From 268492413afbf17e4e198e73549ace9f090cb953 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Fri, 14 Jul 2023 10:02:19 +0200
Subject: [PATCH] LibWeb: Add Paintable::stacking_context_rooted_here()

This is a convenience helper that lets you get the stacking context
rooted at a given paintable, without checking that the paintable is a
box first.
---
 Userland/Libraries/LibWeb/Painting/Paintable.cpp       | 10 +++++++++-
 Userland/Libraries/LibWeb/Painting/Paintable.h         |  2 ++
 Userland/Libraries/LibWeb/Painting/StackingContext.cpp |  2 +-
 3 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/Userland/Libraries/LibWeb/Painting/Paintable.cpp b/Userland/Libraries/LibWeb/Painting/Paintable.cpp
index 24839e0bba..3abbe3a304 100644
--- a/Userland/Libraries/LibWeb/Painting/Paintable.cpp
+++ b/Userland/Libraries/LibWeb/Painting/Paintable.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2022-2023, Andreas Kling <kling@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -7,6 +7,7 @@
 #include <LibWeb/DOM/Document.h>
 #include <LibWeb/Layout/BlockContainer.h>
 #include <LibWeb/Painting/Paintable.h>
+#include <LibWeb/Painting/PaintableBox.h>
 
 namespace Web::Painting {
 
@@ -86,4 +87,11 @@ Paintable const* Paintable::previous_sibling() const
     return layout_node ? layout_node->paintable() : nullptr;
 }
 
+StackingContext const* Paintable::stacking_context_rooted_here() const
+{
+    if (!layout_node().is_box())
+        return nullptr;
+    return static_cast<PaintableBox const&>(*this).stacking_context();
+}
+
 }
diff --git a/Userland/Libraries/LibWeb/Painting/Paintable.h b/Userland/Libraries/LibWeb/Painting/Paintable.h
index 4b6c57f19b..8dd79305a5 100644
--- a/Userland/Libraries/LibWeb/Painting/Paintable.h
+++ b/Userland/Libraries/LibWeb/Painting/Paintable.h
@@ -134,6 +134,8 @@ public:
     template<typename T>
     bool fast_is() const = delete;
 
+    StackingContext const* stacking_context_rooted_here() const;
+
 protected:
     explicit Paintable(Layout::Node const& layout_node)
         : m_layout_node(layout_node)
diff --git a/Userland/Libraries/LibWeb/Painting/StackingContext.cpp b/Userland/Libraries/LibWeb/Painting/StackingContext.cpp
index b591195c09..245c593721 100644
--- a/Userland/Libraries/LibWeb/Painting/StackingContext.cpp
+++ b/Userland/Libraries/LibWeb/Painting/StackingContext.cpp
@@ -444,7 +444,7 @@ Gfx::FloatPoint StackingContext::compute_transform_origin() const
 template<typename U, typename Callback>
 static TraversalDecision for_each_in_inclusive_subtree_of_type_within_same_stacking_context_in_reverse(Paintable const& paintable, Callback callback)
 {
-    if (is<PaintableBox>(paintable) && static_cast<PaintableBox const&>(paintable).stacking_context()) {
+    if (paintable.stacking_context_rooted_here()) {
         // Note: Include the stacking context (so we can hit test it), but don't recurse into it.
         if (auto decision = callback(static_cast<U const&>(paintable)); decision != TraversalDecision::Continue)
             return decision;