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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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23
Userland/Libraries/LibWeb/CSS/StyleProperties.cpp
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@ -154,8 +154,8 @@ NonnullRefPtr<Gfx::Font const> StyleProperties::font_fallback(bool monospace, bo
return Platform::FontPlugin::the().default_font();
}
// FIXME: This implementation is almost identical to line_height(Layout::Node) below. Maybe they can be combined somehow.
CSSPixels StyleProperties::line_height(CSSPixelRect const& viewport_rect, Length::FontMetrics const& font_metrics, Length::FontMetrics const& root_font_metrics) const
// FIXME: This implementation is almost identical to compute_line_height(Layout::Node) below. Maybe they can be combined somehow.
CSSPixels StyleProperties::compute_line_height(CSSPixelRect const& viewport_rect, Length::FontMetrics const& font_metrics, Length::FontMetrics const& root_font_metrics) const
{
auto line_height = property(CSS::PropertyID::LineHeight);
@ -178,14 +178,27 @@ CSSPixels StyleProperties::line_height(CSSPixelRect const& viewport_rect, Length
}
if (line_height->is_calculated()) {
// FIXME: Handle `line-height: calc(...)` despite not having a LayoutNode here.
return font_metrics.line_height;
if (line_height->as_calculated().resolves_to_number()) {
auto resolved = line_height->as_calculated().resolve_number();
if (!resolved.has_value()) {
dbgln("FIXME: Failed to resolve calc() line-height (number): {}", line_height->as_calculated().to_string());
return CSSPixels::nearest_value_for(m_font_list->first().pixel_metrics().line_spacing());
}
return Length(resolved.value(), Length::Type::Em).to_px(viewport_rect, font_metrics, root_font_metrics);
}
auto resolved = line_height->as_calculated().resolve_length(Length::ResolutionContext { viewport_rect, font_metrics, root_font_metrics });
if (!resolved.has_value()) {
dbgln("FIXME: Failed to resolve calc() line-height: {}", line_height->as_calculated().to_string());
return CSSPixels::nearest_value_for(m_font_list->first().pixel_metrics().line_spacing());
}
return resolved->to_px(viewport_rect, font_metrics, root_font_metrics);
}
return font_metrics.line_height;
}
CSSPixels StyleProperties::line_height(Layout::Node const& layout_node) const
CSSPixels StyleProperties::compute_line_height(Layout::Node const& layout_node) const
{
auto line_height = property(CSS::PropertyID::LineHeight);