layout: Stop going to the DOM for text alignment.

Verified against the existing text alignment reftests.

src/components/main/layout/block.rs

@@ -585,11 +585,13 @@ impl Flow for BlockFlow {
     /// Dual boxes consume some width first, and the remainder is assigned to all child (block)
     /// contexts.
     fn assign_widths(&mut self, ctx: &mut LayoutContext) {
-        if self.is_float() {
-            debug!("assign_widths_float: assigning width for flow {}",  self.base.id);
-        } else {
-            debug!("assign_widths_block: assigning width for flow {}",  self.base.id);
-        }
+        debug!("assign_widths({}): assigning width for flow {}",
+               if self.is_float() {
+                   "float"
+               } else {
+                   "block"
+               },
+               self.base.id);
 
         if self.is_root {
             debug!("Setting root position");
@@ -613,6 +615,9 @@ impl Flow for BlockFlow {
         for box in self.box.iter() {
             let style = box.style();
 
+            // The text alignment of a block flow is the text alignment of its box's style.
+            self.base.flags.set_text_align(style.Text.text_align);
+
             // Can compute padding here since we know containing block width.
             box.compute_padding(style, remaining_width);
 
@@ -672,7 +677,9 @@ impl Flow for BlockFlow {
             // Per CSS 2.1 § 16.3.1, text decoration propagates to all children in flow.
             //
             // TODO(pcwalton): When we have out-of-flow children, don't unconditionally propagate.
-            child_base.flags.propagate_text_decoration_from_parent(self.base.flags)
+            child_base.flags.propagate_text_decoration_from_parent(self.base.flags);
+
+            child_base.flags.propagate_text_alignment_from_parent(self.base.flags)
         }
     }
 

src/components/main/layout/flow.rs

@@ -44,6 +44,7 @@ use servo_util::geometry::Au;
 use std::cast;
 use std::cell::Cell;
 use style::ComputedValues;
+use style::computed_values::text_align;
 
 /// Virtual methods that make up a float context.
 ///
@@ -313,6 +314,16 @@ pub struct FlowFlags(u8);
 /// NB: If you update this field, you must update the bitfields below.
 static TEXT_DECORATION_OVERRIDE_BITMASK: u8 = 0b00001110;
 
+/// The bitmask of flags that represent the text alignment field.
+///
+/// NB: If you update this field, you must update the bitfields below.
+static TEXT_ALIGN_BITMASK: u8 = 0b00110000;
+
+/// The number of bits we must shift off to handle the text alignment field.
+///
+/// NB: If you update this field, you must update the bitfields below.
+static TEXT_ALIGN_SHIFT: u8 = 4;
+
 impl FlowFlags {
     /// Creates a new set of flow flags from the given style.
     fn new(style: &ComputedValues) -> FlowFlags {
@@ -328,6 +339,11 @@ impl FlowFlags {
     pub fn propagate_text_decoration_from_parent(&mut self, parent: FlowFlags) {
         *self = FlowFlags(**self | (*parent & TEXT_DECORATION_OVERRIDE_BITMASK))
     }
+
+    /// Propagates text alignment flags from an appropriate parent flow per CSS 2.1.
+    pub fn propagate_text_alignment_from_parent(&mut self, parent: FlowFlags) {
+        *self = FlowFlags(**self | (*parent & TEXT_ALIGN_BITMASK))
+    }
 }
 
 // Whether we need an in-order traversal.
@@ -348,6 +364,19 @@ bitfield!(FlowFlags, override_overline, set_override_overline, 0x04)
 // NB: If you update this, you need to update TEXT_DECORATION_OVERRIDE_BITMASK.
 bitfield!(FlowFlags, override_line_through, set_override_line_through, 0x08)
 
+// The text alignment for this flow.
+impl FlowFlags {
+    #[inline]
+    pub fn text_align(self) -> text_align::T {
+        FromPrimitive::from_u8((*self & TEXT_ALIGN_BITMASK) >> TEXT_ALIGN_SHIFT).unwrap()
+    }
+
+    #[inline]
+    pub fn set_text_align(&mut self, value: text_align::T) {
+        *self = FlowFlags((**self & !TEXT_ALIGN_BITMASK) | ((value as u8) << TEXT_ALIGN_SHIFT))
+    }
+}
+
 /// Data common to all flows.
 ///
 /// FIXME: We need a naming convention for pseudo-inheritance like this. How about

src/components/main/layout/inline.rs

@@ -17,13 +17,13 @@ use extra::container::Deque;
 use extra::ringbuf::RingBuf;
 use geom::{Point2D, Rect, Size2D};
 use gfx::display_list::DisplayList;
-use style::computed_values::text_align;
-use style::computed_values::vertical_align;
 use servo_util::geometry::Au;
 use servo_util::range::Range;
 use std::cell::Cell;
 use std::u16;
 use std::util;
+use style::computed_values::text_align;
+use style::computed_values::vertical_align;
 
 /// Lineboxes are represented as offsets into the child list, rather than
 /// as an object that "owns" boxes. Choosing a different set of line
@@ -644,7 +644,8 @@ impl Flow for InlineFlow {
         //
         // TODO: Combine this with `LineboxScanner`'s walk in the box list, or put this into `Box`.
 
-        debug!("assign_widths_inline: floats_in: {:?}", self.base.floats_in);
+        debug!("InlineFlow::assign_widths: floats_in: {:?}", self.base.floats_in);
+
         {
             let this = &mut *self;
             for box in this.boxes.iter() {
@@ -656,6 +657,7 @@ impl Flow for InlineFlow {
             let child_base = flow::mut_base(*kid);
             child_base.position.size.width = self.base.position.size.width;
             child_base.flags.set_inorder(self.base.flags.inorder());
+            child_base.flags.propagate_text_alignment_from_parent(self.base.flags)
         }
         // There are no child contexts, so stop here.
 
@@ -695,8 +697,8 @@ impl Flow for InlineFlow {
 
         let mut line_height_offset = Au::new(0);
 
-        // All lines use text alignment from base (non-inline) node
-        let text_align = self.base.node.style().get().Text.text_align;
+        // All lines use text alignment of the flow.
+        let text_align = self.base.flags.text_align();
 
         // Now, go through each line and lay out the boxes inside.
         for line in self.lines.mut_iter() {

src/components/style/properties.rs.mako

@@ -106,7 +106,7 @@ pub mod longhands {
         <%self:single_component_value name="${name}" inherited="${inherited}">
             ${caller.body()}
             pub mod computed_value {
-                #[deriving(Eq, Clone)]
+                #[deriving(Eq, Clone, FromPrimitive)]
                 pub enum T {
                     % for value in values.split():
                         ${to_rust_ident(value)},