LibGUI: Add GUI::Application::active_window()

Instead of each window having a bool flag that says whether that window
is currently active, have a pointer to the active window on the app
object instead.

Libraries/LibGUI/Application.cpp

@@ -235,4 +235,16 @@ void Application::tooltip_hide_timer_did_fire()
         m_tooltip_window->hide();
 }
 
+void Application::window_did_become_active(Badge<Window>, Window& window)
+{
+    m_active_window = window.make_weak_ptr<Window>();
+}
+
+void Application::window_did_become_inactive(Badge<Window>, Window& window)
+{
+    if (m_active_window.ptr() != &window)
+        return;
+    m_active_window = nullptr;
+}
+
 }

Libraries/LibGUI/Application.h

@@ -29,6 +29,7 @@
 #include <AK/HashMap.h>
 #include <AK/OwnPtr.h>
 #include <AK/String.h>
+#include <AK/WeakPtr.h>
 #include <LibCore/Object.h>
 #include <LibGUI/Forward.h>
 #include <LibGUI/Shortcut.h>
@@ -76,6 +77,12 @@ public:
 
     Core::EventLoop& event_loop() { return *m_event_loop; }
 
+    Window* active_window() { return m_active_window; }
+    const Window* active_window() const { return m_active_window; }
+
+    void window_did_become_active(Badge<Window>, Window&);
+    void window_did_become_inactive(Badge<Window>, Window&);
+
 private:
     Application(int argc, char** argv);
 
@@ -92,6 +99,7 @@ private:
     RefPtr<Core::Timer> m_tooltip_hide_timer;
     RefPtr<TooltipWindow> m_tooltip_window;
     RefPtr<Widget> m_tooltip_source_widget;
+    WeakPtr<Window> m_active_window;
     bool m_quit_when_last_window_deleted { true };
     bool m_focus_debugging_enabled { false };
     String m_invoked_as;

Libraries/LibGUI/Window.cpp

@@ -405,7 +405,10 @@ void Window::handle_input_entered_or_left_event(Core::Event& event)
 
 void Window::handle_became_active_or_inactive_event(Core::Event& event)
 {
-    m_is_active = event.type() == Event::WindowBecameActive;
+    if (event.type() == Event::WindowBecameActive)
+        Application::the()->window_did_become_active({}, *this);
+    else
+        Application::the()->window_did_become_inactive({}, *this);
     if (m_main_widget)
         m_main_widget->dispatch_event(event, this);
     if (m_focused_widget)
@@ -941,4 +944,10 @@ void Window::did_disable_focused_widget(Badge<Widget>)
     focus_a_widget_if_possible(FocusSource::Mouse);
 }
 
+bool Window::is_active() const
+{
+    ASSERT(Application::the());
+    return this == Application::the()->active_window();
+}
+
 }

Libraries/LibGUI/Window.h

@@ -113,7 +113,7 @@ public:
     virtual void event(Core::Event&) override;
 
     bool is_visible() const;
-    bool is_active() const { return m_is_active; }
+    bool is_active() const;
     bool is_active_input() const { return m_is_active_input; }
 
     bool is_accessory() const { return m_accessory; }
@@ -247,7 +247,6 @@ private:
     WindowType m_window_type { WindowType::Normal };
     Gfx::StandardCursor m_cursor { Gfx::StandardCursor::None };
     Gfx::StandardCursor m_effective_cursor { Gfx::StandardCursor::None };
-    bool m_is_active { false };
     bool m_is_active_input { false };
     bool m_has_alpha_channel { false };
     bool m_double_buffering_enabled { true };