Piano: Highlight pressed key in roll widget

Applications/Piano/KeysWidget.cpp

@@ -63,6 +63,17 @@ void KeysWidget::set_key(int key, Switch switch_key)
     m_track_manager.set_note_current_octave(key, switch_key);
 }
 
+bool KeysWidget::note_is_set(int note) const
+{
+    if (note < m_track_manager.octave_base())
+        return false;
+
+    if (note >= m_track_manager.octave_base() + note_count)
+        return false;
+
+    return m_key_on[note - m_track_manager.octave_base()] != 0;
+}
+
 int KeysWidget::key_code_to_key(int key_code) const
 {
     switch (key_code) {

Applications/Piano/KeysWidget.h

@@ -41,6 +41,7 @@ public:
     int mouse_note() const;
 
     void set_key(int key, Switch);
+    bool note_is_set(int note) const;
 
 private:
     explicit KeysWidget(TrackManager&);

Applications/Piano/MainWidget.cpp

@@ -69,6 +69,8 @@ MainWidget::MainWidget(TrackManager& track_manager)
     m_knobs_widget = m_keys_and_knobs_container->add<KnobsWidget>(track_manager, *this);
     m_knobs_widget->set_size_policy(GUI::SizePolicy::Fixed, GUI::SizePolicy::Fill);
     m_knobs_widget->set_preferred_size(350, 0);
+
+    m_roll_widget->set_keys_widget(m_keys_widget);
 }
 
 MainWidget::~MainWidget()

Applications/Piano/RollWidget.cpp

@@ -92,6 +92,8 @@ void RollWidget::paint_event(GUI::PaintEvent& event)
 
     for (int y = 0; y < notes_to_paint; ++y) {
         int y_pos = y * note_height;
+
+        int note = (note_count - note_offset - 1) - y;
         for (int x = 0; x < horizontal_notes_to_paint; ++x) {
             // This is needed to avoid rounding errors. You can't just use
             // m_note_width as the width.
@@ -105,6 +107,9 @@ void RollWidget::paint_event(GUI::PaintEvent& event)
             else
                 painter.fill_rect(rect, Color::White);
 
+            if (keys_widget() && keys_widget()->note_is_set(note))
+                painter.fill_rect(rect, note_pressed_color.with_alpha(128));
+
             painter.draw_line(rect.top_right(), rect.bottom_right(), Color::Black);
             painter.draw_line(rect.bottom_left(), rect.bottom_right(), Color::Black);
         }

Applications/Piano/RollWidget.h

@@ -27,6 +27,7 @@
 
 #pragma once
 
+#include "KeysWidget.h"
 #include "Music.h"
 #include <LibGUI/ScrollableWidget.h>
 
@@ -37,6 +38,9 @@ class RollWidget final : public GUI::ScrollableWidget {
 public:
     virtual ~RollWidget() override;
 
+    const KeysWidget* keys_widget() const { return m_keys_widget; }
+    void set_keys_widget(const KeysWidget* widget) { m_keys_widget = widget; }
+
 private:
     explicit RollWidget(TrackManager&);
 
@@ -45,6 +49,7 @@ private:
     virtual void mousewheel_event(GUI::MouseEvent&) override;
 
     TrackManager& m_track_manager;
+    const KeysWidget* m_keys_widget;
 
     int m_roll_width { 0 };
     int m_num_notes { 0 };

Libraries/LibGfx/Color.h

@@ -117,7 +117,7 @@ public:
         m_value |= value;
     }
 
-    Color with_alpha(u8 alpha)
+    Color with_alpha(u8 alpha) const
     {
         return Color((m_value & 0x00ffffff) | alpha << 24);
     }