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layout: Move text decoration propagation to stacking context tree construction (#37069)

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Text decorations have a special kind of propagation. Instead of
propating these during box tree construction, move propagation to
stacking context tree construction. This will allow for using a very
easy type of incremental layout when text decorations change. For
instance, when a link changes color during hovering over it, we can skip
all of box and fragment tree construction.

In addition, propagation works a bit better now and color and style
properly move down from their originating `Fragment`s.

This introduces three new failures, because now we are drawing the
text-decoration with the correct color in more places, which exposes an
issue we have with text-decorations not being drawn in relation to the
baseline (taking into account `vertical-align`).

Testing: There are tests for these changes.
Fixes #31736.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Oriol Brufau <obrufau@igalia.com>
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Martin Robinson 2025-05-21 18:38:29 +02:00 • committed by GitHub
parent cebb1619ae
commit 9781f1241a
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23 changed files with 152 additions and 142 deletions
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20
components/layout/lib.rs
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@ -41,7 +41,6 @@ use malloc_size_of_derive::MallocSizeOf;
use servo_arc::Arc as ServoArc;
use style::logical_geometry::WritingMode;
use style::properties::ComputedValues;
use style::values::computed::TextDecorationLine;
use crate::geom::{LogicalVec2, SizeConstraint};
use crate::style_ext::AspectRatio;
@ -163,39 +162,20 @@ impl<'a> From<&'_ DefiniteContainingBlock<'a>> for ContainingBlock<'a> {
/// propoagation, but only during `BoxTree` construction.
#[derive(Clone, Copy, Debug)]
struct PropagatedBoxTreeData {
text_decoration: TextDecorationLine,
allow_percentage_column_in_tables: bool,
}
impl Default for PropagatedBoxTreeData {
fn default() -> Self {
Self {
text_decoration: Default::default(),
allow_percentage_column_in_tables: true,
}
}
}
impl PropagatedBoxTreeData {
pub(crate) fn union(&self, style: &ComputedValues) -> Self {
Self {
// FIXME(#31736): This is only taking into account the line style and not the decoration
// color. This should collect information about both so that they can be rendered properly.
text_decoration: self.text_decoration | style.clone_text_decoration_line(),
allow_percentage_column_in_tables: self.allow_percentage_column_in_tables,
}
}
pub(crate) fn without_text_decorations(&self) -> Self {
Self {
text_decoration: TextDecorationLine::NONE,
allow_percentage_column_in_tables: self.allow_percentage_column_in_tables,
}
}
fn disallowing_percentage_table_columns(&self) -> PropagatedBoxTreeData {
Self {
text_decoration: self.text_decoration,
allow_percentage_column_in_tables: false,
}
}