LibGUI: Implement enter/leave events (with WindowServer support.)

Windows now learn when the mouse cursor leaves or enters them.
Use this to implement GWidget::{enter,leave}_event() and use that
to implement the CoolBar button effect. :^)

LibGUI/GButton.cpp

@@ -89,3 +89,14 @@ void GButton::mouseup_event(GMouseEvent& event)
     GWidget::mouseup_event(event);
 }
 
+void GButton::enter_event(GEvent&)
+{
+    m_hovered = true;
+    update();
+}
+
+void GButton::leave_event(GEvent&)
+{
+    m_hovered = false;
+    update();
+}

LibGUI/GButton.h

@@ -28,6 +28,8 @@ private:
     virtual void mousedown_event(GMouseEvent&) override;
     virtual void mouseup_event(GMouseEvent&) override;
     virtual void mousemove_event(GMouseEvent&) override;
+    virtual void enter_event(GEvent&) override;
+    virtual void leave_event(GEvent&) override;
 
     virtual const char* class_name() const override { return "GButton"; }
 

LibGUI/GEvent.h

@@ -17,10 +17,14 @@ public:
         MouseMove,
         MouseDown,
         MouseUp,
+        Enter,
+        Leave,
         KeyDown,
         KeyUp,
         Timer,
         DeferredDestroy,
+        WindowEntered,
+        WindowLeft,
         WindowBecameInactive,
         WindowBecameActive,
         FocusIn,

LibGUI/GEventLoop.cpp

@@ -134,6 +134,11 @@ void GEventLoop::handle_window_close_request_event(const WSAPI_ServerMessage&, G
     post_event(&window, make<GEvent>(GEvent::WindowCloseRequest));
 }
 
+void GEventLoop::handle_window_entered_or_left_event(const WSAPI_ServerMessage& message, GWindow& window)
+{
+    post_event(&window, make<GEvent>(message.type == WSAPI_ServerMessage::Type::WindowEntered ? GEvent::WindowEntered : GEvent::WindowLeft));
+}
+
 void GEventLoop::handle_key_event(const WSAPI_ServerMessage& event, GWindow& window)
 {
 #ifdef GEVENTLOOP_DEBUG
@@ -294,6 +299,10 @@ void GEventLoop::wait_for_event()
         case WSAPI_ServerMessage::Type::KeyUp:
             handle_key_event(event, *window);
             break;
+        case WSAPI_ServerMessage::Type::WindowEntered:
+        case WSAPI_ServerMessage::Type::WindowLeft:
+            handle_window_entered_or_left_event(event, *window);
+            break;
         default:
             break;
         }

LibGUI/GEventLoop.h

@@ -48,6 +48,7 @@ private:
     void handle_window_activation_event(const WSAPI_ServerMessage&, GWindow&);
     void handle_window_close_request_event(const WSAPI_ServerMessage&, GWindow&);
     void handle_menu_event(const WSAPI_ServerMessage&);
+    void handle_window_entered_or_left_event(const WSAPI_ServerMessage&, GWindow&);
     void get_next_timer_expiration(timeval&);
 
     struct QueuedEvent {

LibGUI/GWidget.cpp

@@ -63,6 +63,10 @@ void GWidget::event(GEvent& event)
         return mousedown_event(static_cast<GMouseEvent&>(event));
     case GEvent::MouseUp:
         return mouseup_event(static_cast<GMouseEvent&>(event));
+    case GEvent::Enter:
+        return enter_event(event);
+    case GEvent::Leave:
+        return leave_event(event);
     default:
         return GObject::event(event);
     }
@@ -173,6 +177,14 @@ void GWidget::focusout_event(GEvent&)
 {
 }
 
+void GWidget::enter_event(GEvent&)
+{
+}
+
+void GWidget::leave_event(GEvent&)
+{
+}
+
 void GWidget::update()
 {
     update(rect());

LibGUI/GWidget.h

@@ -43,6 +43,8 @@ public:
     virtual void mouseup_event(GMouseEvent&);
     virtual void focusin_event(GEvent&);
     virtual void focusout_event(GEvent&);
+    virtual void enter_event(GEvent&);
+    virtual void leave_event(GEvent&);
 
     Rect relative_rect() const { return m_relative_rect; }
     Point relative_position() const { return m_relative_rect.location(); }

LibGUI/GWindow.cpp

@@ -157,6 +157,7 @@ void GWindow::event(GEvent& event)
             auto result = m_main_widget->hit_test(mouse_event.x(), mouse_event.y());
             auto local_event = make<GMouseEvent>(event.type(), Point { result.localX, result.localY }, mouse_event.buttons(), mouse_event.button());
             ASSERT(result.widget);
+            set_hovered_widget(result.widget);
             return result.widget->event(*local_event);
         }
         return;
@@ -203,6 +204,11 @@ void GWindow::event(GEvent& event)
         return;
     }
 
+    if (event.type() == GEvent::WindowLeft) {
+        set_hovered_widget(nullptr);
+        return;
+    }
+
     GObject::event(event);
 }
 
@@ -301,3 +307,17 @@ void GWindow::set_opacity(float opacity)
     m_opacity_when_windowless = opacity;
     GEventLoop::main().post_message_to_server(request);
 }
+
+void GWindow::set_hovered_widget(GWidget* widget)
+{
+    if (widget == m_hovered_widget.ptr())
+        return;
+
+    if (m_hovered_widget)
+        GEventLoop::main().post_event(m_hovered_widget.ptr(), make<GEvent>(GEvent::Leave));
+
+    m_hovered_widget = widget ? widget->make_weak_ptr() : nullptr;
+
+    if (m_hovered_widget)
+        GEventLoop::main().post_event(m_hovered_widget.ptr(), make<GEvent>(GEvent::Enter));
+}

LibGUI/GWindow.h

@@ -64,6 +64,10 @@ public:
     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; }
 
+    GWidget* hovered_widget() { return m_hovered_widget.ptr(); }
+    const GWidget* hovered_widget() const { return m_hovered_widget.ptr(); }
+    void set_hovered_widget(GWidget*);
+
 private:
     virtual const char* class_name() const override { return "GWindow"; }
 
@@ -73,6 +77,7 @@ private:
     GWidget* m_main_widget { nullptr };
     GWidget* m_focused_widget { nullptr };
     WeakPtr<GWidget> m_global_cursor_tracking_widget;
+    WeakPtr<GWidget> m_hovered_widget;
     Rect m_rect_when_windowless;
     String m_title_when_windowless;
     Vector<Rect> m_pending_paint_event_rects;