From 48517bd61a07c0fe3ff5fbbed15a30e3aa4d965e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Fernando=20Jim=C3=A9nez=20Moreno?= <ferjmoreno@gmail.com>
Date: Mon, 2 Mar 2020 18:00:40 +0100
Subject: [PATCH] Render text-decoration: underline on layout 2020

---
 components/layout_2020/display_list/mod.rs | 90 ++++++++++++++++------
 1 file changed, 65 insertions(+), 25 deletions(-)

diff --git a/components/layout_2020/display_list/mod.rs b/components/layout_2020/display_list/mod.rs
index 56c9e9610ce..30ff68e3e1a 100644
--- a/components/layout_2020/display_list/mod.rs
+++ b/components/layout_2020/display_list/mod.rs
@@ -4,7 +4,7 @@
 
 use crate::context::LayoutContext;
 use crate::display_list::conversions::ToWebRender;
-use crate::fragments::{BoxFragment, Fragment};
+use crate::fragments::{BoxFragment, Fragment, TextFragment};
 use crate::geom::{PhysicalPoint, PhysicalRect};
 use crate::replaced::IntrinsicSizes;
 use embedder_traits::Cursor;
@@ -80,30 +80,6 @@ impl Fragment {
             Fragment::Box(b) => BuilderForBoxFragment::new(b, containing_block).build(builder),
             Fragment::AbsoluteOrFixedPositioned(_) => {},
             Fragment::Anonymous(_) => {},
-            Fragment::Text(t) => {
-                builder.is_contentful = true;
-                let rect = t
-                    .rect
-                    .to_physical(t.parent_style.writing_mode, containing_block)
-                    .translate(containing_block.origin.to_vector());
-                let mut baseline_origin = rect.origin.clone();
-                baseline_origin.y += t.font_metrics.ascent;
-                let glyphs = glyphs(&t.glyphs, baseline_origin);
-                if glyphs.is_empty() {
-                    return;
-                }
-                let mut common = builder.common_properties(rect.clone().to_webrender());
-                common.hit_info = hit_info(&t.parent_style, t.tag, Cursor::Text);
-                let color = t.parent_style.clone_color();
-                builder.wr.push_text(
-                    &common,
-                    rect.to_webrender(),
-                    &glyphs,
-                    t.font_key,
-                    rgba(color),
-                    None,
-                );
-            },
             Fragment::Image(i) => {
                 builder.is_contentful = true;
                 let rect = i
@@ -120,8 +96,72 @@ impl Fragment {
                     wr::ColorF::WHITE,
                 );
             },
+            Fragment::Text(t) => {
+                self.build_display_list_for_text_fragment(t, builder, containing_block)
+            },
         }
     }
+
+    fn build_display_list_for_text_fragment(
+        &self,
+        fragment: &TextFragment,
+        builder: &mut DisplayListBuilder,
+        containing_block: &PhysicalRect<Length>,
+    ) {
+        // NB: The order of painting text components (CSS Text Decoration Module Level 3) is:
+        // shadows, underline, overline, text, text-emphasis, and then line-through.
+
+        builder.is_contentful = true;
+
+        let rect = fragment
+            .rect
+            .to_physical(fragment.parent_style.writing_mode, containing_block)
+            .translate(containing_block.origin.to_vector());
+        let mut baseline_origin = rect.origin.clone();
+        baseline_origin.y += fragment.font_metrics.ascent;
+        let glyphs = glyphs(&fragment.glyphs, baseline_origin);
+        if glyphs.is_empty() {
+            return;
+        }
+
+        let mut common = builder.common_properties(rect.clone().to_webrender());
+        common.hit_info = hit_info(&fragment.parent_style, fragment.tag, Cursor::Text);
+
+        let color = fragment.parent_style.clone_color();
+
+        let text_decorations = fragment
+            .parent_style
+            .get_inherited_text()
+            .text_decorations_in_effect;
+        let font_metrics = &fragment.font_metrics;
+
+        // Underline.
+        if text_decorations.underline {
+            let mut rect = rect;
+            rect.origin.y = rect.origin.y + font_metrics.ascent - font_metrics.underline_offset;
+            rect.size.height = font_metrics.underline_size;
+            let rect = rect.to_webrender();
+            let wavy_line_thickness = (0.33 * rect.size.height).ceil();
+            builder.wr.push_line(
+                &common,
+                &rect,
+                wavy_line_thickness,
+                wr::LineOrientation::Horizontal,
+                &rgba(color),
+                wr::LineStyle::Solid,
+            );
+        }
+
+        // Text.
+        builder.wr.push_text(
+            &common,
+            rect.to_webrender(),
+            &glyphs,
+            fragment.font_key,
+            rgba(color),
+            None,
+        );
+    }
 }
 
 struct BuilderForBoxFragment<'a> {