Added body portal class.

Author: 5cript

nui/include/nui/frontend/utility/body_portal.hpp

@@ -0,0 +1,44 @@
+#pragma once
+
+#include <nui/frontend/element_renderer.hpp>
+#include <nui/frontend/dom/element.hpp>
+
+#include <memory>
+
+namespace Nui
+{
+    /**
+     * @brief RAII wrapper that renders an ElementRenderer into a detached DOM
+     * element and appends it directly to document.body, bypassing any CSS
+     * transform / filter / perspective containment on ancestor elements in the
+     * Nui component tree.  Useful for overlays (menus, tooltips, modals) that
+     * rely on viewport-relative positioning (position:fixed).
+     *
+     * The element is removed from the DOM when the BodyPortal is destroyed.
+     * BodyPortal is non-copyable but move-constructible.
+     */
+    class BodyPortal
+    {
+      public:
+        explicit BodyPortal(Nui::ElementRenderer renderer)
+            : element_{Dom::Element::makeElement(HtmlElement{"div", &RegularHtmlElementBridge})}
+        {
+            element_->replaceElement(std::move(renderer));
+            Nui::val::global("document")["body"].call<void>("appendChild", element_->val());
+        }
+
+        BodyPortal(BodyPortal const&) = delete;
+        BodyPortal& operator=(BodyPortal const&) = delete;
+        BodyPortal(BodyPortal&&) = default;
+        BodyPortal& operator=(BodyPortal&&) = default;
+
+        ~BodyPortal()
+        {
+            if (element_)
+                element_->val().call<void>("remove");
+        }
+
+      private:
+        std::shared_ptr<Dom::Element> element_;
+    };
+}