Piano: Highlight pressed key in roll widget

Author: https://github.com/petelliott
Commit: 01bff0141e
Pull-request: https://github.com/SerenityOS/serenity/pull/3746

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);
         }