LibWeb: Resolve box shadow data for paintable boxes during layout

Step towards making the paintable tree independent of the layout tree.

Userland/Libraries/LibWeb/Layout/LayoutState.cpp

@@ -336,6 +336,33 @@ void LayoutState::resolve_border_radii()
     }
 }
 
+void LayoutState::resolve_box_shadow_data()
+{
+    for (auto& it : used_values_per_layout_node) {
+        auto& used_values = *it.value;
+        auto& node = const_cast<NodeWithStyle&>(used_values.node());
+        auto* paintable = node.paintable();
+        if (paintable && is<Painting::PaintableBox>(*paintable)) {
+            auto box_shadow_data = node.computed_values().box_shadow();
+            if (box_shadow_data.is_empty())
+                continue;
+            auto& paintable_box = static_cast<Painting::PaintableBox&>(*paintable);
+            Vector<Painting::ShadowData> resolved_box_shadow_data;
+            resolved_box_shadow_data.ensure_capacity(box_shadow_data.size());
+            for (auto const& layer : box_shadow_data) {
+                resolved_box_shadow_data.empend(
+                    layer.color,
+                    layer.offset_x.to_px(node),
+                    layer.offset_y.to_px(node),
+                    layer.blur_radius.to_px(node),
+                    layer.spread_distance.to_px(node),
+                    layer.placement == CSS::ShadowPlacement::Outer ? Painting::ShadowPlacement::Outer : Painting::ShadowPlacement::Inner);
+            }
+            paintable_box.set_box_shadow_data(move(resolved_box_shadow_data));
+        }
+    }
+}
+
 void LayoutState::commit(Box& root)
 {
     // Only the top-level LayoutState should ever be committed.
@@ -432,6 +459,7 @@ void LayoutState::commit(Box& root)
     }
 
     resolve_border_radii();
+    resolve_box_shadow_data();
 }
 
 void LayoutState::UsedValues::set_node(NodeWithStyle& node, UsedValues const* containing_block_used_values)

Userland/Libraries/LibWeb/Layout/LayoutState.h

@@ -187,6 +187,7 @@ struct LayoutState {
 private:
     void resolve_relative_positions(Vector<Painting::PaintableWithLines&> const&);
     void resolve_border_radii();
+    void resolve_box_shadow_data();
 };
 
 }

Userland/Libraries/LibWeb/Painting/PaintableBox.cpp

@@ -148,8 +148,7 @@ CSSPixelRect PaintableBox::compute_absolute_paint_rect() const
         if (computed_values().overflow_y() == CSS::Overflow::Visible)
             rect.unite_vertically(scrollable_overflow_rect);
     }
-    auto resolved_box_shadow_data = resolve_box_shadow_data();
+    for (auto const& shadow : box_shadow_data()) {
-    for (auto const& shadow : resolved_box_shadow_data) {
         if (shadow.placement == ShadowPlacement::Inner)
             continue;
         auto inflate = shadow.spread_distance + shadow.blur_radius;
@@ -355,30 +354,9 @@ void PaintableBox::paint_background(PaintContext& context) const
     Painting::paint_background(context, layout_box(), background_rect, background_color, computed_values().image_rendering(), background_layers, normalized_border_radii_data());
 }
 
-Vector<ShadowData> PaintableBox::resolve_box_shadow_data() const
-{
-    auto box_shadow_data = computed_values().box_shadow();
-    if (box_shadow_data.is_empty())
-        return {};
-
-    Vector<ShadowData> resolved_box_shadow_data;
-    resolved_box_shadow_data.ensure_capacity(box_shadow_data.size());
-    for (auto const& layer : box_shadow_data) {
-        resolved_box_shadow_data.empend(
-            layer.color,
-            layer.offset_x.to_px(layout_box()),
-            layer.offset_y.to_px(layout_box()),
-            layer.blur_radius.to_px(layout_box()),
-            layer.spread_distance.to_px(layout_box()),
-            layer.placement == CSS::ShadowPlacement::Outer ? ShadowPlacement::Outer : ShadowPlacement::Inner);
-    }
-
-    return resolved_box_shadow_data;
-}
-
 void PaintableBox::paint_box_shadow(PaintContext& context) const
 {
-    auto resolved_box_shadow_data = resolve_box_shadow_data();
+    auto const& resolved_box_shadow_data = box_shadow_data();
     if (resolved_box_shadow_data.is_empty())
         return;
     auto borders_data = BordersData {

Userland/Libraries/LibWeb/Painting/PaintableBox.h

@@ -191,6 +191,9 @@ public:
     BorderRadiiData const& border_radii_data() const { return m_border_radii_data; }
     void set_border_radii_data(BorderRadiiData const& border_radii_data) { m_border_radii_data = border_radii_data; }
 
+    void set_box_shadow_data(Vector<ShadowData> box_shadow_data) { m_box_shadow_data = move(box_shadow_data); }
+    Vector<ShadowData> const& box_shadow_data() const { return m_box_shadow_data; }
+
     PaintableBox const* nearest_scrollable_ancestor() const;
 
 protected:
@@ -206,8 +209,6 @@ protected:
     virtual CSSPixelRect compute_absolute_rect() const;
     virtual CSSPixelRect compute_absolute_paint_rect() const;
 
-    Vector<ShadowData> resolve_box_shadow_data() const;
-
 private:
     [[nodiscard]] virtual bool is_paintable_box() const final { return true; }
 
@@ -230,6 +231,7 @@ private:
     Optional<TableCellCoordinates> m_table_cell_coordinates;
 
     BorderRadiiData m_border_radii_data;
+    Vector<ShadowData> m_box_shadow_data;
 };
 
 class PaintableWithLines : public PaintableBox {