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LibWeb: Invalidate less elements affected by CSS custom properties

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Before this change, whenever element's attributes changed, we would add
a flag to "pending invalidation", indicating that all descendants whose
style uses CSS custom properties needed to be recomputed. This resulted
in severe overinvalidation, because we would run invalidation regardless
of whether any custom property on affected element actually changed.

This change takes another approach, and now we decide whether
descendant's style needs to be recomputed based on whether ancestor's
style recomputation results in a change of custom properties, though
this approach adds a little overhead to style computation as now we have
to compare old vs new hashmap of custom properties.

This brings substantial improvement on discord and x.com where, before
this change, advantage of using invalidation sets was lost and we had
to recompute all descendants, because almost all of them use custom
properties.
This commit is contained in:
Aliaksandr Kalenik 2025-07-27 19:41:21 +02:00 • committed by Andreas Kling
commit d1fbb7b51e
Notes: github-actions[bot] 2025-07-30 09:07:23 +00:00
13 changed files with 71 additions and 67 deletions
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21
Libraries/LibWeb/DOM/Element.cpp
View file

@ -683,10 +683,12 @@ static CSS::RequiredInvalidationAfterStyleChange compute_required_invalidation(C
return invalidation;
}
CSS::RequiredInvalidationAfterStyleChange Element::recompute_style()
CSS::RequiredInvalidationAfterStyleChange Element::recompute_style(bool& did_change_custom_properties)
{
VERIFY(parent());
m_style_uses_attr_css_function = false;
m_style_uses_var_css_function = false;
m_affected_by_has_pseudo_class_in_subject_position = false;
m_affected_by_has_pseudo_class_in_non_subject_position = false;
m_affected_by_has_pseudo_class_with_relative_selector_that_has_sibling_combinator = false;
@ -697,7 +699,7 @@ CSS::RequiredInvalidationAfterStyleChange Element::recompute_style()
m_sibling_invalidation_distance = 0;
auto& style_computer = document().style_computer();
auto new_computed_properties = style_computer.compute_style(*this);
auto new_computed_properties = style_computer.compute_style(*this, {}, did_change_custom_properties);
// Tables must not inherit -libweb-* values for text-align.
// FIXME: Find the spec for this.
@ -737,7 +739,7 @@ CSS::RequiredInvalidationAfterStyleChange Element::recompute_style()
style_computer.push_ancestor(*this);
auto pseudo_element_style = computed_properties(pseudo_element);
auto new_pseudo_element_style = style_computer.compute_pseudo_element_style_if_needed(*this, pseudo_element);
auto new_pseudo_element_style = style_computer.compute_pseudo_element_style_if_needed(*this, pseudo_element, did_change_custom_properties);
// TODO: Can we be smarter about invalidation?
if (pseudo_element_style && new_pseudo_element_style) {
@ -2472,24 +2474,13 @@ void Element::invalidate_style_after_attribute_change(FlyString const& attribute
{
Vector<CSS::InvalidationSet::Property, 1> changed_properties;
StyleInvalidationOptions style_invalidation_options;
if (is_presentational_hint(attribute_name)) {
if (is_presentational_hint(attribute_name) || style_uses_attr_css_function()) {
style_invalidation_options.invalidate_self = true;
}
if (style_uses_css_custom_properties()) {
// A css custom property can be hooked on to this element by any attribute
// so invalidate elements and rerender them in that scenario
style_invalidation_options.invalidate_elements_that_use_css_custom_properties = true;
}
if (attribute_name == HTML::AttributeNames::style) {
style_invalidation_options.invalidate_self = true;
// even if we don't have custom properties, the new "style" attribute could add one
style_invalidation_options.invalidate_elements_that_use_css_custom_properties = true;
} else if (attribute_name == HTML::AttributeNames::class_) {
// adding or removing classes can add new custom properties to this element
style_invalidation_options.invalidate_elements_that_use_css_custom_properties = true;
Vector<StringView> old_classes;
Vector<StringView> new_classes;
if (old_value.has_value())