LibWeb: Move scroll offset state from layout tree to dom tree

Scroll offset state should not be reset by layout tree rebuilt.

Userland/Libraries/LibWeb/DOM/Element.h

@@ -314,6 +314,14 @@ public:
     void unregister_intersection_observer(Badge<IntersectionObserver::IntersectionObserver>, JS::NonnullGCPtr<IntersectionObserver::IntersectionObserver>);
     IntersectionObserver::IntersectionObserverRegistration& get_intersection_observer_registration(Badge<DOM::Document>, IntersectionObserver::IntersectionObserver const&);
 
+    enum class ScrollOffsetFor {
+        Self,
+        PseudoBefore,
+        PseudoAfter
+    };
+    CSSPixelPoint scroll_offset(ScrollOffsetFor type) const { return m_scroll_offset[to_underlying(type)]; }
+    void set_scroll_offset(ScrollOffsetFor type, CSSPixelPoint offset) { m_scroll_offset[to_underlying(type)] = offset; }
+
 protected:
     Element(Document&, DOM::QualifiedName);
     virtual JS::ThrowCompletionOr<void> initialize(JS::Realm&) override;
@@ -367,6 +375,8 @@ private:
     // https://www.w3.org/TR/intersection-observer/#dom-element-registeredintersectionobservers-slot
     // Element objects have an internal [[RegisteredIntersectionObservers]] slot, which is initialized to an empty list.
     Vector<IntersectionObserver::IntersectionObserverRegistration> m_registered_intersection_observers;
+
+    Array<CSSPixelPoint, 3> m_scroll_offset;
 };
 
 template<>

Userland/Libraries/LibWeb/Layout/Box.cpp

@@ -61,12 +61,35 @@ bool Box::is_scrollable() const
     return computed_values().overflow_y() == CSS::Overflow::Scroll;
 }
 
+CSSPixelPoint Box::scroll_offset() const
+{
+    if (is_generated_for_before_pseudo_element())
+        return pseudo_element_generator()->scroll_offset(DOM::Element::ScrollOffsetFor::PseudoBefore);
+    if (is_generated_for_after_pseudo_element())
+        return pseudo_element_generator()->scroll_offset(DOM::Element::ScrollOffsetFor::PseudoAfter);
+
+    if (!is<DOM::Element>(*dom_node()))
+        return {};
+
+    return static_cast<DOM::Element const*>(dom_node())->scroll_offset(DOM::Element::ScrollOffsetFor::Self);
+}
+
 void Box::set_scroll_offset(CSSPixelPoint offset)
 {
     // FIXME: If there is horizontal and vertical scroll ignore only part of the new offset
-    if (offset.y() < 0 || m_scroll_offset == offset)
+    if (offset.y() < 0 || scroll_offset() == offset)
         return;
-    m_scroll_offset = offset;
+
+    if (is_generated_for_before_pseudo_element()) {
+        pseudo_element_generator()->set_scroll_offset(DOM::Element::ScrollOffsetFor::PseudoBefore, offset);
+    } else if (is_generated_for_after_pseudo_element()) {
+        pseudo_element_generator()->set_scroll_offset(DOM::Element::ScrollOffsetFor::PseudoAfter, offset);
+    } else if (is<DOM::Element>(*dom_node())) {
+        static_cast<DOM::Element*>(dom_node())->set_scroll_offset(DOM::Element::ScrollOffsetFor::Self, offset);
+    } else {
+        return;
+    }
+
     set_needs_display();
 }
 

Userland/Libraries/LibWeb/Layout/Box.h

@@ -54,7 +54,7 @@ public:
     bool is_scroll_container() const;
 
     bool is_scrollable() const;
-    CSSPixelPoint scroll_offset() const { return m_scroll_offset; }
+    CSSPixelPoint scroll_offset() const;
     void set_scroll_offset(CSSPixelPoint);
 
 protected:
@@ -64,8 +64,6 @@ protected:
 private:
     virtual bool is_box() const final { return true; }
 
-    CSSPixelPoint m_scroll_offset;
-
     Optional<CSSPixels> m_natural_width;
     Optional<CSSPixels> m_natural_height;
     Optional<float> m_natural_aspect_ratio;