LibGUI: Add ScreenRectChangeEvent and deliver it to windows and widgets

Having to rely on GUI::Desktop's on_rect_change is quite limiting and a
bit awkward (continuing to use it would mean having to setup the
callback in every application using a webview) - we need a better way of
letting widgets know of a screen rect change automatically.

The specific use case will be IPWV/OOPWV which need to keep track of the
screen rect and notify the WebContent service of any change (which on
its own deliberately can't interact with WindowServer at all).

It'll also be useful for notification windows and the taskbar, which
currently both rely on the GUI::Desktop callback but will now be able to
listen and react to the event themselves.

Userland/Libraries/LibGUI/Event.h

@@ -71,6 +71,7 @@ public:
         DragMove,
         Drop,
         ThemeChange,
+        ScreenRectChange,
 
         __Begin_WM_Events,
         WM_WindowRemoved,
@@ -399,6 +400,20 @@ public:
     }
 };
 
+class ScreenRectChangeEvent final : public Event {
+public:
+    explicit ScreenRectChangeEvent(const Gfx::IntRect& rect)
+        : Event(Type::ScreenRectChange)
+        , m_rect(rect)
+    {
+    }
+
+    const Gfx::IntRect& rect() const { return m_rect; }
+
+private:
+    Gfx::IntRect m_rect;
+};
+
 class FocusEvent final : public Event {
 public:
     explicit FocusEvent(Type type, FocusSource source)

Userland/Libraries/LibGUI/Forward.h

@@ -72,6 +72,7 @@ class Painter;
 class RadioButton;
 class ResizeCorner;
 class ResizeEvent;
+class ScreenRectChangeEvent;
 class ScrollBar;
 class ScrollableWidget;
 class Slider;

Userland/Libraries/LibGUI/Widget.cpp

@@ -556,6 +556,10 @@ void Widget::theme_change_event(ThemeChangeEvent&)
 {
 }
 
+void Widget::screen_rect_change_event(ScreenRectChangeEvent&)
+{
+}
+
 void Widget::update()
 {
     if (rect().is_empty())

Userland/Libraries/LibGUI/Widget.h

@@ -342,6 +342,7 @@ protected:
     virtual void drag_leave_event(Event&);
     virtual void drop_event(DropEvent&);
     virtual void theme_change_event(ThemeChangeEvent&);
+    virtual void screen_rect_change_event(ScreenRectChangeEvent&);
 
     virtual void did_begin_inspection() override;
     virtual void did_end_inspection() override;

Userland/Libraries/LibGUI/Window.cpp

@@ -507,6 +507,22 @@ void Window::handle_theme_change_event(ThemeChangeEvent& event)
     dispatch_theme_change(*m_main_widget.ptr(), dispatch_theme_change);
 }
 
+void Window::handle_screen_rect_change_event(ScreenRectChangeEvent& event)
+{
+    if (!m_main_widget)
+        return;
+    auto dispatch_screen_rect_change = [&](auto& widget, auto recursive) {
+        widget.dispatch_event(event, this);
+        widget.for_each_child_widget([&](auto& widget) -> IterationDecision {
+            widget.dispatch_event(event, this);
+            recursive(widget, recursive);
+            return IterationDecision::Continue;
+        });
+    };
+    dispatch_screen_rect_change(*m_main_widget.ptr(), dispatch_screen_rect_change);
+    screen_rect_change_event(event);
+}
+
 void Window::handle_drag_move_event(DragEvent& event)
 {
     if (!m_main_widget)
@@ -574,6 +590,9 @@ void Window::event(Core::Event& event)
     if (event.type() == Event::ThemeChange)
         return handle_theme_change_event(static_cast<ThemeChangeEvent&>(event));
 
+    if (event.type() == Event::ScreenRectChange)
+        return handle_screen_rect_change_event(static_cast<ScreenRectChangeEvent&>(event));
+
     Core::Object::event(event);
 }
 
@@ -799,6 +818,10 @@ void Window::wm_event(WMEvent&)
 {
 }
 
+void Window::screen_rect_change_event(ScreenRectChangeEvent&)
+{
+}
+
 void Window::set_icon(const Gfx::Bitmap* icon)
 {
     if (m_icon == icon)

Userland/Libraries/LibGUI/Window.h

@@ -216,6 +216,7 @@ public:
 protected:
     Window(Core::Object* parent = nullptr);
     virtual void wm_event(WMEvent&);
+    virtual void screen_rect_change_event(ScreenRectChangeEvent&);
 
 private:
     void update_cursor();
@@ -230,6 +231,7 @@ private:
     void handle_became_active_or_inactive_event(Core::Event&);
     void handle_close_request();
     void handle_theme_change_event(ThemeChangeEvent&);
+    void handle_screen_rect_change_event(ScreenRectChangeEvent&);
     void handle_drag_move_event(DragEvent&);
     void handle_left_event();
 

Userland/Libraries/LibGUI/WindowServerConnection.cpp

@@ -297,6 +297,9 @@ void WindowServerConnection::handle(const Messages::WindowClient::WM_WindowRemov
 void WindowServerConnection::handle(const Messages::WindowClient::ScreenRectChanged& message)
 {
     Desktop::the().did_receive_screen_rect({}, message.rect());
+    Window::for_each_window({}, [message](auto& window) {
+        Core::EventLoop::current().post_event(window, make<ScreenRectChangeEvent>(message.rect()));
+    });
 }
 
 void WindowServerConnection::handle(const Messages::WindowClient::AsyncSetWallpaperFinished&)