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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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10
Userland/Libraries/LibWeb/CSS/Length.cpp
View file

@ -19,14 +19,14 @@
namespace Web::CSS {
Length::FontMetrics::FontMetrics(CSSPixels font_size, Gfx::FontPixelMetrics const& pixel_metrics, CSSPixels line_height)
Length::FontMetrics::FontMetrics(CSSPixels font_size, Gfx::FontPixelMetrics const& pixel_metrics)
: font_size(font_size)
, x_height(pixel_metrics.x_height)
// FIXME: This is only approximately the cap height. The spec suggests measuring the "O" glyph:
// https://www.w3.org/TR/css-values-4/#cap
, cap_height(pixel_metrics.ascent)
, zero_advance(pixel_metrics.advance_of_ascii_zero + pixel_metrics.glyph_spacing)
, line_height(line_height)
, line_height(round(pixel_metrics.line_spacing()))
{
}
@ -138,8 +138,8 @@ Length::ResolutionContext Length::ResolutionContext::for_layout_node(Layout::Nod
VERIFY(root_element->layout_node());
return Length::ResolutionContext {
.viewport_rect = node.navigable()->viewport_rect(),
.font_metrics = { node.computed_values().font_size(), node.first_available_font().pixel_metrics(), node.line_height() },
.root_font_metrics = { root_element->layout_node()->computed_values().font_size(), root_element->layout_node()->first_available_font().pixel_metrics(), root_element->layout_node()->line_height() },
.font_metrics = { node.computed_values().font_size(), node.first_available_font().pixel_metrics() },
.root_font_metrics = { root_element->layout_node()->computed_values().font_size(), root_element->layout_node()->first_available_font().pixel_metrics() },
};
}
@ -170,12 +170,10 @@ CSSPixels Length::to_px(Layout::Node const& layout_node) const
FontMetrics font_metrics {
layout_node.computed_values().font_size(),
layout_node.first_available_font().pixel_metrics(),
layout_node.line_height()
};
FontMetrics root_font_metrics {
root_element->layout_node()->computed_values().font_size(),
root_element->layout_node()->first_available_font().pixel_metrics(),
root_element->layout_node()->line_height()
};
return font_relative_length_to_px(font_metrics, root_font_metrics);