layout: Explicitly thread border box dimensions and relative offsets

through display list building.

The old `flow_origin` concept was ill-defined (sometimes the border box
plus the flow origin, sometimes including horizontal margins and
sometimes not, sometimes including relative position and sometimes not),
leading to brittleness and test failures. This commit reworks the logic
to always pass border box origins in during display list building.

1 files changed, 9 insertions, 18 deletions

diff --git a/components/layout/flow.rs b/components/layout/flow.rs
index f20d5a0c128..d252a93269b 100644
--- a/components/layout/flow.rs
+++ b/components/layout/flow.rs
@@ -32,7 +32,7 @@ use display_list_builder::DisplayListBuildingResult;
 use floats::Floats;
 use flow_list::{FlowList, FlowListIterator, MutFlowListIterator};
 use flow_ref::FlowRef;
-use fragment::{Fragment, FragmentOverflowIterator, SpecificFragmentInfo};
+use fragment::{Fragment, FragmentBorderBoxIterator, SpecificFragmentInfo};
 use incremental::{RECONSTRUCT_FLOW, REFLOW, REFLOW_OUT_OF_FLOW, RestyleDamage};
 use inline::InlineFlow;
 use model::{CollapsibleMargins, IntrinsicISizes, MarginCollapseInfo};
@@ -223,8 +223,10 @@ pub trait Flow: fmt::Show + ToString + Sync {
     /// Returns the union of all overflow rects of all of this flow's fragments.
     fn compute_overflow(&self) -> Rect<Au>;
 
-    /// Iterates through overflow rects of all of this flow's fragments.
-    fn iterate_through_fragment_overflow(&self, iterator: &mut FragmentOverflowIterator);
+    /// Iterates through border boxes of all of this flow's fragments.
+    fn iterate_through_fragment_border_boxes(&self,
+                                             iterator: &mut FragmentBorderBoxIterator,
+                                             stacking_context_position: &Point2D<Au>);
 
     fn compute_collapsible_block_start_margin(&mut self,
                                               _layout_context: &mut LayoutContext,
@@ -958,17 +960,6 @@ impl BaseFlow {
             }
         }
     }
-
-    /// Returns the position of the given fragment relative to the start of the nearest ancestor
-    /// stacking context. The fragment must be a child fragment of this flow.
-    pub fn stacking_relative_position_of_child_fragment(&self, fragment: &Fragment)
-                                                        -> Point2D<Au> {
-        let relative_offset =
-            fragment.relative_position(&self
-                                       .absolute_position_info
-                                       .relative_containing_block_size);
-        self.stacking_relative_position.add_size(&relative_offset.to_physical(self.writing_mode))
-    }
 }
 
 impl<'a> ImmutableFlowUtils for &'a Flow + 'a {
@@ -1065,14 +1056,14 @@ impl<'a> ImmutableFlowUtils for &'a Flow + 'a {
         let flow = match self.class() {
             FlowClass::Table | FlowClass::TableRowGroup => {
                 let fragment =
-                    Fragment::new_anonymous_table_fragment(node,
-                                                           SpecificFragmentInfo::TableRow);
+                    Fragment::new_anonymous_from_specific_info(node,
+                                                               SpecificFragmentInfo::TableRow);
                 box TableRowFlow::from_node_and_fragment(node, fragment) as Box<Flow>
             },
             FlowClass::TableRow => {
                 let fragment =
-                    Fragment::new_anonymous_table_fragment(node,
-                                                           SpecificFragmentInfo::TableCell);
+                    Fragment::new_anonymous_from_specific_info(node,
+                                                               SpecificFragmentInfo::TableCell);
                 let hide = node.style().get_inheritedtable().empty_cells == empty_cells::hide;
                 box TableCellFlow::from_node_fragment_and_visibility_flag(node, fragment, !hide) as
                     Box<Flow>