LibGUI: Add "drag enter" and "drag leave" events

These events allow widgets to react when a drag enters/leaves their
rectangle. The enter event carries position + mime type, while the
leave event has no information.

Libraries/LibGUI/Application.cpp

@@ -247,4 +247,27 @@ void Application::window_did_become_inactive(Badge<Window>, Window& window)
     m_active_window = nullptr;
 }
 
+void Application::set_drag_hovered_widget_impl(Widget* widget, const Gfx::IntPoint& position, const String& mime_type)
+{
+    if (widget == m_drag_hovered_widget)
+        return;
+
+    if (m_drag_hovered_widget) {
+        m_drag_hovered_widget->update();
+        Core::EventLoop::current().post_event(*m_drag_hovered_widget, make<Event>(Event::DragLeave));
+    }
+
+    m_drag_hovered_widget = widget;
+
+    if (m_drag_hovered_widget) {
+        m_drag_hovered_widget->update();
+        Core::EventLoop::current().post_event(*m_drag_hovered_widget, make<DragEvent>(Event::DragEnter, position, mime_type));
+    }
+}
+
+void Application::notify_drag_cancelled(Badge<WindowServerConnection>)
+{
+    set_drag_hovered_widget_impl(nullptr);
+}
+
 }

Libraries/LibGUI/Application.h

@@ -34,7 +34,7 @@
 #include <LibGUI/Forward.h>
 #include <LibGUI/Shortcut.h>
 #include <LibGUI/Widget.h>
-#include <LibGfx/Forward.h>
+#include <LibGfx/Point.h>
 
 namespace GUI {
 
@@ -83,12 +83,23 @@ public:
     void window_did_become_active(Badge<Window>, Window&);
     void window_did_become_inactive(Badge<Window>, Window&);
 
+    Widget* drag_hovered_widget() { return m_drag_hovered_widget.ptr(); }
+    const Widget* drag_hovered_widget() const { return m_drag_hovered_widget.ptr(); }
+
+    void set_drag_hovered_widget(Badge<Window>, Widget* widget, const Gfx::IntPoint& position = {}, const String& mime_type = {})
+    {
+        set_drag_hovered_widget_impl(widget, position, mime_type);
+    }
+    void notify_drag_cancelled(Badge<WindowServerConnection>);
+
 private:
     Application(int argc, char** argv);
 
     void tooltip_show_timer_did_fire();
     void tooltip_hide_timer_did_fire();
 
+    void set_drag_hovered_widget_impl(Widget*, const Gfx::IntPoint& = {}, const String& = {});
+
     OwnPtr<Core::EventLoop> m_event_loop;
     RefPtr<MenuBar> m_menubar;
     RefPtr<Gfx::PaletteImpl> m_palette;
@@ -104,6 +115,7 @@ private:
     bool m_focus_debugging_enabled { false };
     String m_invoked_as;
     Vector<String> m_args;
+    WeakPtr<Widget> m_drag_hovered_widget;
 };
 
 }

Libraries/LibGUI/Event.h

@@ -65,6 +65,8 @@ public:
         WindowCloseRequest,
         ContextMenu,
         EnabledChange,
+        DragEnter,
+        DragLeave,
         DragMove,
         Drop,
         ThemeChange,

Libraries/LibGUI/Widget.cpp

@@ -273,8 +273,12 @@ void Widget::event(Core::Event& event)
         return handle_mouseup_event(static_cast<MouseEvent&>(event));
     case Event::MouseWheel:
         return mousewheel_event(static_cast<MouseEvent&>(event));
+    case Event::DragEnter:
+        return drag_enter_event(static_cast<DragEvent&>(event));
     case Event::DragMove:
         return drag_move_event(static_cast<DragEvent&>(event));
+    case Event::DragLeave:
+        return drag_leave_event(static_cast<Event&>(event));
     case Event::Drop:
         return drop_event(static_cast<DropEvent&>(event));
     case Event::ThemeChange:
@@ -497,13 +501,24 @@ void Widget::change_event(Event&)
 
 void Widget::drag_move_event(DragEvent& event)
 {
-    dbg() << class_name() << "{" << this << "} DRAG MOVE  position: " << event.position() << ", data_type: '" << event.data_type() << "'";
+    event.ignore();
+}
+
+void Widget::drag_enter_event(DragEvent& event)
+{
+    dbgln("{} {:p} DRAG ENTER @ {}, {}", class_name(), this, event.position(), event.data_type());
+    event.ignore();
+}
+
+void Widget::drag_leave_event(Event& event)
+{
+    dbgln("{} {:p} DRAG LEAVE", class_name(), this);
     event.ignore();
 }
 
 void Widget::drop_event(DropEvent& event)
 {
-    dbg() << class_name() << "{" << this << "} DROP  position: " << event.position() << ", text: '" << event.text() << "'";
+    dbgln("{} {:p} DROP @ {}, '{}'", class_name(), this, event.position(), event.text());
     event.ignore();
 }
 

Libraries/LibGUI/Widget.h

@@ -324,7 +324,9 @@ protected:
     virtual void leave_event(Core::Event&);
     virtual void child_event(Core::ChildEvent&) override;
     virtual void change_event(Event&);
+    virtual void drag_enter_event(DragEvent&);
     virtual void drag_move_event(DragEvent&);
+    virtual void drag_leave_event(Event&);
     virtual void drop_event(DropEvent&);
     virtual void theme_change_event(ThemeChangeEvent&);
 

Libraries/LibGUI/Window.cpp

@@ -446,12 +446,14 @@ void Window::handle_drag_move_event(DragEvent& event)
     auto result = m_main_widget->hit_test(event.position());
     auto local_event = make<DragEvent>(static_cast<Event::Type>(event.type()), result.local_position, event.data_type());
     ASSERT(result.widget);
+    Application::the()->set_drag_hovered_widget({}, result.widget, result.local_position, event.data_type());
     return result.widget->dispatch_event(*local_event, this);
 }
 
 void Window::handle_left_event()
 {
     set_hovered_widget(nullptr);
+    Application::the()->set_drag_hovered_widget({}, nullptr);
 }
 
 void Window::event(Core::Event& event)

Libraries/LibGUI/WindowServerConnection.cpp

@@ -325,6 +325,7 @@ void WindowServerConnection::handle(const Messages::WindowClient::DragAccepted&)
 void WindowServerConnection::handle(const Messages::WindowClient::DragCancelled&)
 {
     DragOperation::notify_cancelled({});
+    Application::the()->notify_drag_cancelled({});
 }
 
 void WindowServerConnection::handle(const Messages::WindowClient::WindowStateChanged& message)