Add a simple close button ("X") to windows.

Clicking the button generates a WindowCloseRequest event which the client app
then has to deal with. The default behavior for GWindow is to close() itself.

I also added a flag, GWindow::should_exit_event_loop_on_close() which does
what it sounds like it does.

This patch exposed some bugs in GWindow and GWidget teardown.

LibGUI/GEvent.h

@@ -24,6 +24,7 @@ public:
         WindowBecameActive,
         FocusIn,
         FocusOut,
+        WindowCloseRequest,
     };
 
     GEvent() { }

LibGUI/GEventLoop.cpp

@@ -35,6 +35,12 @@ GEventLoop& GEventLoop::main()
     return *s_mainGEventLoop;
 }
 
+void GEventLoop::exit(int code)
+{
+    m_exit_requested = true;
+    m_exit_code = code;
+}
+
 int GEventLoop::exec()
 {
     m_event_fd = open("/dev/gui_events", O_RDONLY | O_NONBLOCK | O_CLOEXEC);
@@ -45,6 +51,8 @@ int GEventLoop::exec()
 
     m_running = true;
     for (;;) {
+        if (m_exit_requested)
+            return m_exit_code;
         if (m_queued_events.is_empty())
             wait_for_event();
         Vector<QueuedEvent> events = move(m_queued_events);
@@ -69,6 +77,7 @@ int GEventLoop::exec()
             }
         }
     }
+    ASSERT_NOT_REACHED();
 }
 
 void GEventLoop::post_event(GObject* receiver, OwnPtr<GEvent>&& event)
@@ -95,6 +104,11 @@ void GEventLoop::handle_window_activation_event(const GUI_Event& event, GWindow&
     post_event(&window, make<GEvent>(event.type == GUI_Event::Type::WindowActivated ? GEvent::WindowBecameActive : GEvent::WindowBecameInactive));
 }
 
+void GEventLoop::handle_window_close_request_event(const GUI_Event&, GWindow& window)
+{
+    post_event(&window, make<GEvent>(GEvent::WindowCloseRequest));
+}
+
 void GEventLoop::handle_key_event(const GUI_Event& event, GWindow& window)
 {
 #ifdef GEVENTLOOP_DEBUG
@@ -192,6 +206,9 @@ void GEventLoop::wait_for_event()
         case GUI_Event::Type::WindowDeactivated:
             handle_window_activation_event(event, *window);
             break;
+        case GUI_Event::Type::WindowCloseRequest:
+            handle_window_close_request_event(event, *window);
+            break;
         case GUI_Event::Type::KeyDown:
         case GUI_Event::Type::KeyUp:
             handle_key_event(event, *window);

LibGUI/GEventLoop.h

@@ -27,12 +27,15 @@ public:
     int register_timer(GObject&, int milliseconds, bool should_reload);
     bool unregister_timer(int timer_id);
 
+    void exit(int);
+
 private:
     void wait_for_event();
     void handle_paint_event(const GUI_Event&, GWindow&);
     void handle_mouse_event(const GUI_Event&, GWindow&);
     void handle_key_event(const GUI_Event&, GWindow&);
     void handle_window_activation_event(const GUI_Event&, GWindow&);
+    void handle_window_close_request_event(const GUI_Event&, GWindow&);
 
     void get_next_timer_expiration(timeval&);
 
@@ -44,6 +47,8 @@ private:
 
     int m_event_fd { -1 };
     bool m_running { false };
+    bool m_exit_requested { false };
+    int m_exit_code { 0 };
 
     int m_next_timer_id { 1 };
 

LibGUI/GObject.cpp

@@ -12,6 +12,7 @@ GObject::GObject(GObject* parent)
 
 GObject::~GObject()
 {
+    stop_timer();
     if (m_parent)
         m_parent->remove_child(*this);
     auto children_to_delete = move(m_children);

LibGUI/GWindow.cpp

@@ -35,11 +35,17 @@ GWindow::GWindow(GObject* parent)
 
 GWindow::~GWindow()
 {
+    if (m_main_widget)
+        delete m_main_widget;
     hide();
 }
 
 void GWindow::close()
 {
+    // FIXME: If we exit the event loop, we're never gonna deal with the delete_later request!
+    //        This will become relevant once we support nested event loops.
+    if (should_exit_app_on_close())
+        GEventLoop::main().exit(0);
     delete_later();
 }
 
@@ -160,6 +166,11 @@ void GWindow::event(GEvent& event)
         return;
     }
 
+    if (event.type() == GEvent::WindowCloseRequest) {
+        close();
+        return;
+    }
+
     GObject::event(event);
 }
 

LibGUI/GWindow.h

@@ -53,6 +53,9 @@ public:
     GWidget* global_cursor_tracking_widget() { return m_global_cursor_tracking_widget.ptr(); }
     const GWidget* global_cursor_tracking_widget() const { return m_global_cursor_tracking_widget.ptr(); }
 
+    bool should_exit_app_on_close() const { return m_should_exit_app_on_close; }
+    void set_should_exit_app_on_close(bool b) { m_should_exit_app_on_close = b; }
+
 private:
     RetainPtr<GraphicsBitmap> m_backing;
     int m_window_id { 0 };
@@ -62,5 +65,6 @@ private:
     WeakPtr<GWidget> m_global_cursor_tracking_widget;
     Rect m_rect_when_windowless;
     String m_title_when_windowless;
+    bool m_should_exit_app_on_close { false };
 };