LibWeb: Move scroll state from Layout::BlockContainer to Layout::Box

Let's allow any box to be scrollable, not just block containers.

Userland/Libraries/LibWeb/DOM/Element.cpp

@@ -826,14 +826,14 @@ double Element::scroll_top() const
         return window->scroll_y();
 
     // 8. If the element does not have any associated box, return zero and terminate these steps.
-    if (!layout_node() || !is<Layout::BlockContainer>(layout_node()))
+    if (!layout_node() || !is<Layout::Box>(layout_node()))
         return 0.0;
 
-    auto const* block_container = static_cast<Layout::BlockContainer const*>(layout_node());
+    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 block_container->scroll_offset().y().value();
+    return box->scroll_offset().y().value();
 }
 
 double Element::scroll_left() const
@@ -868,14 +868,14 @@ double Element::scroll_left() const
         return window->scroll_x();
 
     // 8. If the element does not have any associated box, return zero and terminate these steps.
-    if (!layout_node() || !is<Layout::BlockContainer>(layout_node()))
+    if (!layout_node() || !is<Layout::Box>(layout_node()))
         return 0.0;
 
-    auto const* block_container = static_cast<Layout::BlockContainer const*>(layout_node());
+    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 block_container->scroll_offset().x().value();
+    return box->scroll_offset().x().value();
 }
 
 // https://drafts.csswg.org/cssom-view/#dom-element-scrollleft
@@ -927,20 +927,20 @@ void Element::set_scroll_left(double x)
     }
 
     // 10. If the element does not have any associated box, the element has no associated scrolling box, or the element has no overflow, terminate these steps.
-    if (!layout_node() || !is<Layout::BlockContainer>(layout_node()))
+    if (!layout_node() || !is<Layout::Box>(layout_node()))
         return;
 
-    auto* block_container = static_cast<Layout::BlockContainer*>(layout_node());
+    auto* box = static_cast<Layout::Box*>(layout_node());
-    if (!block_container->is_scrollable())
+    if (!box->is_scrollable())
         return;
 
     // FIXME: or the element has no overflow.
 
     // 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 = block_container->scroll_offset();
+    auto scroll_offset = box->scroll_offset();
     scroll_offset.set_x(static_cast<float>(x));
-    block_container->set_scroll_offset(scroll_offset);
+    box->set_scroll_offset(scroll_offset);
 }
 
 void Element::set_scroll_top(double y)
@@ -991,20 +991,20 @@ void Element::set_scroll_top(double y)
     }
 
     // 10. If the element does not have any associated box, the element has no associated scrolling box, or the element has no overflow, terminate these steps.
-    if (!layout_node() || !is<Layout::BlockContainer>(layout_node()))
+    if (!layout_node() || !is<Layout::Box>(layout_node()))
         return;
 
-    auto* block_container = static_cast<Layout::BlockContainer*>(layout_node());
+    auto* box = static_cast<Layout::Box*>(layout_node());
-    if (!block_container->is_scrollable())
+    if (!box->is_scrollable())
         return;
 
     // FIXME: or the element has no overflow.
 
     // 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 = block_container->scroll_offset();
+    auto scroll_offset = box->scroll_offset();
     scroll_offset.set_y(static_cast<float>(y));
-    block_container->set_scroll_offset(scroll_offset);
+    box->set_scroll_offset(scroll_offset);
 }
 
 int Element::scroll_width() const

Userland/Libraries/LibWeb/Layout/BlockContainer.cpp

@@ -21,21 +21,6 @@ BlockContainer::BlockContainer(DOM::Document& document, DOM::Node* node, CSS::Co
 
 BlockContainer::~BlockContainer() = default;
 
-bool BlockContainer::is_scrollable() const
-{
-    // FIXME: Support horizontal scroll as well (overflow-x)
-    return computed_values().overflow_y() == CSS::Overflow::Scroll;
-}
-
-void BlockContainer::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)
-        return;
-    m_scroll_offset = offset;
-    set_needs_display();
-}
-
 Painting::PaintableWithLines const* BlockContainer::paint_box() const
 {
     return static_cast<Painting::PaintableWithLines const*>(Box::paint_box());

Userland/Libraries/LibWeb/Layout/BlockContainer.h

@@ -20,18 +20,12 @@ public:
     BlockContainer(DOM::Document&, DOM::Node*, CSS::ComputedValues);
     virtual ~BlockContainer() override;
 
-    bool is_scrollable() const;
-    CSSPixelPoint scroll_offset() const { return m_scroll_offset; }
-    void set_scroll_offset(CSSPixelPoint);
-
     Painting::PaintableWithLines const* paint_box() const;
 
     virtual JS::GCPtr<Painting::Paintable> create_paintable() const override;
 
 private:
     virtual bool is_block_container() const final { return true; }
-
-    CSSPixelPoint m_scroll_offset;
 };
 
 template<>

Userland/Libraries/LibWeb/Layout/Box.cpp

@@ -29,6 +29,21 @@ Box::~Box()
 {
 }
 
+bool Box::is_scrollable() const
+{
+    // FIXME: Support horizontal scroll as well (overflow-x)
+    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 || m_scroll_offset == offset)
+        return;
+    m_scroll_offset = offset;
+    set_needs_display();
+}
+
 void Box::set_needs_display()
 {
     if (paint_box())

Userland/Libraries/LibWeb/Layout/Box.h

@@ -41,12 +41,18 @@ public:
 
     virtual JS::GCPtr<Painting::Paintable> create_paintable() const override;
 
+    bool is_scrollable() const;
+    CSSPixelPoint scroll_offset() const { return m_scroll_offset; }
+    void set_scroll_offset(CSSPixelPoint);
+
 protected:
     Box(DOM::Document&, DOM::Node*, NonnullRefPtr<CSS::StyleProperties>);
     Box(DOM::Document&, DOM::Node*, CSS::ComputedValues);
 
 private:
     virtual bool is_box() const final { return true; }
+
+    CSSPixelPoint m_scroll_offset;
 };
 
 template<>

Userland/Libraries/LibWeb/Painting/Paintable.cpp

@@ -36,16 +36,13 @@ Paintable::DispatchEventOfSameName Paintable::handle_mousemove(Badge<EventHandle
 bool Paintable::handle_mousewheel(Badge<EventHandler>, CSSPixelPoint, unsigned, unsigned, int wheel_delta_x, int wheel_delta_y)
 {
     if (auto* containing_block = this->containing_block()) {
-        if (!containing_block->is_block_container())
+        if (!containing_block->is_scrollable())
             return false;
-        auto* scroll_container = static_cast<Layout::BlockContainer const*>(containing_block);
+        auto new_offset = containing_block->scroll_offset();
-        if (!scroll_container->is_scrollable())
-            return false;
-        auto new_offset = scroll_container->scroll_offset();
         new_offset.translate_by(wheel_delta_x, wheel_delta_y);
         // FIXME: This const_cast is gross.
         // FIXME: Scroll offset shouldn't live in the layout tree.
-        const_cast<Layout::BlockContainer*>(scroll_container)->set_scroll_offset(new_offset);
+        const_cast<Layout::Box*>(containing_block)->set_scroll_offset(new_offset);
         return true;
     }