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LibWeb: Retain calculated Element::ordinal_value for lists

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`Element::ordinal_value` is called for every `li` element in
a list (ul, ol, menu).

Before:
  `ordinal_value` iterates through all of the children of the list
  owner. It is called once for each element: complexity $O(n^2)$.

After:
  - Save the result of the first calculation in `m_ordinal_value`
  then return it in subsequent calls.
  - Tree modifications are intercepted and trigger invalidation
    of the first node's `m_ordinal_value`:
    - insert_before
    - append
    - remove
  Results in noticeable performance improvement rendering' large
  lists: from 20s to 4s for 20K elements.
This commit is contained in:
Manuel Zahariev 2025-05-13 06:59:03 -07:00 • committed by Sam Atkins
commit 00d43b39d1
Notes: github-actions[bot] 2025-06-16 11:46:28 +00:00
5 changed files with 137 additions and 54 deletions
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47
Libraries/LibWeb/DOM/Element.h
View file

@ -6,6 +6,7 @@
#pragma once
#include <AK/IterationDecision.h>
#include <AK/Optional.h>
#include <LibWeb/ARIA/ARIAMixin.h>
#include <LibWeb/ARIA/AttributeNames.h>
@ -14,6 +15,7 @@
#include <LibWeb/Bindings/Intrinsics.h>
#include <LibWeb/Bindings/ShadowRootPrototype.h>
#include <LibWeb/CSS/CascadedProperties.h>
#include <LibWeb/CSS/ComputedProperties.h>
#include <LibWeb/CSS/CountersSet.h>
#include <LibWeb/CSS/Selector.h>
#include <LibWeb/CSS/StyleInvalidation.h>
@ -465,9 +467,46 @@ public:
return affected_by_direct_sibling_combinator() || affected_by_indirect_sibling_combinator() || affected_by_sibling_position_or_count_pseudo_class() || affected_by_nth_child_pseudo_class();
}
size_t number_of_owned_list_items() const;
i32 number_of_owned_list_items() const;
Element* list_owner() const;
size_t ordinal_value() const;
void maybe_invalidate_ordinals_for_list_owner(Optional<Element*> skip_node = {});
i32 ordinal_value();
template<typename Callback>
void for_each_numbered_item_owned_by_list_owner(Callback callback) const
{
const_cast<Element*>(this)->for_each_numbered_item_owned_by_list_owner(move(callback));
}
template<typename Callback>
void for_each_numbered_item_owned_by_list_owner(Callback callback)
{
for (auto* node = this->first_child(); node != nullptr; node = node->next_in_pre_order(this)) {
if (!is<Element>(*node))
continue;
static_cast<Element*>(node)->m_is_contained_in_list_subtree = true;
if (node->is_html_ol_ul_menu_element()) {
// Skip list nodes and their descendents. They have their own, unrelated ordinals.
while (node->last_child() != nullptr) // Find the last node (preorder) in the subtree headed by node. O(1).
node = node->last_child();
continue;
}
if (!node->layout_node())
continue; // Skip nodes that do not participate in the layout.
auto* element = static_cast<Element*>(node);
if (!element->computed_properties()->display().is_list_item())
continue; // Skip nodes that are not list items.
if (callback(element) == IterationDecision::Break)
return;
}
}
void set_pointer_capture(WebIDL::Long pointer_id);
void release_pointer_capture(WebIDL::Long pointer_id);
@ -594,6 +633,10 @@ private:
// https://drafts.csswg.org/css-contain/#proximity-to-the-viewport
ProximityToTheViewport m_proximity_to_the_viewport { ProximityToTheViewport::NotDetermined };
// https://html.spec.whatwg.org/multipage/grouping-content.html#ordinal-value
Optional<i32> m_ordinal_value;
bool m_is_contained_in_list_subtree { false };
};
template<>