added midi synth base class and voice allocator

synth/midi_synth.h

@@ -0,0 +1,93 @@
+#pragma once
+#include <memory>
+#include <vector>
+#include "note_event.h"
+#include "voice_allocator.h"
+
+namespace trnr::lib::synth {
+
+// a generic midi synth base class with sample accurate event handling.
+template <typename t_synth>
+class midi_synth : public voice_allocator<t_synth> {
+public:
+    midi_synth(int _n_voices, double _samplerate, int _block_size)
+        : m_samplerate { _samplerate }
+        , m_block_size { _block_size }
+        , m_voices_active { false }
+    {
+    }
+
+    void set_samplerate(double _samplerate, int _block_size)
+    {
+        m_samplerate = _samplerate;
+        m_block_size = _block_size;
+        voice_allocator::set_samplerate(_samplerate);
+    }
+
+    void process_block(double* _output, int _n_frames)
+    {
+        // sample accurate event handling based on the iPlug2 synth by Oli Larkin
+        if (m_voices_active || !m_event_queue.empty()) {
+            int block_size = m_block_size;
+            int samples_remaining = _n_frames;
+            int start_index = 0;
+
+            while (samples_remaining > 0) {
+
+                if (samples_remaining < block_size)
+                    block_size = samples_remaining;
+
+                while (!m_event_queue.empty()) {
+                    note_event event = m_event_queue.front();
+
+                    // we assume the messages are in chronological order. If we find one later than the current block we are done.
+                    if (event.offset > start_index + block_size)
+                        break;
+
+                    // send performance messages to the voice allocator
+                    // message offset is relative to the start of this process_samples() block
+                    event.offset -= start_index;
+                    voice_allocator::add_event(event);
+
+                    m_event_queue.erase(m_event_queue.begin());
+                }
+
+                voice_allocator::process_samples(_output, start_index, block_size);
+
+                samples_remaining -= block_size;
+                start_index += block_size;
+            }
+
+            voices_active = voice_allocator::voices_active();
+
+            flush_event_queue(_n_frames);
+        } else {
+            for (int s = 0; s < _n_frames; s++) {
+                outputs[0][s] = 0.;
+                outputs[1][s] = 0.;
+            }
+        }
+    }
+    
+    void add_event(note_event event)
+    {
+        if (event.type == note_event_type::note_on)
+            m_voices_active = true;
+
+        m_event_queue.push_back(event);
+    }
+
+    void flush_event_queue(int frames)
+    {
+        for (int i = 0; i < m_event_queue.size(); i++) {
+            m_event_queue.at(i).offset -= frames;
+        }
+    }
+
+private:
+    std::vector<note_event> m_event_queue;
+    double m_samplerate;
+    int m_block_size;
+    bool m_voices_active;
+};
+}