From 7f0cebd44291ab73794b5b2f51fc9074684a8600 Mon Sep 17 00:00:00 2001
From: Martin Robinson <mrobinson@igalia.com>
Date: Thu, 22 May 2025 19:42:50 +0200
Subject: [PATCH] layout: Support `wavy` and `double` for
 `text-decoration-line` (#37079)

- Add support for `text-decoration-line: double`: Line drawing is done
similar to how it works in Firefox and Chromium. A gap of half of line
thickness is added between each line.
- Fix support for `text-decoration-line: wavy`: Wavy lines rectangles
were not calcualted properly, which meant they were rendered as solid
lines. Now the amplitude of the wave is 1.5 times line thickness.

Testing: A manual test is updated `tests/html/text_deco_simple.html`
to cover more cases. In general, rendering of text-decorations is
difficult
to test via reftesting.
Fixes #17887.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>
---
 components/layout/display_list/conversions.rs |  8 ++-
 components/layout/display_list/mod.rs         | 43 ++++++++++++---
 tests/html/text_deco_simple.html              | 53 ++++++++++++++-----
 3 files changed, 84 insertions(+), 20 deletions(-)

diff --git a/components/layout/display_list/conversions.rs b/components/layout/display_list/conversions.rs
index 6d78a17e886..a2517c863f1 100644
--- a/components/layout/display_list/conversions.rs
+++ b/components/layout/display_list/conversions.rs
@@ -125,11 +125,15 @@ impl ToWebRender for ComputedTextDecorationStyle {
     type Type = LineStyle;
     fn to_webrender(&self) -> Self::Type {
         match *self {
-            ComputedTextDecorationStyle::Solid => LineStyle::Solid,
+            ComputedTextDecorationStyle::Solid | ComputedTextDecorationStyle::Double => {
+                LineStyle::Solid
+            },
             ComputedTextDecorationStyle::Dotted => LineStyle::Dotted,
             ComputedTextDecorationStyle::Dashed => LineStyle::Dashed,
             ComputedTextDecorationStyle::Wavy => LineStyle::Wavy,
-            _ => LineStyle::Solid,
+            ComputedTextDecorationStyle::MozNone => {
+                unreachable!("Should never try to draw a moz-none text decoration")
+            },
         }
     }
 }
diff --git a/components/layout/display_list/mod.rs b/components/layout/display_list/mod.rs
index 58ec58c9ce2..3716ff35b2c 100644
--- a/components/layout/display_list/mod.rs
+++ b/components/layout/display_list/mod.rs
@@ -11,7 +11,7 @@ use base::id::ScrollTreeNodeId;
 use clip::{Clip, ClipId};
 use compositing_traits::display_list::{CompositorDisplayListInfo, SpatialTreeNodeInfo};
 use embedder_traits::Cursor;
-use euclid::{Point2D, SideOffsets2D, Size2D, UnknownUnit};
+use euclid::{Point2D, SideOffsets2D, Size2D, UnknownUnit, Vector2D};
 use fonts::GlyphStore;
 use gradient::WebRenderGradient;
 use range::Range as ServoRange;
@@ -21,7 +21,9 @@ use servo_geometry::MaxRect;
 use style::Zero;
 use style::color::{AbsoluteColor, ColorSpace};
 use style::computed_values::border_image_outset::T as BorderImageOutset;
-use style::computed_values::text_decoration_style::T as ComputedTextDecorationStyle;
+use style::computed_values::text_decoration_style::{
+    T as ComputedTextDecorationStyle, T as TextDecorationStyle,
+};
 use style::dom::OpaqueNode;
 use style::properties::ComputedValues;
 use style::properties::longhands::visibility::computed_value::T as Visibility;
@@ -737,6 +739,7 @@ impl Fragment {
         let rect = fragment.rect.translate(containing_block.origin.to_vector());
         let mut baseline_origin = rect.origin;
         baseline_origin.y += fragment.font_metrics.ascent;
+
         let glyphs = glyphs(
             &fragment.glyphs,
             baseline_origin,
@@ -785,11 +788,13 @@ impl Fragment {
                 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,
+                    TextDecorationLine::UNDERLINE,
                 );
             }
         }
@@ -804,6 +809,7 @@ impl Fragment {
                     builder,
                     &rect,
                     text_decoration,
+                    TextDecorationLine::OVERLINE,
                 );
             }
         }
@@ -896,6 +902,7 @@ impl Fragment {
                     builder,
                     &rect,
                     text_decoration,
+                    TextDecorationLine::LINE_THROUGH,
                 );
             }
         }
@@ -911,22 +918,46 @@ impl Fragment {
         builder: &mut DisplayListBuilder,
         rect: &PhysicalRect<Au>,
         text_decoration: &FragmentTextDecoration,
+        line: TextDecorationLine,
     ) {
-        let rect = rect.to_webrender();
-        let wavy_line_thickness = (0.33 * rect.size().height).ceil();
         if text_decoration.style == ComputedTextDecorationStyle::MozNone {
             return;
         }
+
+        let mut rect = rect.to_webrender();
+        let line_thickness = rect.height().ceil();
+
+        if text_decoration.style == ComputedTextDecorationStyle::Wavy {
+            rect = rect.inflate(0.0, line_thickness * 1.0);
+        }
+
         let common_properties = builder.common_properties(rect, parent_style);
         builder.wr().push_line(
             &common_properties,
             &rect,
-            wavy_line_thickness,
+            line_thickness,
             wr::LineOrientation::Horizontal,
             &rgba(text_decoration.color),
             text_decoration.style.to_webrender(),
         );
-        // XXX(ferjm) support text-decoration-style: double
+
+        if text_decoration.style == TextDecorationStyle::Double {
+            let half_height = (rect.height() / 2.0).floor().max(1.0);
+            let y_offset = match line {
+                TextDecorationLine::OVERLINE => -rect.height() - half_height,
+                _ => rect.height() + half_height,
+            };
+            let rect = rect.translate(Vector2D::new(0.0, y_offset));
+            let common_properties = builder.common_properties(rect, parent_style);
+            builder.wr().push_line(
+                &common_properties,
+                &rect,
+                line_thickness,
+                wr::LineOrientation::Horizontal,
+                &rgba(text_decoration.color),
+                text_decoration.style.to_webrender(),
+            );
+        }
     }
 }
 
diff --git a/tests/html/text_deco_simple.html b/tests/html/text_deco_simple.html
index 73d48199c96..52ced9aede0 100644
--- a/tests/html/text_deco_simple.html
+++ b/tests/html/text_deco_simple.html
@@ -1,17 +1,46 @@
 <!DOCTYPE html>
+
 <html>
-<head>
-<title></title>
-</head>
 <body>
-    <p style="text-decoration:none;"> none </p>
-    <p style="text-decoration:underline;"> text underline </p>
-    <p style="text-decoration:overline;"> text underline </p>
-    <p style="text-decoration:line-through;"> text underline </p>
-    <p>
-    <p style="font-size:40px; text-decoration:underline; font-family:Verdana;"> text underline pqrstg </p>
-    <p style="text-decoration:overline;"> text overline xxxxxxxxXXXXXXX</p>
-    <p style="font-size:50px; text-decoration:line-through;"> text line-through xxxxxxxxXXXXX</p>
-    <p style="text-decoration:blink;"> text blink </p>
+
+<style>
+    p {
+        font-family: "Times New Roman";
+        background: lightgrey;
+        padding: 5px;
+        margin: 5px;
+    }
+</style>
+
+<p style="text-decoration: none blue;">text-decoration: </p>
+<p style="text-decoration: underline blue;">text-decoration: </p>
+<p style="text-decoration: overline blue;">text-decoration: </p>
+<p style="text-decoration: line-through blue;">text-decoration: </p>
+
+<p style="text-decoration: underline double blue;">text-decoration: </p>
+<p style="text-decoration: overline double blue;">text-decoration: </p>
+<p style="text-decoration: line-through double blue;">text-decoration: </p>
+
+<p style="text-decoration: underline wavy blue;">text-decoration: </p>
+<p style="text-decoration: overline wavy blue;">text-decoration: </p>
+<p style="text-decoration: line-through wavy blue;">text-decoration: </p>
+
+<p style="text-decoration: underline dashed blue;">text-decoration: </p>
+<p style="text-decoration: overline dashed blue;">text-decoration: </p>
+<p style="text-decoration: line-through dashed blue;">text-decoration: </p>
+
+<p style="text-decoration: underline dotted blue;">text-decoration: </p>
+<p style="text-decoration: overline dotted blue;">text-decoration: </p>
+<p style="text-decoration: line-through dotted blue;">text-decoration: </p>
+
+<script>
+    for (paragraph of document.querySelectorAll("p")) {
+        paragraph.innerText += " " +
+            getComputedStyle(paragraph).textDecorationLine + " " +
+            getComputedStyle(paragraph).textDecorationStyle;
+
+    }
+</script>
+
 </body>
 </html>