layout: Move overflow calculation to be a separate, sequential,

bottom-up pass.

Right now, the only reason that overflow calculation works is that we
rely on script inducing extra reflows that are sent for display. This
was preventing #10021 from landing.

This change regresses layout performance by about 1% in my tests.

Fixes #7797 properly.

components/layout/incremental.rs

@@ -16,27 +16,31 @@ bitflags! {
         #[doc = "Currently unused; need to decide how this propagates."]
         const REPAINT = 0x01,
 
+        #[doc = "Recompute the overflow regions (bounding box of object and all descendants)."]
+        #[doc = "Propagates down the flow tree because the computation is bottom-up."]
+        const STORE_OVERFLOW = 0x02,
+
         #[doc = "Recompute intrinsic inline_sizes (minimum and preferred)."]
         #[doc = "Propagates down the flow tree because the computation is"]
         #[doc = "bottom-up."]
-        const BUBBLE_ISIZES = 0x02,
+        const BUBBLE_ISIZES = 0x04,
 
         #[doc = "Recompute actual inline-sizes and block-sizes, only taking out-of-flow children \
                  into account. \
                  Propagates up the flow tree because the computation is top-down."]
-        const REFLOW_OUT_OF_FLOW = 0x04,
+        const REFLOW_OUT_OF_FLOW = 0x08,
 
         #[doc = "Recompute actual inline_sizes and block_sizes."]
         #[doc = "Propagates up the flow tree because the computation is"]
         #[doc = "top-down."]
-        const REFLOW = 0x08,
+        const REFLOW = 0x10,
 
         #[doc = "Re-resolve generated content. \
                  Propagates up the flow tree because the computation is inorder."]
-        const RESOLVE_GENERATED_CONTENT = 0x10,
+        const RESOLVE_GENERATED_CONTENT = 0x20,
 
         #[doc = "The entire flow needs to be reconstructed."]
-        const RECONSTRUCT_FLOW = 0x20
+        const RECONSTRUCT_FLOW = 0x40
     }
 }
 
@@ -56,7 +60,7 @@ impl TRestyleDamage for RestyleDamage {
     /// Use this instead of `RestyleDamage::all()` because `RestyleDamage::all()` will result in
     /// unnecessary sequential resolution of generated content.
     fn rebuild_and_reflow() -> RestyleDamage {
-        REPAINT | BUBBLE_ISIZES | REFLOW_OUT_OF_FLOW | REFLOW | RECONSTRUCT_FLOW
+        REPAINT | STORE_OVERFLOW | BUBBLE_ISIZES | REFLOW_OUT_OF_FLOW | REFLOW | RECONSTRUCT_FLOW
     }
 }
 
@@ -66,9 +70,10 @@ impl RestyleDamage {
     /// we should add to the *parent* of this flow.
     pub fn damage_for_parent(self, child_is_absolutely_positioned: bool) -> RestyleDamage {
         if child_is_absolutely_positioned {
-            self & (REPAINT | REFLOW_OUT_OF_FLOW | RESOLVE_GENERATED_CONTENT)
+            self & (REPAINT | STORE_OVERFLOW | REFLOW_OUT_OF_FLOW | RESOLVE_GENERATED_CONTENT)
         } else {
-            self & (REPAINT | REFLOW | REFLOW_OUT_OF_FLOW | RESOLVE_GENERATED_CONTENT)
+            self & (REPAINT | STORE_OVERFLOW | REFLOW | REFLOW_OUT_OF_FLOW |
+                    RESOLVE_GENERATED_CONTENT)
         }
     }
 
@@ -108,6 +113,7 @@ impl fmt::Display for RestyleDamage {
 
         let to_iter =
             [ (REPAINT, "Repaint")
+            , (STORE_OVERFLOW, "StoreOverflow")
             , (BUBBLE_ISIZES, "BubbleISizes")
             , (REFLOW_OUT_OF_FLOW, "ReflowOutOfFlow")
             , (REFLOW, "Reflow")
@@ -165,13 +171,13 @@ pub fn compute_damage(old: Option<&Arc<ComputedValues>>, new: &ComputedValues) -
     ]);
 
     add_if_not_equal!(old, new, damage,
-                      [ REPAINT, REFLOW_OUT_OF_FLOW ], [
+                      [ REPAINT, STORE_OVERFLOW, REFLOW_OUT_OF_FLOW ], [
         get_positionoffsets.top, get_positionoffsets.left,
         get_positionoffsets.right, get_positionoffsets.bottom
     ]);
 
     add_if_not_equal!(old, new, damage,
-                      [ REPAINT, BUBBLE_ISIZES, REFLOW_OUT_OF_FLOW, REFLOW ], [
+                      [ REPAINT, STORE_OVERFLOW, BUBBLE_ISIZES, REFLOW_OUT_OF_FLOW, REFLOW ], [
         get_border.border_top_width, get_border.border_right_width,
         get_border.border_bottom_width, get_border.border_left_width,
         get_margin.margin_top, get_margin.margin_right,
@@ -183,7 +189,14 @@ pub fn compute_damage(old: Option<&Arc<ComputedValues>>, new: &ComputedValues) -
     ]);
 
     add_if_not_equal!(old, new, damage,
-                      [ REPAINT, BUBBLE_ISIZES, REFLOW_OUT_OF_FLOW, REFLOW, RECONSTRUCT_FLOW ], [
+                      [
+                        REPAINT,
+                        STORE_OVERFLOW,
+                        BUBBLE_ISIZES,
+                        REFLOW_OUT_OF_FLOW,
+                        REFLOW,
+                        RECONSTRUCT_FLOW
+                      ], [
         get_box.float, get_box.display, get_box.position, get_box.content,
         get_counters.counter_reset, get_counters.counter_increment,
         get_list.quotes, get_list.list_style_type,

components/layout/layout_thread.rs

@@ -12,7 +12,7 @@ use app_units::Au;
 use azure::azure::AzColor;
 use canvas_traits::CanvasMsg;
 use construct::ConstructionResult;
-use context::{SharedLayoutContext, heap_size_of_local_context};
+use context::{LayoutContext, SharedLayoutContext, heap_size_of_local_context};
 use display_list_builder::ToGfxColor;
 use euclid::Matrix4;
 use euclid::point::Point2D;
@@ -1336,14 +1336,23 @@ impl LayoutThread {
                     Some(ref mut parallel) => {
                         // Parallel mode.
                         LayoutThread::solve_constraints_parallel(parallel,
-                                                               &mut root_flow,
+                                                                 &mut root_flow,
-                                                               profiler_metadata,
+                                                                 profiler_metadata,
-                                                               self.time_profiler_chan.clone(),
+                                                                 self.time_profiler_chan.clone(),
-                                                               &*layout_context);
+                                                                 &*layout_context);
                     }
                 }
             });
 
+            profile(time::ProfilerCategory::LayoutStoreOverflow,
+                    self.profiler_metadata(),
+                    self.time_profiler_chan.clone(),
+                    || {
+                let layout_context = LayoutContext::new(&*layout_context);
+                sequential::store_overflow(&layout_context,
+                                           flow_ref::deref_mut(&mut root_flow) as &mut Flow);
+            });
+
             self.perform_post_main_layout_passes(data, rw_data, layout_context);
         }
     }

components/layout/sequential.rs

@@ -14,6 +14,7 @@ use flow_ref::{self, FlowRef};
 use fragment::FragmentBorderBoxIterator;
 use generated_content::ResolveGeneratedContent;
 use gfx::display_list::{DisplayListEntry, StackingContext};
+use incremental::STORE_OVERFLOW;
 use style::dom::TNode;
 use style::traversal::DomTraversalContext;
 use traversal::{AssignBSizes, AssignISizes};
@@ -117,3 +118,18 @@ pub fn iterate_through_flow_tree_fragment_border_boxes(root: &mut FlowRef,
 
     doit(flow_ref::deref_mut(root), 0, iterator, &Point2D::zero());
 }
+
+pub fn store_overflow(layout_context: &LayoutContext, flow: &mut Flow) {
+    if !flow::base(flow).restyle_damage.contains(STORE_OVERFLOW) {
+        return
+    }
+
+    for mut kid in flow::mut_base(flow).child_iter() {
+        store_overflow(layout_context, kid);
+    }
+
+    flow.store_overflow(layout_context);
+
+    flow::mut_base(flow).restyle_damage.remove(STORE_OVERFLOW);
+}
+

components/layout/traversal.rs

@@ -210,7 +210,6 @@ impl<'a> PreorderFlowTraversal for ComputeAbsolutePositions<'a> {
     #[inline]
     fn process(&self, flow: &mut Flow) {
         flow.compute_absolute_position(self.layout_context);
-        flow.store_overflow(self.layout_context);
     }
 }
 

components/profile/time.rs

@@ -60,6 +60,7 @@ impl Formattable for ProfilerCategory {
             ProfilerCategory::LayoutGeneratedContent |
             ProfilerCategory::LayoutDisplayListSorting |
             ProfilerCategory::LayoutMain |
+            ProfilerCategory::LayoutStoreOverflow |
             ProfilerCategory::LayoutDispListBuild |
             ProfilerCategory::LayoutDamagePropagate |
             ProfilerCategory::PaintingPerTile |
@@ -83,6 +84,7 @@ impl Formattable for ProfilerCategory {
             ProfilerCategory::LayoutDisplayListSorting => "Sorting Display List",
             ProfilerCategory::LayoutGeneratedContent => "Generated Content Resolution",
             ProfilerCategory::LayoutMain => "Primary Layout Pass",
+            ProfilerCategory::LayoutStoreOverflow => "Store Overflow",
             ProfilerCategory::LayoutParallelWarmup => "Parallel Warmup",
             ProfilerCategory::LayoutDispListBuild => "Display List Construction",
             ProfilerCategory::PaintingPerTile => "Painting Per Tile",

components/profile_traits/time.rs

@@ -50,6 +50,7 @@ pub enum ProfilerCategory {
     LayoutGeneratedContent,
     LayoutDisplayListSorting,
     LayoutMain,
+    LayoutStoreOverflow,
     LayoutParallelWarmup,
     LayoutDispListBuild,
     PaintingPerTile,

tests/wpt/metadata-css/css21_dev/html4/numbers-units-018.htm.ini

@@ -0,0 +1,3 @@
+[numbers-units-018.htm]
+  type: reftest
+  expected: FAIL