feat(modulation): add envelopes, LFOs and modulation matrix

Source/LFO.h

@@ -0,0 +1,63 @@
+#pragma once
+
+#include <JuceHeader.h>
+#include "Params.h"
+
+namespace serum
+{
+
+// ===========================================================================
+// Free-running LFO with tempo sync, seven shapes (sine/tri/saw/square/S&H/
+// step-sequencer/freehand), adjustable phase, fade-in and start delay.
+// ===========================================================================
+class LFO
+{
+public:
+    static constexpr int kShapePoints = 64;
+
+    void prepare (double sampleRate) { sr = sampleRate; reset(); }
+    void reset();
+
+    void setParams (float rateNorm, bool sync, float beat, int shape, float phase,
+                    float fade, float delay);
+    void setTempo (double bpm) noexcept { tempo = bpm; }
+    void setShapeData (const std::vector<float>& data, int steps);
+
+    float process() noexcept;                 // advance and return current value
+    float getPhase() const noexcept { return (float) phase; }
+    float getValue() const noexcept { return value; }
+
+    const std::vector<float>& getShapeData() const noexcept { return shapeBuffer; }
+    int   getShapeSteps() const noexcept { return shapeSteps; }
+
+private:
+    double sr = 44100.0;
+    double tempo = 120.0;
+
+    double phase = 0.0;
+    double rateHz = 1.0;
+    float  value = 0.0f;
+
+    int    shape = 0;
+    bool   sync = false;
+    float  beat = 0.25f;
+
+    double delaySeconds = 0.0;
+    double fadeSeconds  = 0.0;
+    double delayCounter = 0.0;   // samples remaining before start
+    double fadeCounter  = 0.0;   // samples elapsed in fade
+    float  fadeVal      = 1.0f;
+    float  prevDelayParam = -1.0f;
+    float  prevFadeParam  = -1.0f;
+
+    std::vector<float> shapeBuffer;
+    int   shapeSteps = 16;
+
+    juce::Random rng;
+    float  holdValue = 0.0f;
+    double prevPhase = 0.0;
+
+    float shapeValue() noexcept;
+};
+
+} // namespace serum