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LibWeb: Parse the will-change property

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This property provides a hint to the rendering engine about properties
that are likely to change in the near future, allowing for early
optimizations to be applied.
This commit is contained in:
Tim Ledbetter 2025-08-16 08:39:18 +01:00 • committed by Sam Atkins
commit 4f663ca6e7
Notes: github-actions[bot] 2025-08-18 11:37:59 +00:00
16 changed files with 335 additions and 2 deletions
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42
Libraries/LibWeb/CSS/ComputedProperties.cpp
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@ -1911,4 +1911,46 @@ ScrollbarWidth ComputedProperties::scrollbar_width() const
return keyword_to_scrollbar_width(value.to_keyword()).release_value();
}
WillChange ComputedProperties::will_change() const
{
auto const& value = property(PropertyID::WillChange);
if (value.to_keyword() == Keyword::Auto)
return WillChange::make_auto();
auto to_will_change_entry = [](StyleValue const& value) -> Optional<WillChange::WillChangeEntry> {
if (value.is_keyword()) {
switch (value.as_keyword().keyword()) {
case Keyword::Contents:
return WillChange::Type::Contents;
case Keyword::ScrollPosition:
return WillChange::Type::ScrollPosition;
default:
VERIFY_NOT_REACHED();
}
}
VERIFY(value.is_custom_ident());
auto custom_ident = value.as_custom_ident().custom_ident();
auto property_id = property_id_from_string(custom_ident);
if (!property_id.has_value())
return {};
return property_id.release_value();
};
if (value.is_value_list()) {
auto const& value_list = value.as_value_list();
Vector<WillChange::WillChangeEntry> will_change_entries;
for (auto const& style_value : value_list.values()) {
if (auto entry = to_will_change_entry(*style_value); entry.has_value())
will_change_entries.append(*entry);
}
return WillChange(move(will_change_entries));
}
auto will_change_entry = to_will_change_entry(value);
if (will_change_entry.has_value())
return WillChange({ *will_change_entry });
return WillChange::make_auto();
}
}