LibDSP: Introduce the Keyboard

This is a class for handling user MIDI input, which is combined by the
Track with roll note data if applicable.

Userland/Libraries/LibDSP/Keyboard.cpp

@@ -0,0 +1,68 @@
+/*
+ * Copyright (c) 2021-2022, kleines Filmröllchen <filmroellchen@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "Keyboard.h"
+#include "Music.h"
+#include <AK/Error.h>
+#include <AK/NumericLimits.h>
+
+namespace LibDSP {
+
+void Keyboard::set_keyboard_note(u8 pitch, Keyboard::Switch note_switch)
+{
+    VERIFY(pitch < note_frequencies.size());
+
+    if (note_switch == Switch::Off) {
+        m_pressed_notes.remove(pitch);
+        return;
+    }
+
+    auto fake_note = RollNote {
+        .on_sample = m_transport->time(),
+        .off_sample = NumericLimits<u32>::max(),
+        .pitch = pitch,
+        .velocity = NumericLimits<i8>::max(),
+    };
+
+    m_pressed_notes.set(pitch, fake_note);
+}
+void Keyboard::set_keyboard_note_in_active_octave(i8 octave_offset, Switch note_switch)
+{
+    u8 real_note = octave_offset + (m_virtual_keyboard_octave - 1) * notes_per_octave;
+    set_keyboard_note(real_note, note_switch);
+}
+
+void Keyboard::change_virtual_keyboard_octave(Direction direction)
+{
+    if (direction == Direction::Up) {
+        if (m_virtual_keyboard_octave < octave_max)
+            ++m_virtual_keyboard_octave;
+    } else {
+        if (m_virtual_keyboard_octave > octave_min)
+            --m_virtual_keyboard_octave;
+    }
+}
+
+ErrorOr<void> Keyboard::set_virtual_keyboard_octave(u8 octave)
+{
+    if (octave <= octave_max && octave >= octave_min) {
+        m_virtual_keyboard_octave = octave;
+        return {};
+    }
+    return Error::from_string_literal("Octave out of range");
+}
+
+bool Keyboard::is_pressed(u8 pitch) const
+{
+    return m_pressed_notes.get(pitch).has_value() && m_pressed_notes.get(pitch)->is_playing(m_transport->time());
+}
+
+bool Keyboard::is_pressed_in_active_octave(i8 octave_offset) const
+{
+    return is_pressed(octave_offset + virtual_keyboard_octave_base());
+}
+
+}