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LibWeb: Compute containing block boxes once at start of layout

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We now cache the containing block (box) once at the start of layout,
which allows Layout::Node::containing_block() to return instantly
instead of doing tree traversal.

Removes a 0.7% profile item on Speedometer 3.
This commit is contained in:
Andreas Kling 2025-04-18 11:39:23 +02:00
parent 3b4a184f1a
commit 8f7f4ba43b
4 changed files with 32 additions and 17 deletions
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9
Libraries/LibWeb/DOM/Document.cpp
View file

@ -1322,6 +1322,11 @@ void Document::update_layout(UpdateLayoutReason reason)
}
}
m_layout_root->for_each_in_inclusive_subtree([&](auto& layout_node) {
layout_node.recompute_containing_block({});
return TraversalDecision::Continue;
});
m_layout_root->for_each_in_inclusive_subtree_of_type<Layout::Box>([&](auto& child) {
if (auto dom_node = child.dom_node(); dom_node && dom_node->is_element()) {
child.set_has_size_containment(as<Element>(*dom_node).has_size_containment());
@ -1338,8 +1343,8 @@ void Document::update_layout(UpdateLayoutReason reason)
m_layout_root->for_each_in_inclusive_subtree_of_type<Layout::Box>([&](auto& child) {
if (!child.is_absolutely_positioned())
return TraversalDecision::Continue;
if (auto* containing_block = child.containing_block()) {
auto* closest_box_that_establishes_formatting_context = containing_block;
if (auto containing_block = child.containing_block()) {
auto closest_box_that_establishes_formatting_context = containing_block;
while (closest_box_that_establishes_formatting_context) {
if (closest_box_that_establishes_formatting_context == m_layout_root)
break;

4
Libraries/LibWeb/Layout/BlockFormattingContext.cpp
View file

@ -638,7 +638,7 @@ CSSPixels BlockFormattingContext::compute_auto_height_for_block_level_element(Bo
static CSSPixels containing_block_height_to_resolve_percentage_in_quirks_mode(Box const& box, LayoutState const& state)
{
// https://quirks.spec.whatwg.org/#the-percentage-height-calculation-quirk
auto const* containing_block = box.containing_block();
auto containing_block = box.containing_block();
while (containing_block) {
// 1. Let element be the nearest ancestor containing block of element, if there is one.
// Otherwise, return the initial containing block.
@ -925,7 +925,7 @@ BlockFormattingContext::DidIntroduceClearance BlockFormattingContext::clear_floa
// Then, convert the clearance Y to a coordinate relative to the containing block of `child_box`.
CSSPixels clearance_y_in_containing_block = clearance_y_in_root;
for (auto* containing_block = child_box.containing_block(); containing_block && containing_block != &root(); containing_block = containing_block->containing_block())
for (auto containing_block = child_box.containing_block(); containing_block && containing_block != &root(); containing_block = containing_block->containing_block())
clearance_y_in_containing_block -= m_state.get(*containing_block).offset.y();
if (inline_formatting_context.has_value()) {

28
Libraries/LibWeb/Layout/Node.cpp
View file

@ -53,6 +53,7 @@ void Node::visit_edges(Cell::Visitor& visitor)
for (auto const& paintable : m_paintable) {
visitor.visit(GC::Ptr { &paintable });
}
visitor.visit(m_containing_block);
visitor.visit(m_pseudo_element_generator);
TreeNode::visit_edges(visitor);
}
@ -106,9 +107,9 @@ bool Node::can_contain_boxes_with_position_absolute() const
return false;
}
static Box const* nearest_ancestor_capable_of_forming_a_containing_block(Node const& node)
static GC::Ptr<Box> nearest_ancestor_capable_of_forming_a_containing_block(Node& node)
{
for (auto const* ancestor = node.parent(); ancestor; ancestor = ancestor->parent()) {
for (auto* ancestor = node.parent(); ancestor; ancestor = ancestor->parent()) {
if (ancestor->is_block_container()
|| ancestor->display().is_flex_inside()
|| ancestor->display().is_grid_inside()
@ -119,31 +120,36 @@ static Box const* nearest_ancestor_capable_of_forming_a_containing_block(Node co
return nullptr;
}
Box const* Node::containing_block() const
void Node::recompute_containing_block(Badge<DOM::Document>)
{
if (is<TextNode>(*this))
return nearest_ancestor_capable_of_forming_a_containing_block(*this);
if (is<TextNode>(*this)) {
m_containing_block = nearest_ancestor_capable_of_forming_a_containing_block(*this);
return;
}
auto position = computed_values().position();
// https://drafts.csswg.org/css-position-3/#absolute-cb
if (position == CSS::Positioning::Absolute) {
auto const* ancestor = parent();
auto* ancestor = parent();
while (ancestor && !ancestor->can_contain_boxes_with_position_absolute())
ancestor = ancestor->parent();
return static_cast<Box const*>(ancestor);
m_containing_block = static_cast<Box*>(ancestor);
return;
}
if (position == CSS::Positioning::Fixed)
return &root();
if (position == CSS::Positioning::Fixed) {
m_containing_block = &root();
return;
}
return nearest_ancestor_capable_of_forming_a_containing_block(*this);
m_containing_block = nearest_ancestor_capable_of_forming_a_containing_block(*this);
}
// returns containing block this node would have had if its position was static
Box const* Node::static_position_containing_block() const
{
return nearest_ancestor_capable_of_forming_a_containing_block(*this);
return nearest_ancestor_capable_of_forming_a_containing_block(const_cast<Node&>(*this));
}
Box const* Node::non_anonymous_containing_block() const

8
Libraries/LibWeb/Layout/Node.h
View file

@ -127,8 +127,10 @@ public:
bool is_grid_item() const { return m_is_grid_item; }
void set_grid_item(bool b) { m_is_grid_item = b; }
Box const* containing_block() const;
Box* containing_block() { return const_cast<Box*>(const_cast<Node const*>(this)->containing_block()); }
[[nodiscard]] GC::Ptr<Box const> containing_block() const { return m_containing_block; }
[[nodiscard]] GC::Ptr<Box> containing_block() { return m_containing_block; }
void recompute_containing_block(Badge<DOM::Document>);
[[nodiscard]] Box const* static_position_containing_block() const;
[[nodiscard]] Box* static_position_containing_block() { return const_cast<Box*>(const_cast<Node const*>(this)->static_position_containing_block()); }
@ -200,6 +202,8 @@ private:
GC::Ref<DOM::Node> m_dom_node;
PaintableList m_paintable;
GC::Ptr<Box> m_containing_block;
GC::Ptr<DOM::Element> m_pseudo_element_generator;
bool m_anonymous { false };