layout: Perform text decoration propagation per CSS 2.1 § 16.3.1 without

going to the DOM.

src/components/gfx/display_list.rs

@@ -92,12 +92,38 @@ pub struct SolidColorDisplayItem<E> {
 
 /// Renders text.
 pub struct TextDisplayItem<E> {
+    /// Fields common to all display items.
     base: BaseDisplayItem<E>,
+
+    /// The text run.
     text_run: Arc<~TextRun>,
+
+    /// The range of text within the text run.
     range: Range,
+
+    /// The color of the text.
     color: Color,
+
+    /// A bitfield of flags for text display items.
+    flags: TextDisplayItemFlags,
 }
 
+/// Flags for text display items.
+pub struct TextDisplayItemFlags(u8);
+
+impl TextDisplayItemFlags {
+    pub fn new() -> TextDisplayItemFlags {
+        TextDisplayItemFlags(0)
+    }
+}
+
+// Whether underlining is forced on.
+bitfield!(TextDisplayItemFlags, override_underline, set_override_underline, 0x01)
+// Whether overlining is forced on.
+bitfield!(TextDisplayItemFlags, override_overline, set_override_overline, 0x02)
+// Whether line-through is forced on.
+bitfield!(TextDisplayItemFlags, override_line_through, set_override_line_through, 0x04)
+
 /// Renders an image.
 pub struct ImageDisplayItem<E> {
     base: BaseDisplayItem<E>,
@@ -184,18 +210,18 @@ impl<E> DisplayItem<E> {
                 let strikeout_size = font_metrics.strikeout_size;
                 let strikeout_offset = font_metrics.strikeout_offset;
 
-                if text_run.decoration.underline {
+                if text_run.decoration.underline || text.flags.override_underline() {
                     let underline_y = baseline_origin.y - underline_offset;
                     let underline_bounds = Rect(Point2D(baseline_origin.x, underline_y),
                                                 Size2D(width, underline_size));
                     render_context.draw_solid_color(&underline_bounds, text.color);
                 }
-                if text_run.decoration.overline {
+                if text_run.decoration.overline || text.flags.override_overline() {
                     let overline_bounds = Rect(Point2D(baseline_origin.x, origin.y),
                                                Size2D(width, underline_size));
                     render_context.draw_solid_color(&overline_bounds, text.color);
                 }
-                if text_run.decoration.line_through {
+                if text_run.decoration.line_through || text.flags.override_line_through() {
                     let strikeout_y = baseline_origin.y - strikeout_offset;
                     let strikeout_bounds = Rect(Point2D(baseline_origin.x, strikeout_y),
                                                 Size2D(width, strikeout_size));

src/components/gfx/gfx.rc

@@ -40,6 +40,10 @@ pub use gfx_font_list = font_list;
 pub use servo_gfx_font = font;
 pub use servo_gfx_font_list = font_list;
 
+// Macros
+mod macros;
+
+// Private rendering modules
 mod render_context;
 
 // Rendering

src/components/gfx/macros.rs

@@ -0,0 +1,22 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#[macro_escape];
+
+macro_rules! bitfield(
+    ($bitfieldname:ident, $getter:ident, $setter:ident, $value:expr) => (
+        impl $bitfieldname {
+            #[inline]
+            pub fn $getter(self) -> bool {
+                (*self & $value) != 0
+            }
+
+            #[inline]
+            pub fn $setter(&mut self, value: bool) {
+                *self = $bitfieldname((**self & !$value) | (if value { $value } else { 0 }))
+            }
+        }
+    )
+)
+