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LibWeb: Bucket hover rules using RuleCache

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Analysis of selectors on modern websites shows that the `:hover`
pseudo-class is mostly used in the subject position within relatively
simple selectors like `.a:hover`. This suggests that we could greatly
benefit from segregating them by id/class/tag name, this way reducing
number of selectors tested during hover style invalidation.

With this change, hover invalidation on Discord goes down from 70ms to
3ms on my machine. I also tested GMail and GitHub where this change
shows nice 2x-3x speedup.
This commit is contained in:
Aliaksandr Kalenik 2025-02-20 21:53:31 +01:00 • committed by Alexander Kalenik
commit 0ab61a94d7
Notes: github-actions[bot] 2025-02-22 09:15:47 +00:00
3 changed files with 28 additions and 23 deletions
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24
Libraries/LibWeb/DOM/Document.cpp
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@ -1726,8 +1726,6 @@ void Document::invalidate_style_of_elements_affected_by_has()
void Document::invalidate_style_for_elements_affected_by_hover_change(Node& old_new_hovered_common_ancestor, GC::Ptr<Node> hovered_node)
{
auto const& hover_rules = style_computer().get_hover_rules();
if (hover_rules.is_empty())
return;
auto& root = old_new_hovered_common_ancestor.root();
auto shadow_root = is<ShadowRoot>(root) ? static_cast<ShadowRoot const*>(&root) : nullptr;
@ -1761,14 +1759,20 @@ void Document::invalidate_style_for_elements_affected_by_hover_change(Node& old_
};
auto matches_different_set_of_hover_rules_after_hovered_element_change = [&](Element const& element) {
for (auto const& rule : hover_rules) {
bool before = does_rule_match_on_element(element, rule);
TemporaryChange change { m_hovered_node, hovered_node };
bool after = does_rule_match_on_element(element, rule);
if (before != after)
return true;
}
return false;
bool result = false;
hover_rules.for_each_matching_rules(element, {}, [&](auto& rules) {
for (auto& rule : rules) {
bool before = does_rule_match_on_element(element, rule);
TemporaryChange change { m_hovered_node, hovered_node };
bool after = does_rule_match_on_element(element, rule);
if (before != after) {
result = true;
return IterationDecision::Break;
}
}
return IterationDecision::Continue;
});
return result;
};
Function<void(Node&)> invalidate_hovered_elements_recursively = [&](Node& node) -> void {