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LibWeb: Bring CSS line-height closer to other engines

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This patch makes a few changes to the way we calculate line-height:

- `line-height: normal` is now resolved using metrics from the used
  font (specifically, round(A + D + lineGap)).

- `line-height: calc(...)` is now resolved at style compute time.

- `line-height` values are now absolutized at style compute time.

As a consequence of the above, we no longer need to walk the DOM
ancestor chain looking for line-heights during style computation.
Instead, values are inherited, resolved and absolutized locally.

This is not only much faster, but also makes our line-height metrics
match those of other engines like Gecko and Blink.
This commit is contained in:
Andreas Kling 2024-01-12 12:39:40 +01:00
parent f0722671c3
commit e7de5cb4d2
385 changed files with 6889 additions and 6893 deletions
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48
Userland/Libraries/LibWeb/CSS/StyleComputer.cpp
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@ -81,7 +81,7 @@ static NonnullRefPtr<StyleValue const> get_inherit_value(JS::Realm& initial_valu
StyleComputer::StyleComputer(DOM::Document& document)
: m_document(document)
, m_default_font_metrics(16, Gfx::FontDatabase::default_font().pixel_metrics(), 16)
, m_default_font_metrics(16, Gfx::FontDatabase::default_font().pixel_metrics())
, m_root_element_font_metrics(m_default_font_metrics)
{
}
@ -1529,9 +1529,9 @@ Length::FontMetrics StyleComputer::calculate_root_element_font_metrics(StyleProp
auto root_value = style.property(CSS::PropertyID::FontSize);
auto font_pixel_metrics = style.first_available_computed_font().pixel_metrics();
Length::FontMetrics font_metrics { m_default_font_metrics.font_size, font_pixel_metrics, CSSPixels::nearest_value_for(font_pixel_metrics.line_spacing()) };
Length::FontMetrics font_metrics { m_default_font_metrics.font_size, font_pixel_metrics };
font_metrics.font_size = root_value->as_length().length().to_px(viewport_rect(), font_metrics, font_metrics);
font_metrics.line_height = style.line_height(viewport_rect(), font_metrics, font_metrics);
font_metrics.line_height = style.compute_line_height(viewport_rect(), font_metrics, font_metrics);
return font_metrics;
}
@ -1645,7 +1645,6 @@ RefPtr<Gfx::FontCascadeList const> StyleComputer::compute_font_for_style_values(
// FIXME: Should be based on "user's default font size"
CSSPixels font_size_in_px = 16;
auto parent_line_height = parent_or_root_element_line_height(element, pseudo_element);
Gfx::FontPixelMetrics font_pixel_metrics;
if (parent_element && parent_element->computed_css_values())
font_pixel_metrics = parent_element->computed_css_values()->first_available_computed_font().pixel_metrics();
@ -1657,15 +1656,14 @@ RefPtr<Gfx::FontCascadeList const> StyleComputer::compute_font_for_style_values(
auto value = parent_element->computed_css_values()->property(CSS::PropertyID::FontSize);
if (value->is_length()) {
auto length = value->as_length().length();
auto parent_line_height = parent_or_root_element_line_height(parent_element, {});
if (length.is_absolute() || length.is_relative()) {
Length::FontMetrics font_metrics { font_size_in_px, font_pixel_metrics, parent_line_height };
Length::FontMetrics font_metrics { font_size_in_px, font_pixel_metrics };
return length.to_px(viewport_rect(), font_metrics, m_root_element_font_metrics);
}
}
return font_size_in_px;
};
Length::FontMetrics font_metrics { parent_font_size(), font_pixel_metrics, parent_line_height };
Length::FontMetrics font_metrics { parent_font_size(), font_pixel_metrics };
if (font_size.is_identifier()) {
// https://w3c.github.io/csswg-drafts/css-fonts/#absolute-size-mapping
@ -1924,30 +1922,12 @@ Gfx::Font const& StyleComputer::initial_font() const
return StyleProperties::font_fallback(false, false);
}
CSSPixels StyleComputer::parent_or_root_element_line_height(DOM::Element const* element, Optional<CSS::Selector::PseudoElement::Type> pseudo_element) const
void StyleComputer::absolutize_values(StyleProperties& style) const
{
auto* parent_element = element_to_inherit_style_from(element, pseudo_element);
if (!parent_element)
return m_root_element_font_metrics.line_height;
auto const* computed_values = parent_element->computed_css_values();
if (!computed_values)
return m_root_element_font_metrics.line_height;
auto parent_font_pixel_metrics = computed_values->first_available_computed_font().pixel_metrics();
auto parent_font_size = computed_values->property(CSS::PropertyID::FontSize)->as_length().length();
// FIXME: Can the parent font size be non-absolute here?
auto parent_font_size_value = parent_font_size.is_absolute() ? parent_font_size.absolute_length_to_px() : m_root_element_font_metrics.font_size;
auto parent_parent_line_height = parent_or_root_element_line_height(parent_element, {});
Length::FontMetrics parent_font_metrics { parent_font_size_value, parent_font_pixel_metrics, parent_parent_line_height };
return computed_values->line_height(viewport_rect(), parent_font_metrics, m_root_element_font_metrics);
}
void StyleComputer::absolutize_values(StyleProperties& style, DOM::Element const* element, Optional<CSS::Selector::PseudoElement::Type> pseudo_element) const
{
auto parent_or_root_line_height = parent_or_root_element_line_height(element, pseudo_element);
auto font_pixel_metrics = style.first_available_computed_font().pixel_metrics();
Length::FontMetrics font_metrics { m_root_element_font_metrics.font_size, font_pixel_metrics, parent_or_root_line_height };
Length::FontMetrics font_metrics {
m_root_element_font_metrics.font_size,
style.first_available_computed_font().pixel_metrics()
};
auto font_size = style.property(CSS::PropertyID::FontSize)->as_length().length().to_px(viewport_rect(), font_metrics, m_root_element_font_metrics);
font_metrics.font_size = font_size;
@ -1962,7 +1942,7 @@ void StyleComputer::absolutize_values(StyleProperties& style, DOM::Element const
Length::make_px(CSSPixels::nearest_value_for(font_size * static_cast<double>((*line_height_value_slot)->as_percentage().percentage().as_fraction()))));
}
auto line_height = style.line_height(viewport_rect(), font_metrics, m_root_element_font_metrics);
auto line_height = style.compute_line_height(viewport_rect(), font_metrics, m_root_element_font_metrics);
font_metrics.line_height = line_height;
// NOTE: line-height might be using lh which should be resolved against the parent line height (like we did here already)
@ -1975,6 +1955,8 @@ void StyleComputer::absolutize_values(StyleProperties& style, DOM::Element const
continue;
value_slot->style = value_slot->style->absolutized(viewport_rect(), font_metrics, m_root_element_font_metrics);
}
style.set_line_height({}, line_height);
}
enum class BoxTypeTransformation {
@ -2098,7 +2080,7 @@ NonnullRefPtr<StyleProperties> StyleComputer::create_document_style() const
compute_math_depth(style, nullptr, {});
compute_font(style, nullptr, {});
compute_defaulted_values(style, nullptr, {});
absolutize_values(style, nullptr, {});
absolutize_values(style);
style->set_property(CSS::PropertyID::Width, CSS::LengthStyleValue::create(CSS::Length::make_px(viewport_rect().width())), nullptr);
style->set_property(CSS::PropertyID::Height, CSS::LengthStyleValue::create(CSS::Length::make_px(viewport_rect().height())), nullptr);
style->set_property(CSS::PropertyID::Display, CSS::DisplayStyleValue::create(CSS::Display::from_short(CSS::Display::Short::Block)), nullptr);
@ -2149,7 +2131,7 @@ ErrorOr<RefPtr<StyleProperties>> StyleComputer::compute_style_impl(DOM::Element&
compute_font(style, &element, pseudo_element);
// 4. Absolutize values, turning font/viewport relative lengths into absolute lengths
absolutize_values(style, &element, pseudo_element);
absolutize_values(style);
// 5. Default the values, applying inheritance and 'initial' as needed
compute_defaulted_values(style, &element, pseudo_element);