Taskbar: Only show the current desktop's window buttons

By tracking what virtual desktop a window is on, and what desktop is
being viewed we can show or hide the window buttons accordingly.

Userland/Services/Taskbar/TaskbarWindow.cpp

@@ -221,6 +221,7 @@ void TaskbarWindow::update_window_button(::Window& window, bool show_as_active)
     button->set_text(window.title());
     button->set_tooltip(window.title());
     button->set_checked(show_as_active);
+    button->set_visible(is_window_on_current_virtual_desktop(window));
 }
 
 ::Window* TaskbarWindow::find_window_owner(::Window& window) const
@@ -304,6 +305,7 @@ void TaskbarWindow::wm_event(GUI::WMEvent& event)
         window.set_active(changed_event.is_active());
         window.set_minimized(changed_event.is_minimized());
         window.set_progress(changed_event.progress());
+        window.set_virtual_desktop(changed_event.virtual_desktop_row(), changed_event.virtual_desktop_column());
 
         auto* window_owner = find_window_owner(window);
         if (window_owner == &window) {
@@ -336,6 +338,10 @@ void TaskbarWindow::wm_event(GUI::WMEvent& event)
             warnln("failed to spawn 'Assistant' when requested via Super+Space");
         break;
     }
+    case GUI::Event::WM_VirtualDesktopChanged: {
+        auto& changed_event = static_cast<GUI::WMVirtualDesktopChangedEvent&>(event);
+        virtual_desktop_change_event(changed_event.current_row(), changed_event.current_column());
+    }
     default:
         break;
     }
@@ -345,3 +351,19 @@ void TaskbarWindow::screen_rects_change_event(GUI::ScreenRectsChangeEvent& event
 {
     on_screen_rects_change(event.rects(), event.main_screen_index());
 }
+
+bool TaskbarWindow::is_window_on_current_virtual_desktop(::Window& window) const
+{
+    return window.virtual_desktop_row() == m_current_virtual_desktop_row && window.virtual_desktop_column() == m_current_virtual_desktop_column;
+}
+
+void TaskbarWindow::virtual_desktop_change_event(unsigned current_row, unsigned current_column)
+{
+    m_current_virtual_desktop_row = current_row;
+    m_current_virtual_desktop_column = current_column;
+
+    WindowList::the().for_each_window([&](auto& window) {
+        if (auto* button = window.button())
+            button->set_visible(is_window_on_current_virtual_desktop(window));
+    });
+}

Userland/Services/Taskbar/TaskbarWindow.h

@@ -34,6 +34,9 @@ private:
 
     void update_applet_area();
 
+    bool is_window_on_current_virtual_desktop(::Window&) const;
+    void virtual_desktop_change_event(unsigned, unsigned);
+
     NonnullRefPtr<GUI::Menu> m_start_menu;
     RefPtr<GUI::Widget> m_task_button_container;
     RefPtr<Gfx::Bitmap> m_default_icon;
@@ -43,4 +46,7 @@ private:
     RefPtr<GUI::Button> m_start_button;
 
     RefPtr<Desktop::AppFile> m_assistant_app_file;
+
+    unsigned m_current_virtual_desktop_row { 0 };
+    unsigned m_current_virtual_desktop_column { 0 };
 };

Userland/Services/Taskbar/WindowList.h

@@ -48,6 +48,14 @@ public:
     void set_modal(bool modal) { m_modal = modal; }
     bool is_modal() const { return m_modal; }
 
+    void set_virtual_desktop(unsigned row, unsigned column)
+    {
+        m_virtual_desktop_row = row;
+        m_virtual_desktop_column = column;
+    }
+    unsigned virtual_desktop_row() const { return m_virtual_desktop_row; }
+    unsigned virtual_desktop_column() const { return m_virtual_desktop_column; }
+
     void set_progress(Optional<int> progress)
     {
         if (m_progress == progress)
@@ -68,6 +76,8 @@ private:
     Gfx::IntRect m_rect;
     RefPtr<GUI::Button> m_button;
     RefPtr<Gfx::Bitmap> m_icon;
+    unsigned m_virtual_desktop_row { 0 };
+    unsigned m_virtual_desktop_column { 0 };
     bool m_active { false };
     bool m_minimized { false };
     bool m_modal { false };

Userland/Services/Taskbar/main.cpp

@@ -60,7 +60,8 @@ int main(int argc, char** argv)
     window->make_window_manager(
         WindowServer::WMEventMask::WindowStateChanges
         | WindowServer::WMEventMask::WindowRemovals
-        | WindowServer::WMEventMask::WindowIconChanges);
+        | WindowServer::WMEventMask::WindowIconChanges
+        | WindowServer::WMEventMask::VirtualDesktopChanges);
 
     return app->exec();
 }