Piano: Handle octave slider jumps of greater than 1

The previous slider handler relied on the new value being 1 different
than the previous.

fixes #1163.

Applications/Piano/KnobsWidget.cpp

@@ -83,7 +83,7 @@ KnobsWidget::KnobsWidget(TrackManager& track_manager, MainWidget& main_widget)
     m_octave_knob->on_value_changed = [this](int value) {
         int new_octave = octave_max - value;
         if (m_change_underlying)
-            m_main_widget.set_octave_and_ensure_note_change(new_octave == m_track_manager.octave() + 1 ? Up : Down);
+            m_main_widget.set_octave_and_ensure_note_change(new_octave);
         ASSERT(new_octave == m_track_manager.octave());
         m_octave_value->set_text(String::number(new_octave));
     };

Applications/Piano/MainWidget.cpp

@@ -160,6 +160,16 @@ void MainWidget::turn_on_pressed_keys()
     }
 }
 
+void MainWidget::set_octave_and_ensure_note_change(int octave)
+{
+    turn_off_pressed_keys();
+    m_track_manager.set_octave(octave);
+    turn_on_pressed_keys();
+
+    m_knobs_widget->update_knobs();
+    m_keys_widget->update();
+}
+
 void MainWidget::set_octave_and_ensure_note_change(Direction direction)
 {
     turn_off_pressed_keys();

Applications/Piano/MainWidget.h

@@ -45,6 +45,7 @@ public:
     void add_actions(GUI::Menu&);
 
     void set_octave_and_ensure_note_change(Direction);
+    void set_octave_and_ensure_note_change(int);
 
 private:
     explicit MainWidget(TrackManager&);

Applications/Piano/TrackManager.cpp

@@ -85,6 +85,13 @@ void TrackManager::set_octave(Direction direction)
     }
 }
 
+void TrackManager::set_octave(int octave)
+{
+    if (octave <= octave_max && octave >= octave_min) {
+        m_octave = octave;
+    }
+}
+
 void TrackManager::add_track()
 {
     m_tracks.append(make<Track>(m_time));

Applications/Piano/TrackManager.h

@@ -51,6 +51,7 @@ public:
     void set_should_loop(bool b) { m_should_loop = b; }
     void set_note_current_octave(int note, Switch);
     void set_octave(Direction);
+    void set_octave(int octave);
     void add_track();
     void next_track();