0f;
+
+};
+