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LibWeb: Bring CSS line-height implementation closer to spec

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We now distribute the line-height evenly between the space above and
below inline-level boxes. This noticeably improves our baseline
alignment in many cases.

Note that the "vertical-align: <length>" case is quite awkward, as the
extra height added by the offset baseline must count towards the line
box height.

There's a lot of room for improvement here, but this makes the buckets
container on Acid3 show up in the right place, with the right size.
This commit is contained in:
Andreas Kling 2022-03-24 22:45:51 +01:00
parent 430559ea51
commit 195ef5e26f
6 changed files with 79 additions and 9 deletions
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45
Userland/Libraries/LibWeb/Layout/LineBoxFragment.cpp
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@ -139,4 +139,49 @@ Gfx::FloatRect LineBoxFragment::selection_rect(const Gfx::Font& font) const
return {};
}
float LineBoxFragment::height_of_inline_level_box(FormattingState const& state) const
{
auto height = [&] {
// From "10.8 Line height calculations: the 'line-height' and 'vertical-align' properties"
// https://www.w3.org/TR/CSS22/visudet.html#line-height
// For replaced elements, inline-block elements, and inline-table elements, this is the height of their margin box.
// FIXME: Support inline-table elements.
if (layout_node().is_replaced_box() || layout_node().is_inline_block()) {
auto const& fragment_box_state = state.get(static_cast<Box const&>(layout_node()));
return fragment_box_state.margin_box_height();
}
// For inline boxes, this is their 'line-height'.
return layout_node().line_height();
}();
if (auto length_percentage = layout_node().computed_values().vertical_align().get_pointer<CSS::LengthPercentage>(); length_percentage && length_percentage->is_length())
height += length_percentage->length().to_px(layout_node());
return height;
}
float LineBoxFragment::top_of_inline_level_box(FormattingState const& state) const
{
// FIXME: Support inline-table elements.
if (layout_node().is_replaced_box() || layout_node().is_inline_block()) {
auto const& fragment_box_state = state.get(static_cast<Box const&>(layout_node()));
return m_offset.y() - fragment_box_state.margin_box_top();
}
return m_offset.y() - (layout_node().line_height() - layout_node().computed_values().font_size()) / 2;
}
float LineBoxFragment::bottom_of_inline_level_box(FormattingState const& state) const
{
auto bottom = [&] {
// FIXME: Support inline-table elements.
if (layout_node().is_replaced_box() || layout_node().is_inline_block()) {
auto const& fragment_box_state = state.get(static_cast<Box const&>(layout_node()));
return m_offset.y() + fragment_box_state.content_height + fragment_box_state.margin_box_bottom();
}
return m_offset.y() + (layout_node().line_height() - layout_node().computed_values().font_size()) / 2;
}();
if (auto length_percentage = layout_node().computed_values().vertical_align().get_pointer<CSS::LengthPercentage>(); length_percentage && length_percentage->is_length())
bottom += length_percentage->length().to_px(layout_node());
return bottom;
}
}