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LibWeb: Prevent infinitely growing font size due to rem units in root

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A font-size with rem units need to resolve against the default font
metrics for the root element, otherwise every time we compute style,
the reference value for rem units grows.

This fixes an issue where text on some web pages would grow every time
there was a relayout. This was very noticeable on https://proton.me/

Fixes #339
This commit is contained in:
Andreas Kling 2025-03-05 18:22:05 +01:00 • committed by Andreas Kling
parent dd78d5d50e
commit 02a642b87b
Notes: github-actions[bot] 2025-03-05 21:47:05 +00:00
5 changed files with 45 additions and 8 deletions
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19
Libraries/LibWeb/CSS/StyleComputer.cpp
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@ -1877,7 +1877,7 @@ RefPtr<Gfx::FontCascadeList const> StyleComputer::compute_font_for_style_values(
auto length = value.as_length().length();
if (length.is_absolute() || length.is_relative()) {
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 length.to_px(viewport_rect(), font_metrics, root_element_font_metrics_for_element(element));
}
}
return font_size_in_px;
@ -1942,7 +1942,7 @@ RefPtr<Gfx::FontCascadeList const> StyleComputer::compute_font_for_style_values(
Length::ResolutionContext const length_resolution_context {
.viewport_rect = viewport_rect(),
.font_metrics = Length::FontMetrics { parent_font_size, font_pixel_metrics },
.root_font_metrics = m_root_element_font_metrics,
.root_font_metrics = root_element_font_metrics_for_element(element),
};
Optional<Length> maybe_length;
@ -2128,10 +2128,10 @@ Gfx::Font const& StyleComputer::initial_font() const
return ComputedProperties::font_fallback(false, false, 12);
}
void StyleComputer::absolutize_values(ComputedProperties& style) const
void StyleComputer::absolutize_values(ComputedProperties& style, GC::Ptr<DOM::Element const> element) const
{
Length::FontMetrics font_metrics {
m_root_element_font_metrics.font_size,
root_element_font_metrics_for_element(element).font_size,
style.first_available_computed_font().pixel_metrics()
};
@ -2359,7 +2359,7 @@ GC::Ref<ComputedProperties> StyleComputer::create_document_style() const
compute_math_depth(style, nullptr, {});
compute_font(style, nullptr, {});
compute_defaulted_values(style, nullptr, {});
absolutize_values(style);
absolutize_values(style, nullptr);
style->set_property(CSS::PropertyID::Width, CSS::LengthStyleValue::create(CSS::Length::make_px(viewport_rect().width())));
style->set_property(CSS::PropertyID::Height, CSS::LengthStyleValue::create(CSS::Length::make_px(viewport_rect().height())));
style->set_property(CSS::PropertyID::Display, CSS::DisplayStyleValue::create(CSS::Display::from_short(CSS::Display::Short::Block)));
@ -2644,7 +2644,7 @@ GC::Ref<ComputedProperties> StyleComputer::compute_properties(DOM::Element& elem
compute_font(computed_style, &element, pseudo_element);
// 4. Absolutize values, turning font/viewport relative lengths into absolute lengths
absolutize_values(computed_style);
absolutize_values(computed_style, element);
// 5. Default the values, applying inheritance and 'initial' as needed
compute_defaulted_values(computed_style, &element, pseudo_element);
@ -3267,4 +3267,11 @@ void RuleCache::for_each_matching_rules(DOM::Element const& element, Optional<Se
(void)callback(other_rules);
}
Length::FontMetrics const& StyleComputer::root_element_font_metrics_for_element(GC::Ptr<DOM::Element const> element) const
{
if (element && element->document().document_element() == element)
return m_default_font_metrics;
return m_root_element_font_metrics;
}
}