Piano: Add Play/Pause, Forward and Back buttons

Piano now has a toolbar allowing the playback to be paused,
or to be stepped forward or back a note.

Userland/Applications/Piano/AudioPlayerLoop.h

@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) 2021, kleines Filmröllchen <malu.bertsch@gmail.com>
+ * Copyright (c) 2021, JJ Roberts-White <computerfido@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include "Music.h"
+#include <LibAudio/ClientConnection.h>
+#include <LibAudio/WavWriter.h>
+#include <LibCore/Object.h>
+
+class TrackManager;
+
+// Wrapper class accepting custom events to advance the track playing and forward audio data to the system.
+// This does not run on a separate thread, preventing IPC multithreading madness.
+class AudioPlayerLoop : public Core::Object {
+    C_OBJECT(AudioPlayerLoop)
+public:
+    AudioPlayerLoop(TrackManager& track_manager, bool& need_to_write_wav, Audio::WavWriter& wav_writer);
+
+    void enqueue_audio();
+
+    void toggle_paused();
+    bool is_playing() { return m_should_play_audio; }
+
+private:
+    TrackManager& m_track_manager;
+    Array<Sample, sample_count> m_buffer;
+    RefPtr<Audio::ClientConnection> m_audio_client;
+
+    bool m_should_play_audio = true;
+
+    bool& m_need_to_write_wav;
+    Audio::WavWriter& m_wav_writer;
+};