LibWeb: Move scroll_offset() from Layout::Box to PaintableBox

Nodes in layout tree should not be aware of scroll state.

Userland/Libraries/LibWeb/DOM/Element.cpp

@@ -943,11 +943,9 @@ double Element::scroll_top() const
     if (!layout_node() || !is<Layout::Box>(layout_node()))
         return 0.0;
 
-    auto const* box = static_cast<Layout::Box const*>(layout_node());
-
     // 9. Return the y-coordinate of the scrolling area at the alignment point with the top of the padding edge of the element.
     // FIXME: Is this correct?
-    return box->scroll_offset().y().to_double();
+    return paintable_box()->scroll_offset().y().to_double();
 }
 
 double Element::scroll_left() const
@@ -985,11 +983,9 @@ double Element::scroll_left() const
     if (!layout_node() || !is<Layout::Box>(layout_node()))
         return 0.0;
 
-    auto const* box = static_cast<Layout::Box const*>(layout_node());
-
     // 9. Return the x-coordinate of the scrolling area at the alignment point with the left of the padding edge of the element.
     // FIXME: Is this correct?
-    return box->scroll_offset().x().to_double();
+    return paintable_box()->scroll_offset().x().to_double();
 }
 
 // https://drafts.csswg.org/cssom-view/#dom-element-scrollleft
@@ -1056,7 +1052,7 @@ void Element::set_scroll_left(double x)
 
     // 11. Scroll the element to x,scrollTop, with the scroll behavior being "auto".
     // FIXME: Implement this in terms of calling "scroll the element".
-    auto scroll_offset = box->scroll_offset();
+    auto scroll_offset = paintable_box()->scroll_offset();
     scroll_offset.set_x(static_cast<float>(x));
     box->set_scroll_offset(scroll_offset);
 }
@@ -1124,7 +1120,7 @@ void Element::set_scroll_top(double y)
 
     // 11. Scroll the element to scrollLeft,y, with the scroll behavior being "auto".
     // FIXME: Implement this in terms of calling "scroll the element".
-    auto scroll_offset = box->scroll_offset();
+    auto scroll_offset = paintable_box()->scroll_offset();
     scroll_offset.set_y(static_cast<float>(y));
     box->set_scroll_offset(scroll_offset);
 }

Userland/Libraries/LibWeb/Layout/Box.cpp

@@ -61,23 +61,10 @@ 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 || scroll_offset() == offset)
+    if (offset.y() < 0 || paintable_box()->scroll_offset() == offset)
         return;
 
     if (is_generated_for_before_pseudo_element()) {

Userland/Libraries/LibWeb/Layout/Box.h

@@ -54,7 +54,6 @@ public:
     bool is_scroll_container() const;
 
     bool is_scrollable() const;
-    CSSPixelPoint scroll_offset() const;
     void set_scroll_offset(CSSPixelPoint);
 
 protected:

Userland/Libraries/LibWeb/Painting/PaintableBox.cpp

@@ -57,6 +57,20 @@ PaintableWithLines::~PaintableWithLines()
 {
 }
 
+CSSPixelPoint PaintableBox::scroll_offset() const
+{
+    auto const& node = layout_node();
+    if (node.is_generated_for_before_pseudo_element())
+        return node.pseudo_element_generator()->scroll_offset(DOM::Element::ScrollOffsetFor::PseudoBefore);
+    if (node.is_generated_for_after_pseudo_element())
+        return node.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 PaintableBox::scroll_by(int delta_x, int delta_y)
 {
     auto scrollable_overflow_rect = this->scrollable_overflow_rect();
@@ -64,7 +78,7 @@ void PaintableBox::scroll_by(int delta_x, int delta_y)
         return;
     auto max_x_offset = scrollable_overflow_rect->width() - content_size().width();
     auto max_y_offset = scrollable_overflow_rect->height() - content_size().height();
-    auto current_offset = layout_box().scroll_offset();
+    auto current_offset = scroll_offset();
     auto new_offset_x = clamp(current_offset.x() + delta_x, 0, max_x_offset);
     auto new_offset_y = clamp(current_offset.y() + delta_y, 0, max_y_offset);
     layout_box().set_scroll_offset({ new_offset_x, new_offset_y });
@@ -610,7 +624,7 @@ void PaintableWithLines::paint(PaintContext& context, PaintPhase phase) const
         // FIXME: Handle overflow-x and overflow-y being different values.
         auto clip_box = context.rounded_device_rect(absolute_padding_box_rect());
         context.painter().add_clip_rect(clip_box.to_type<int>());
-        auto scroll_offset = context.rounded_device_point(static_cast<Layout::BlockContainer const&>(layout_box()).scroll_offset());
+        auto scroll_offset = context.rounded_device_point(this->scroll_offset());
         context.painter().translate(-scroll_offset.to_type<int>());
 
         auto border_radii = normalized_border_radii_data(ShrinkRadiiForBorders::Yes);

Userland/Libraries/LibWeb/Painting/PaintableBox.h

@@ -38,6 +38,7 @@ public:
     CSSPixelRect absolute_rect() const;
     CSSPixelPoint effective_offset() const;
 
+    CSSPixelPoint scroll_offset() const;
     void scroll_by(int delta_x, int delta_y);
 
     void set_offset(CSSPixelPoint);

Userland/Libraries/LibWeb/Painting/StackingContext.cpp

@@ -29,7 +29,7 @@ static void paint_node(Layout::Node const& layout_node, PaintContext& context, P
     if (auto const* paintable = layout_node.paintable()) {
         if (paintable->containing_block() && paintable->containing_block()->is_scrollable()) {
             Gfx::PainterStateSaver saver(context.painter());
-            auto scroll_offset = -paintable->containing_block()->scroll_offset();
+            auto scroll_offset = -paintable->containing_block()->paintable_box()->scroll_offset();
             context.painter().translate({ context.enclosing_device_pixels(scroll_offset.x()), context.enclosing_device_pixels(scroll_offset.y()) });
             paintable->paint(context, phase);
         } else {