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LibWeb: Split StyleComputer work into two phases with separate outputs

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Before this change, StyleComputer would essentially take a DOM element,
find all the CSS rules that apply to it, and resolve the computed value
for each CSS property for that element.

This worked great, but it meant we had to do all the work of selector
matching and cascading every time.

To enable new optimizations, this change introduces a break in the
middle of this process where we've produced a "CascadedProperties".
This object contains the result of the cascade, before we've begun
turning cascaded values into computed values.

The cascaded properties are now stored with each element, which will
later allow us to do partial updates without re-running the full
StyleComputer machine. This will be particularly valuable for
re-implementing CSS inheritance, which is extremely heavy today.

Note that CSS animations and CSS transitions operate entirely on the
computed values, even though the cascade order would have you believe
they happen earlier. I'm not confident we have the right architecture
for this, but that's a separate issue.
This commit is contained in:
Andreas Kling 2024-12-12 10:06:29 +01:00 • committed by Andreas Kling
parent 4d9f17eddf
commit ed7f4664c2
Notes: github-actions[bot] 2024-12-22 09:14:00 +00:00
60 changed files with 663 additions and 385 deletions
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10
Libraries/LibWeb/HTML/HTMLBodyElement.cpp
View file

@ -41,22 +41,22 @@ void HTMLBodyElement::initialize(JS::Realm& realm)
WEB_SET_PROTOTYPE_FOR_INTERFACE(HTMLBodyElement);
}
void HTMLBodyElement::apply_presentational_hints(CSS::StyleProperties& style) const
void HTMLBodyElement::apply_presentational_hints(GC::Ref<CSS::CascadedProperties> cascaded_properties) const
{
for_each_attribute([&](auto& name, auto& value) {
if (name.equals_ignoring_ascii_case("bgcolor"sv)) {
// https://html.spec.whatwg.org/multipage/rendering.html#the-page:rules-for-parsing-a-legacy-colour-value
auto color = parse_legacy_color_value(value);
if (color.has_value())
style.set_property(CSS::PropertyID::BackgroundColor, CSS::CSSColorValue::create_from_color(color.value()));
cascaded_properties->set_property_from_presentational_hint(CSS::PropertyID::BackgroundColor, CSS::CSSColorValue::create_from_color(color.value()));
} else if (name.equals_ignoring_ascii_case("text"sv)) {
// https://html.spec.whatwg.org/multipage/rendering.html#the-page:rules-for-parsing-a-legacy-colour-value-2
auto color = parse_legacy_color_value(value);
if (color.has_value())
style.set_property(CSS::PropertyID::Color, CSS::CSSColorValue::create_from_color(color.value()));
cascaded_properties->set_property_from_presentational_hint(CSS::PropertyID::Color, CSS::CSSColorValue::create_from_color(color.value()));
} else if (name.equals_ignoring_ascii_case("background"sv)) {
VERIFY(m_background_style_value);
style.set_property(CSS::PropertyID::BackgroundImage, *m_background_style_value);
cascaded_properties->set_property_from_presentational_hint(CSS::PropertyID::BackgroundImage, *m_background_style_value);
}
});
@ -84,7 +84,7 @@ void HTMLBodyElement::apply_presentational_hints(CSS::StyleProperties& style) co
if (!value.has_value())
return;
if (auto parsed_value = parse_non_negative_integer(value.value()); parsed_value.has_value())
style.set_property(property_id, CSS::LengthStyleValue::create(CSS::Length::make_px(*parsed_value)));
cascaded_properties->set_property_from_presentational_hint(property_id, CSS::LengthStyleValue::create(CSS::Length::make_px(*parsed_value)));
};
apply_margin_value(CSS::PropertyID::MarginTop, margin_top_value);