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

Source/ModulationMatrix.h

@@ -0,0 +1,43 @@
+#pragma once
+
+#include <JuceHeader.h>
+#include "Params.h"
+
+namespace serum
+{
+
+// ===========================================================================
+// A single modulation connection: source -> target with a static depth and a
+// bipolar flag. One level of modulation only (no modulation of modulation).
+// ===========================================================================
+struct ModConnection
+{
+    ModSource source   = ModSource::Lfo1;
+    ModTarget target   = ModTarget::None;
+    float     depth    = 0.0f;
+    bool      bipolar  = false;
+};
+
+// ===========================================================================
+// Ordered collection of modulation connections. Serialisable to/from a
+// juce::ValueTree so that connections survive preset save/load.
+// ===========================================================================
+class ModulationMatrix
+{
+public:
+    static constexpr int kMaxConnections = 32;
+
+    std::vector<ModConnection> connections;
+
+    bool addConnection (ModSource source, ModTarget target, float depth, bool bipolar);
+    void removeConnection (int index);
+    void removeAllWithTarget (ModTarget target);
+    void clear() { connections.clear(); }
+
+    int  size() const noexcept { return (int) connections.size(); }
+
+    juce::ValueTree toValueTree() const;
+    void fromValueTree (const juce::ValueTree& tree);
+};
+
+} // namespace serum