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

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

Userland/Libraries/LibWeb/DOM/Element.cpp

@@ -1054,7 +1054,7 @@ void Element::set_scroll_left(double x)
     // FIXME: Implement this in terms of calling "scroll the element".
     auto scroll_offset = paintable_box()->scroll_offset();
     scroll_offset.set_x(static_cast<float>(x));
-    box->set_scroll_offset(scroll_offset);
+    const_cast<Painting::PaintableBox*>(paintable_box())->set_scroll_offset(scroll_offset);
 }
 
 void Element::set_scroll_top(double y)
@@ -1122,7 +1122,7 @@ void Element::set_scroll_top(double y)
     // FIXME: Implement this in terms of calling "scroll the element".
     auto scroll_offset = paintable_box()->scroll_offset();
     scroll_offset.set_y(static_cast<float>(y));
-    box->set_scroll_offset(scroll_offset);
+    const_cast<Painting::PaintableBox*>(paintable_box())->set_scroll_offset(scroll_offset);
 }
 
 // https://drafts.csswg.org/cssom-view/#dom-element-scrollwidth

Userland/Libraries/LibWeb/Layout/Box.cpp

@@ -61,25 +61,6 @@ bool Box::is_scrollable() const
     return computed_values().overflow_y() == CSS::Overflow::Scroll;
 }
 
-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 || paintable_box()->scroll_offset() == offset)
-        return;
-
-    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();
-}
-
 void Box::set_needs_display()
 {
     if (paintable_box())

Userland/Libraries/LibWeb/Layout/Box.h

@@ -54,7 +54,6 @@ public:
     bool is_scroll_container() const;
 
     bool is_scrollable() const;
-    void set_scroll_offset(CSSPixelPoint);
 
 protected:
     Box(DOM::Document&, DOM::Node*, NonnullRefPtr<CSS::StyleProperties>);

Userland/Libraries/LibWeb/Painting/PaintableBox.cpp

@@ -71,6 +71,26 @@ CSSPixelPoint PaintableBox::scroll_offset() const
     return static_cast<DOM::Element const*>(dom_node())->scroll_offset(DOM::Element::ScrollOffsetFor::Self);
 }
 
+void PaintableBox::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)
+        return;
+
+    auto& node = layout_node();
+    if (node.is_generated_for_before_pseudo_element()) {
+        node.pseudo_element_generator()->set_scroll_offset(DOM::Element::ScrollOffsetFor::PseudoBefore, offset);
+    } else if (node.is_generated_for_after_pseudo_element()) {
+        node.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;
+    }
+
+    node.set_needs_display();
+}
+
 void PaintableBox::scroll_by(int delta_x, int delta_y)
 {
     auto scrollable_overflow_rect = this->scrollable_overflow_rect();
@@ -81,7 +101,7 @@ void PaintableBox::scroll_by(int delta_x, int delta_y)
     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 });
+    set_scroll_offset({ new_offset_x, new_offset_y });
 }
 
 void PaintableBox::set_offset(CSSPixelPoint offset)

Userland/Libraries/LibWeb/Painting/PaintableBox.h

@@ -39,6 +39,7 @@ public:
     CSSPixelPoint effective_offset() const;
 
     CSSPixelPoint scroll_offset() const;
+    void set_scroll_offset(CSSPixelPoint);
     void scroll_by(int delta_x, int delta_y);
 
     void set_offset(CSSPixelPoint);