LibWeb: Move line boxes from Layout::Box to BlockContainer

Per the spec, only a BlockContainer" can have line boxes, so let's not
clutter up every Layout::Box with line boxes.

This also allows us to establish an invariant that BFC and IFC always
operate on a Layout::BlockContainer.

Note that if BlockContainer has all block-level children, its line boxes
are not used for anything. They are only used in the all inline-level
children scenario.

Userland/Libraries/LibWeb/Layout/BlockContainer.cpp

@@ -147,4 +147,17 @@ bool BlockContainer::handle_mousewheel(Badge<EventHandler>, const Gfx::IntPoint&
     return true;
 }
 
+LineBox& BlockContainer::ensure_last_line_box()
+{
+    if (m_line_boxes.is_empty())
+        return add_line_box();
+    return m_line_boxes.last();
+}
+
+LineBox& BlockContainer::add_line_box()
+{
+    m_line_boxes.append(LineBox());
+    return m_line_boxes.last();
+}
+
 }

Userland/Libraries/LibWeb/Layout/BlockContainer.h

@@ -38,6 +38,15 @@ public:
     const Gfx::FloatPoint& scroll_offset() const { return m_scroll_offset; }
     void set_scroll_offset(const Gfx::FloatPoint&);
 
+    Vector<LineBox>& line_boxes() { return m_line_boxes; }
+    const Vector<LineBox>& line_boxes() const { return m_line_boxes; }
+
+    LineBox& ensure_last_line_box();
+    LineBox& add_line_box();
+
+protected:
+    Vector<LineBox> m_line_boxes;
+
 private:
     virtual bool is_block_container() const final { return true; }
     virtual bool wants_mouse_events() const override { return false; }

Userland/Libraries/LibWeb/Layout/BlockFormattingContext.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2020-2021, Andreas Kling <kling@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -17,7 +17,7 @@
 
 namespace Web::Layout {
 
-BlockFormattingContext::BlockFormattingContext(Box& root, FormattingContext* parent)
+BlockFormattingContext::BlockFormattingContext(BlockContainer& root, FormattingContext* parent)
     : FormattingContext(root, parent)
 {
 }
@@ -46,9 +46,9 @@ void BlockFormattingContext::run(Box& box, LayoutMode layout_mode)
         compute_width(box);
 
     if (box.children_are_inline()) {
-        layout_inline_children(box, layout_mode);
+        layout_inline_children(verify_cast<BlockContainer>(box), layout_mode);
     } else {
-        layout_block_level_children(box, layout_mode);
+        layout_block_level_children(verify_cast<BlockContainer>(box), layout_mode);
     }
 
     if (layout_mode == LayoutMode::Default) {
@@ -289,7 +289,7 @@ void BlockFormattingContext::compute_width_for_block_level_replaced_element_in_n
     box.set_width(compute_width_for_replaced_element(box));
 }
 
-static float compute_auto_height_for_block_level_element(const Box& box)
+static float compute_auto_height_for_block_level_element(Box const& box)
 {
     Optional<float> top;
     Optional<float> bottom;
@@ -297,12 +297,13 @@ static float compute_auto_height_for_block_level_element(const Box& box)
     if (box.children_are_inline()) {
         // If it only has inline-level children, the height is the distance between
         // the top of the topmost line box and the bottom of the bottommost line box.
-        if (!box.line_boxes().is_empty()) {
+        auto& block_container = verify_cast<Layout::BlockContainer>(box);
-            for (auto& fragment : box.line_boxes().first().fragments()) {
+        if (!block_container.line_boxes().is_empty()) {
+            for (auto& fragment : block_container.line_boxes().first().fragments()) {
                 if (!top.has_value() || fragment.offset().y() < top.value())
                     top = fragment.offset().y();
             }
-            for (auto& fragment : box.line_boxes().last().fragments()) {
+            for (auto& fragment : block_container.line_boxes().last().fragments()) {
                 if (!bottom.has_value() || (fragment.offset().y() + fragment.height()) > bottom.value())
                     bottom = fragment.offset().y() + fragment.height();
             }
@@ -415,23 +416,23 @@ void BlockFormattingContext::compute_position(Box& box)
     }
 }
 
-void BlockFormattingContext::layout_inline_children(Box& box, LayoutMode layout_mode)
+void BlockFormattingContext::layout_inline_children(BlockContainer& block_container, LayoutMode layout_mode)
 {
-    InlineFormattingContext context(box, this);
+    InlineFormattingContext context(block_container, this);
-    context.run(box, layout_mode);
+    context.run(block_container, layout_mode);
 }
 
-void BlockFormattingContext::layout_block_level_children(Box& box, LayoutMode layout_mode)
+void BlockFormattingContext::layout_block_level_children(BlockContainer& block_container, LayoutMode layout_mode)
 {
     float content_height = 0;
     float content_width = 0;
 
-    box.for_each_child_of_type<Box>([&](auto& child_box) {
+    block_container.for_each_child_of_type<Box>([&](Box& child_box) {
         if (child_box.is_absolutely_positioned())
             return IterationDecision::Continue;
 
         if (child_box.is_floating()) {
-            layout_floating_child(child_box, box);
+            layout_floating_child(child_box, block_container);
             return IterationDecision::Continue;
         }
 
@@ -443,9 +444,9 @@ void BlockFormattingContext::layout_block_level_children(Box& box, LayoutMode la
             compute_position(child_box);
 
         if (is<ReplacedBox>(child_box))
-            place_block_level_replaced_element_in_normal_flow(child_box, box);
+            place_block_level_replaced_element_in_normal_flow(child_box, block_container);
         else if (is<BlockContainer>(child_box))
-            place_block_level_non_replaced_element_in_normal_flow(child_box, box);
+            place_block_level_non_replaced_element_in_normal_flow(child_box, block_container);
 
         // FIXME: This should be factored differently. It's uncool that we mutate the tree *during* layout!
         //        Instead, we should generate the marker box during the tree build.
@@ -458,12 +459,12 @@ void BlockFormattingContext::layout_block_level_children(Box& box, LayoutMode la
     });
 
     if (layout_mode != LayoutMode::Default) {
-        if (box.computed_values().width().is_undefined() || box.computed_values().width().is_auto())
+        if (block_container.computed_values().width().is_undefined() || block_container.computed_values().width().is_auto())
-            box.set_width(content_width);
+            block_container.set_width(content_width);
     }
 }
 
-void BlockFormattingContext::place_block_level_replaced_element_in_normal_flow(Box& child_box, Box& containing_block)
+void BlockFormattingContext::place_block_level_replaced_element_in_normal_flow(Box& child_box, BlockContainer const& containing_block)
 {
     VERIFY(!containing_block.is_absolutely_positioned());
     auto& replaced_element_box_model = child_box.box_model();
@@ -485,7 +486,7 @@ void BlockFormattingContext::place_block_level_replaced_element_in_normal_flow(B
     child_box.set_offset(x, y);
 }
 
-void BlockFormattingContext::place_block_level_non_replaced_element_in_normal_flow(Box& child_box, Box& containing_block)
+void BlockFormattingContext::place_block_level_non_replaced_element_in_normal_flow(Box& child_box, BlockContainer const& containing_block)
 {
     auto& box_model = child_box.box_model();
     auto& computed_values = child_box.computed_values();
@@ -600,7 +601,7 @@ static Gfx::FloatRect rect_in_coordinate_space(const Box& box, const Box& contex
     return rect;
 }
 
-void BlockFormattingContext::layout_floating_child(Box& box, Box& containing_block)
+void BlockFormattingContext::layout_floating_child(Box& box, BlockContainer const& containing_block)
 {
     VERIFY(box.is_floating());
 

Userland/Libraries/LibWeb/Layout/BlockFormattingContext.h

@@ -8,6 +8,7 @@
 
 #include <AK/Vector.h>
 #include <LibWeb/Forward.h>
+#include <LibWeb/Layout/BlockContainer.h>
 #include <LibWeb/Layout/FormattingContext.h>
 
 namespace Web::Layout {
@@ -15,7 +16,7 @@ namespace Web::Layout {
 // https://drafts.csswg.org/css-display/#block-formatting-context
 class BlockFormattingContext : public FormattingContext {
 public:
-    explicit BlockFormattingContext(Box&, FormattingContext* parent);
+    explicit BlockFormattingContext(BlockContainer&, FormattingContext* parent);
     ~BlockFormattingContext();
 
     virtual void run(Box&, LayoutMode) override;
@@ -25,12 +26,12 @@ public:
     const Vector<Box*>& left_floating_boxes() const { return m_left_floating_boxes; }
     const Vector<Box*>& right_floating_boxes() const { return m_right_floating_boxes; }
 
-    static float compute_theoretical_height(const Box&);
+    static float compute_theoretical_height(Box const&);
     void compute_width(Box&);
 
     // https://drafts.csswg.org/css-display/#block-formatting-context-root
-    Box& root() { return context_box(); }
+    BlockContainer& root() { return static_cast<BlockContainer&>(context_box()); }
-    Box const& root() const { return context_box(); }
+    BlockContainer const& root() const { return static_cast<BlockContainer const&>(context_box()); }
 
 protected:
     static void compute_height(Box&);
@@ -45,13 +46,13 @@ private:
 
     void layout_initial_containing_block(LayoutMode);
 
-    void layout_block_level_children(Box&, LayoutMode);
+    void layout_block_level_children(BlockContainer&, LayoutMode);
-    void layout_inline_children(Box&, LayoutMode);
+    void layout_inline_children(BlockContainer&, LayoutMode);
 
-    void place_block_level_replaced_element_in_normal_flow(Box& child, Box& container);
+    void place_block_level_replaced_element_in_normal_flow(Box& child, BlockContainer const&);
-    void place_block_level_non_replaced_element_in_normal_flow(Box& child, Box& container);
+    void place_block_level_non_replaced_element_in_normal_flow(Box& child, BlockContainer const&);
 
-    void layout_floating_child(Box&, Box& containing_block);
+    void layout_floating_child(Box& child, BlockContainer const& containing_block);
 
     void apply_transformations_to_children(Box&);
 

Userland/Libraries/LibWeb/Layout/Box.cpp

@@ -238,19 +238,6 @@ StackingContext* Box::enclosing_stacking_context()
     VERIFY_NOT_REACHED();
 }
 
-LineBox& Box::ensure_last_line_box()
-{
-    if (m_line_boxes.is_empty())
-        return add_line_box();
-    return m_line_boxes.last();
-}
-
-LineBox& Box::add_line_box()
-{
-    m_line_boxes.append(LineBox());
-    return m_line_boxes.last();
-}
-
 float Box::width_of_logical_containing_block() const
 {
     auto* containing_block = this->containing_block();

Userland/Libraries/LibWeb/Layout/Box.h

@@ -8,7 +8,6 @@
 
 #include <AK/OwnPtr.h>
 #include <LibGfx/Rect.h>
-#include <LibWeb/Layout/LineBox.h>
 #include <LibWeb/Layout/Node.h>
 #include <LibWeb/Painting/BorderPainting.h>
 #include <LibWeb/Painting/StackingContext.h>
@@ -118,12 +117,6 @@ public:
     virtual void paint_box_shadow(PaintContext& context);
     virtual void paint_background(PaintContext& context);
 
-    Vector<LineBox>& line_boxes() { return m_line_boxes; }
-    const Vector<LineBox>& line_boxes() const { return m_line_boxes; }
-
-    LineBox& ensure_last_line_box();
-    LineBox& add_line_box();
-
     virtual float width_of_logical_containing_block() const;
 
     Painting::BorderRadiusData normalized_border_radius_data();
@@ -141,8 +134,6 @@ protected:
 
     virtual void did_set_rect() { }
 
-    Vector<LineBox> m_line_boxes;
-
 private:
     virtual bool is_box() const final { return true; }
 

Userland/Libraries/LibWeb/Layout/FlexFormattingContext.cpp

@@ -84,9 +84,10 @@ void FlexFormattingContext::run(Box& box, LayoutMode)
         }
 
         if (!main_constrained && box.children_are_inline()) {
-            BlockFormattingContext bfc(box, this);
+            auto& block_container = verify_cast<BlockContainer>(box);
+            BlockFormattingContext bfc(block_container, this);
             bfc.run(box, LayoutMode::Default);
-            InlineFormattingContext ifc(box, &bfc);
+            InlineFormattingContext ifc(block_container, &bfc);
 
             if (is_row) {
                 ifc.run(box, LayoutMode::OnlyRequiredLineBreaks);
@@ -236,9 +237,10 @@ void FlexFormattingContext::run(Box& box, LayoutMode)
         }
 
         if (!cross_constrained && box.children_are_inline()) {
-            BlockFormattingContext bfc(box, this);
+            auto& block_container = verify_cast<BlockContainer>(box);
+            BlockFormattingContext bfc(block_container, this);
             bfc.run(box, LayoutMode::Default);
-            InlineFormattingContext ifc(box, &bfc);
+            InlineFormattingContext ifc(block_container, &bfc);
             ifc.run(box, LayoutMode::OnlyRequiredLineBreaks);
 
             if (is_row)
@@ -248,7 +250,7 @@ void FlexFormattingContext::run(Box& box, LayoutMode)
         if (is_row) {
             return BlockFormattingContext::compute_theoretical_height(box);
         } else {
-            BlockFormattingContext context(box, this);
+            BlockFormattingContext context(verify_cast<BlockContainer>(box), this);
             context.compute_width(box);
             return box.width();
         }

Userland/Libraries/LibWeb/Layout/FormattingContext.cpp

@@ -94,13 +94,13 @@ void FormattingContext::layout_inside(Box& child_box, LayoutMode layout_mode)
     }
 
     if (creates_block_formatting_context(child_box)) {
-        BlockFormattingContext context(child_box, this);
+        BlockFormattingContext context(verify_cast<BlockContainer>(child_box), this);
         context.run(child_box, layout_mode);
         return;
     }
 
     if (child_display.is_table_inside()) {
-        TableFormattingContext context(child_box, this);
+        TableFormattingContext context(verify_cast<TableBox>(child_box), this);
         context.run(child_box, layout_mode);
         return;
     }
@@ -108,7 +108,7 @@ void FormattingContext::layout_inside(Box& child_box, LayoutMode layout_mode)
     VERIFY(is_block_formatting_context());
 
     if (child_box.children_are_inline()) {
-        InlineFormattingContext context(child_box, this);
+        InlineFormattingContext context(verify_cast<BlockContainer>(child_box), this);
         context.run(child_box, layout_mode);
         return;
     }
@@ -117,11 +117,11 @@ void FormattingContext::layout_inside(Box& child_box, LayoutMode layout_mode)
     run(child_box, layout_mode);
 }
 
-static float greatest_child_width(const Box& box)
+static float greatest_child_width(Box const& box)
 {
     float max_width = 0;
     if (box.children_are_inline()) {
-        for (auto& child : box.line_boxes()) {
+        for (auto& child : verify_cast<BlockContainer>(box).line_boxes()) {
             max_width = max(max_width, child.width());
         }
     } else {
@@ -186,7 +186,7 @@ static Gfx::FloatSize solve_replaced_size_constraint(float w, float h, const Rep
     return { w, h };
 }
 
-static float compute_auto_height_for_block_level_element(const Box& box)
+static float compute_auto_height_for_block_level_element(Box const& box)
 {
     Optional<float> top;
     Optional<float> bottom;
@@ -194,12 +194,13 @@ static float compute_auto_height_for_block_level_element(const Box& box)
     if (box.children_are_inline()) {
         // If it only has inline-level children, the height is the distance between
         // the top of the topmost line box and the bottom of the bottommost line box.
-        if (!box.line_boxes().is_empty()) {
+        auto& block_container = verify_cast<BlockContainer>(box);
-            for (auto& fragment : box.line_boxes().first().fragments()) {
+        if (!block_container.line_boxes().is_empty()) {
+            for (auto& fragment : block_container.line_boxes().first().fragments()) {
                 if (!top.has_value() || fragment.offset().y() < top.value())
                     top = fragment.offset().y();
             }
-            for (auto& fragment : box.line_boxes().last().fragments()) {
+            for (auto& fragment : block_container.line_boxes().last().fragments()) {
                 if (!bottom.has_value() || (fragment.offset().y() + fragment.height()) > bottom.value())
                     bottom = fragment.offset().y() + fragment.height();
             }

Userland/Libraries/LibWeb/Layout/InlineFormattingContext.cpp

@@ -15,7 +15,7 @@
 
 namespace Web::Layout {
 
-InlineFormattingContext::InlineFormattingContext(Box& containing_block, FormattingContext* parent)
+InlineFormattingContext::InlineFormattingContext(BlockContainer& containing_block, FormattingContext* parent)
     : FormattingContext(containing_block, parent)
 {
 }

Userland/Libraries/LibWeb/Layout/InlineFormattingContext.h

@@ -8,17 +8,18 @@
 
 #include <AK/Types.h>
 #include <LibWeb/Forward.h>
+#include <LibWeb/Layout/BlockContainer.h>
 #include <LibWeb/Layout/FormattingContext.h>
 
 namespace Web::Layout {
 
 class InlineFormattingContext final : public FormattingContext {
 public:
-    InlineFormattingContext(Box& containing_block, FormattingContext* parent);
+    InlineFormattingContext(BlockContainer& containing_block, FormattingContext* parent);
     ~InlineFormattingContext();
 
-    Box& containing_block() { return context_box(); }
+    BlockContainer& containing_block() { return static_cast<BlockContainer&>(context_box()); }
-    const Box& containing_block() const { return context_box(); }
+    BlockContainer const& containing_block() const { return static_cast<BlockContainer const&>(context_box()); }
 
     virtual void run(Box&, LayoutMode) override;
 

Userland/Libraries/LibWeb/Layout/InlineNode.cpp

@@ -29,7 +29,7 @@ InlineNode::~InlineNode()
 
 void InlineNode::split_into_lines(InlineFormattingContext& context, LayoutMode layout_mode)
 {
-    auto& containing_block = context.context_box();
+    auto& containing_block = context.containing_block();
 
     if (!computed_values().padding().left.is_undefined_or_auto()) {
         float padding_left = computed_values().padding().left.resolved(CSS::Length::make_px(0), *this, containing_block.width()).to_px(*this);

Userland/Libraries/LibWeb/Layout/TableFormattingContext.cpp

@@ -16,8 +16,8 @@
 
 namespace Web::Layout {
 
-TableFormattingContext::TableFormattingContext(Box& context_box, FormattingContext* parent)
+TableFormattingContext::TableFormattingContext(BlockContainer& block_container, FormattingContext* parent)
-    : BlockFormattingContext(context_box, parent)
+    : BlockFormattingContext(block_container, parent)
 {
 }
 

Userland/Libraries/LibWeb/Layout/TableFormattingContext.h

@@ -13,7 +13,7 @@ namespace Web::Layout {
 
 class TableFormattingContext final : public BlockFormattingContext {
 public:
-    explicit TableFormattingContext(Box&, FormattingContext* parent);
+    explicit TableFormattingContext(BlockContainer&, FormattingContext* parent);
     ~TableFormattingContext();
 
     virtual void run(Box&, LayoutMode) override;