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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>
This commit is contained in:
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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87
components/layout/display_list/mod.rs
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@ -572,6 +572,7 @@ impl Fragment {
section: StackingContextSection,
is_hit_test_for_scrollable_overflow: bool,
is_collapsed_table_borders: bool,
text_decorations: &Arc<Vec<FragmentTextDecoration>>,
) {
let spatial_id = builder.spatial_id(builder.current_scroll_node_id);
let clip_chain_id = builder.clip_chain_id(builder.current_clip_id);
@ -683,9 +684,12 @@ impl Fragment {
.get_inherited_box()
.visibility
{
Visibility::Visible => {
self.build_display_list_for_text_fragment(text, builder, containing_block)
},
Visibility::Visible => self.build_display_list_for_text_fragment(
text,
builder,
containing_block,
text_decorations,
),
Visibility::Hidden => (),
Visibility::Collapse => (),
}
@ -723,6 +727,7 @@ impl Fragment {
fragment: &TextFragment,
builder: &mut DisplayListBuilder,
containing_block: &PhysicalRect<Au>,
text_decorations: &Arc<Vec<FragmentTextDecoration>>,
) {
// NB: The order of painting text components (CSS Text Decoration Module Level 3) is:
// shadows, underline, overline, text, text-emphasis, and then line-through.
@ -774,23 +779,33 @@ impl Fragment {
);
}
if fragment
.text_decoration_line
.contains(TextDecorationLine::UNDERLINE)
{
let mut rect = rect;
rect.origin.y += font_metrics.ascent - font_metrics.underline_offset;
rect.size.height = Au::from_f32_px(font_metrics.underline_size.to_nearest_pixel(dppx));
self.build_display_list_for_text_decoration(&parent_style, builder, &rect, &color);
for text_decoration in text_decorations.iter() {
if text_decoration.line.contains(TextDecorationLine::UNDERLINE) {
let mut rect = rect;
rect.origin.y += font_metrics.ascent - font_metrics.underline_offset;
rect.size.height =
Au::from_f32_px(font_metrics.underline_size.to_nearest_pixel(dppx));
self.build_display_list_for_text_decoration(
&parent_style,
builder,
&rect,
text_decoration,
);
}
}
if fragment
.text_decoration_line
.contains(TextDecorationLine::OVERLINE)
{
let mut rect = rect;
rect.size.height = Au::from_f32_px(font_metrics.underline_size.to_nearest_pixel(dppx));
self.build_display_list_for_text_decoration(&parent_style, builder, &rect, &color);
for text_decoration in text_decorations.iter() {
if text_decoration.line.contains(TextDecorationLine::OVERLINE) {
let mut rect = rect;
rect.size.height =
Au::from_f32_px(font_metrics.underline_size.to_nearest_pixel(dppx));
self.build_display_list_for_text_decoration(
&parent_style,
builder,
&rect,
text_decoration,
);
}
}
// TODO: This caret/text selection implementation currently does not account for vertical text
@ -867,14 +882,22 @@ impl Fragment {
None,
);
if fragment
.text_decoration_line
.contains(TextDecorationLine::LINE_THROUGH)
{
let mut rect = rect;
rect.origin.y += font_metrics.ascent - font_metrics.strikeout_offset;
rect.size.height = Au::from_f32_px(font_metrics.strikeout_size.to_nearest_pixel(dppx));
self.build_display_list_for_text_decoration(&parent_style, builder, &rect, &color);
for text_decoration in text_decorations.iter() {
if text_decoration
.line
.contains(TextDecorationLine::LINE_THROUGH)
{
let mut rect = rect;
rect.origin.y += font_metrics.ascent - font_metrics.strikeout_offset;
rect.size.height =
Au::from_f32_px(font_metrics.strikeout_size.to_nearest_pixel(dppx));
self.build_display_list_for_text_decoration(
&parent_style,
builder,
&rect,
text_decoration,
);
}
}
if !shadows.0.is_empty() {
@ -887,15 +910,11 @@ impl Fragment {
parent_style: &ServoArc<ComputedValues>,
builder: &mut DisplayListBuilder,
rect: &PhysicalRect<Au>,
color: &AbsoluteColor,
text_decoration: &FragmentTextDecoration,
) {
let rect = rect.to_webrender();
let wavy_line_thickness = (0.33 * rect.size().height).ceil();
let text_decoration_color = parent_style
.clone_text_decoration_color()
.resolve_to_absolute(color);
let text_decoration_style = parent_style.clone_text_decoration_style();
if text_decoration_style == ComputedTextDecorationStyle::MozNone {
if text_decoration.style == ComputedTextDecorationStyle::MozNone {
return;
}
let common_properties = builder.common_properties(rect, parent_style);
@ -904,8 +923,8 @@ impl Fragment {
&rect,
wavy_line_thickness,
wr::LineOrientation::Horizontal,
&rgba(text_decoration_color),
text_decoration_style.to_webrender(),
&rgba(text_decoration.color),
text_decoration.style.to_webrender(),
);
// XXX(ferjm) support text-decoration-style: double
}