Libraries: Add LibDSP

LibDSP is a library for digital signal processing, and is primarily
intended to support the future DAW version of Piano.

Userland/Libraries/LibDSP/Track.h

@@ -0,0 +1,73 @@
+/*
+ * Copyright (c) 2021, kleines Filmröllchen <malu.bertsch@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include "Clip.h"
+#include "Music.h"
+#include "Processor.h"
+#include <LibCore/Object.h>
+
+namespace LibDSP {
+
+// A track is also known as a channel and serves as a container for the audio pipeline: clips -> processors -> mixing & output
+class Track : public Core::Object {
+    C_OBJECT_ABSTRACT(Track)
+public:
+    Track(NonnullRefPtr<Transport> transport)
+        : m_transport(move(transport))
+    {
+    }
+    virtual ~Track() override = default;
+
+    virtual bool check_processor_chain_valid() const = 0;
+    bool add_processor(NonnullRefPtr<Processor> new_processor);
+
+    // Creates the current signal of the track by processing current note or audio data through the processing chain
+    Sample current_signal();
+
+    NonnullRefPtrVector<Processor> const& processor_chain() const { return m_processor_chain; }
+    NonnullRefPtr<Transport> const transport() const { return m_transport; }
+
+protected:
+    bool check_processor_chain_valid_with_initial_type(SignalType initial_type) const;
+
+    // Subclasses override to provide the base signal to the processing chain
+    virtual Signal current_clips_signal() = 0;
+
+    NonnullRefPtrVector<Processor> m_processor_chain;
+    NonnullRefPtr<Transport> const m_transport;
+};
+
+class NoteTrack final : public Track {
+public:
+    virtual ~NoteTrack() override = default;
+
+    bool check_processor_chain_valid() const override;
+    NonnullRefPtrVector<NoteClip> const& clips() const { return m_clips; }
+
+protected:
+    virtual Signal current_clips_signal() override;
+
+private:
+    NonnullRefPtrVector<NoteClip> m_clips;
+};
+
+class AudioTrack final : public Track {
+public:
+    virtual ~AudioTrack() override = default;
+
+    bool check_processor_chain_valid() const override;
+    NonnullRefPtrVector<AudioClip> const& clips() const { return m_clips; }
+
+protected:
+    virtual Signal current_clips_signal() override;
+
+private:
+    NonnullRefPtrVector<AudioClip> m_clips;
+};
+
+}