added simple keyboard control

src/NoteQueue.cpp

@@ -0,0 +1,23 @@
+
+#include "NoteQueue.h"
+
+bool NoteQueue::push(const NoteEvent& event) {
+    size_t head = head_.load(std::memory_order_relaxed);
+    size_t next = (head + 1) % SIZE;
+
+    if(next == tail_.load(std::memory_order_relaxed)) return false; // full
+
+    buffer_[head] = event;
+    head_.store(next, std::memory_order_relaxed);
+    return true;
+}
+
+bool NoteQueue::pop(NoteEvent& event) {
+    size_t tail = tail_.load(std::memory_order_relaxed);
+
+    if(tail == head_.load(std::memory_order_acquire)) return false; // empty
+
+    event = buffer_[tail];
+    tail_.store((tail + 1) % SIZE, std::memory_order_release);
+    return true;
+}

src/NoteQueue.h

@@ -0,0 +1,36 @@
+
+#pragma once
+
+#include <array>
+#include <atomic>
+#include <cstdint>
+
+enum class NoteEventType {
+    NoteOn,
+    NoteOff
+};
+
+struct NoteEvent {
+    NoteEventType type; // noteOn or noteOff
+    uint8_t note; // 0-128, a keyboard goes 0-87
+    float velocity; // 0-1, from a midi instrument its 0-127 though
+};
+
+// the queue is to keep track of note events from the UI/input thread to the audio engine thread
+class NoteQueue {
+
+public:
+    NoteQueue() = default;
+    ~NoteQueue() = default;
+
+    bool push(const NoteEvent& event);
+    bool pop(NoteEvent& event);
+
+private:
+    static constexpr size_t SIZE = 128;
+    
+    std::array<NoteEvent, SIZE> buffer_;
+    std::atomic<size_t> head_{ 0 };
+    std::atomic<size_t> tail_{ 0 };
+
+};