Add a listener of voice state changes

src/sfizz/Synth.cpp

@@ -44,6 +44,13 @@ sfz::Synth::~Synth()
     resources.filePool.emptyFileLoadingQueues();
 }
 
+void sfz::Synth::onVoiceStateChanged(int idNumber, Voice::State state)
+{
+    (void)idNumber;
+    (void)state;
+    DBG("Voice " << idNumber << ": state " << static_cast<int>(state));
+}
+
 void sfz::Synth::onParseFullBlock(const std::string& header, const std::vector<Opcode>& members)
 {
     switch (hash(header)) {
@@ -1094,8 +1101,11 @@ void sfz::Synth::resetVoices(int numVoices)
     voices.clear();
     voices.reserve(numVoices);
 
-    for (int i = 0; i < numVoices; ++i)
-        voices.push_back(absl::make_unique<Voice>(i, resources));
+    for (int i = 0; i < numVoices; ++i) {
+        auto voice = absl::make_unique<Voice>(i, resources);
+        voice->setStateListener(this);
+        voices.emplace_back(std::move(voice));
+    }
 
     voiceViewArray.clear();
     voiceViewArray.reserve(numVoices);

src/sfizz/Synth.h

@@ -60,7 +60,7 @@ namespace sfz {
  * The jack_client.cpp file contains examples of the most classical usage of the
  * synth and can be used as a reference.
  */
-class Synth final : public Parser::Listener {
+class Synth final : public Voice::StateListener, public Parser::Listener {
 public:
     /**
      * @brief Construct a new Synth object with no voices. If you want sound
@@ -493,6 +493,12 @@ public:
      */
     const std::vector<CCNamePair>& getCCLabels() const noexcept { return ccLabels; }
 
+protected:
+    /**
+     * @brief The voice callback which is called during a change of state.
+     */
+    void onVoiceStateChanged(int idNumber, Voice::State state) override;
+
 protected:
     /**
      * @brief The parser callback; this is called by the parent object each time

src/sfizz/Voice.cpp

@@ -15,7 +15,7 @@
 #include "absl/algorithm/container.h"
 
 sfz::Voice::Voice(int voiceNumber, sfz::Resources& resources)
-: voiceNumber(voiceNumber), resources(resources)
+: voiceNumber(voiceNumber), stateListener(nullptr), resources(resources)
 {
     filters.reserve(config::filtersPerVoice);
     equalizers.reserve(config::eqsPerVoice);
@@ -36,7 +36,7 @@ void sfz::Voice::startVoice(Region* region, int delay, int number, float value,
     triggerValue = value;
 
     this->region = region;
-    state = State::playing;
+    switchState(State::playing);
 
     ASSERT(delay >= 0);
     if (delay < 0)
@@ -647,7 +647,7 @@ bool sfz::Voice::checkOffGroup(int delay, uint32_t group) noexcept
 
 void sfz::Voice::reset() noexcept
 {
-    state = State::idle;
+    switchState(State::idle);
     region = nullptr;
     currentPromise.reset();
     sourcePosition = 0;
@@ -766,3 +766,13 @@ void sfz::Voice::updateChannelPowers(AudioSpan<float> buffer)
                 channelEnvelopeFilters[i].tickLowpass(std::abs(input[s]));
     }
 }
+
+
+void sfz::Voice::switchState(State s)
+{
+    if (s != state) {
+        state = s;
+        if (stateListener)
+            stateListener->onVoiceStateChanged(voiceNumber, s);
+    }
+}

src/sfizz/Voice.h

@@ -48,6 +48,22 @@ public:
     {
         return voiceNumber;
     }
+
+    enum class State {
+        idle,
+        playing
+    };
+
+    class StateListener {
+    public:
+        virtual void onVoiceStateChanged(int /*idNumber*/, State /*state*/) {}
+    };
+
+    /**
+     * @brief Sets the listener which is called when the voice state changes.
+     */
+    void setStateListener(StateListener *l) noexcept { stateListener = l; }
+
     /**
      * @brief Change the sample rate of the voice. This is used to compute all
      * pitch related transformations so it needs to be propagated from the synth
@@ -278,14 +294,16 @@ private:
     void setupOscillatorUnison();
     void updateChannelPowers(AudioSpan<float> buffer);
 
+    /**
+     * @brief Modify the voice state and notify any listeners.
+     */
+    void switchState(State s);
+
     const int voiceNumber {};
+    StateListener* stateListener = nullptr;
 
     Region* region { nullptr };
 
-    enum class State {
-        idle,
-        playing
-    };
     State state { State::idle };
     bool noteIsOff { false };