From a438107cde7ab7d366815633f8ff5c46eef8c038 Mon Sep 17 00:00:00 2001
From: Robert O'Callahan <robert@ocallahan.org>
Date: Mon, 9 Jun 2014 16:48:02 +1200
Subject: [PATCH] Bug 1022612. Part 24: Simplify
 nsDisplayList::ComputeVisibilityForSublist now that FrameLayerBuilder does
 most of the work. r=mattwoodrow

--HG--
extra : rebase_source : 0db68211898c111a465dc641bed8e3b2923f0e4e
---
 layout/base/nsDisplayList.cpp | 79 +++--------------------------------
 layout/base/nsDisplayList.h   |  3 --
 2 files changed, 5 insertions(+), 77 deletions(-)

diff --git a/layout/base/nsDisplayList.cpp b/layout/base/nsDisplayList.cpp
index 7bf5abf89e14..60aae868fc44 100644
--- a/layout/base/nsDisplayList.cpp
+++ b/layout/base/nsDisplayList.cpp
@@ -1017,16 +1017,11 @@ void nsDisplayListSet::MoveTo(const nsDisplayListSet& aDestination) const
   aDestination.Outlines()->AppendToTop(Outlines());
 }
 
-void
-nsDisplayList::FlattenTo(nsTArray<nsDisplayItem*>* aElements) {
+static void
+MoveListTo(nsDisplayList* aList, nsTArray<nsDisplayItem*>* aElements) {
   nsDisplayItem* item;
-  while ((item = RemoveBottom()) != nullptr) {
-    if (item->GetType() == nsDisplayItem::TYPE_WRAP_LIST) {
-      item->GetSameCoordinateSystemChildren()->FlattenTo(aElements);
-      item->~nsDisplayItem();
-    } else {
-      aElements->AppendElement(item);
-    }
+  while ((item = aList->RemoveBottom()) != nullptr) {
+    aElements->AppendElement(item);
   }
 }
 
@@ -1094,31 +1089,6 @@ TreatAsOpaque(nsDisplayItem* aItem, nsDisplayListBuilder* aBuilder)
   return opaqueClipped;
 }
 
-/* Checks if aPotentialScrollItem is a scroll layer item and aPotentialScrollbarItem
- * is an overlay scrollbar item for the same scroll frame.
- */
-static bool
-IsScrollLayerItemAndOverlayScrollbarForScrollFrame(
-  nsDisplayItem* aPotentialScrollItem, nsDisplayItem* aPotentialScrollbarItem)
-{
-  if (aPotentialScrollItem->GetType() == nsDisplayItem::TYPE_SCROLL_LAYER &&
-      aPotentialScrollbarItem &&
-      aPotentialScrollbarItem->GetType() == nsDisplayItem::TYPE_OWN_LAYER &&
-      LookAndFeel::GetInt(LookAndFeel::eIntID_UseOverlayScrollbars)) {
-    nsDisplayScrollLayer* scrollItem =
-      static_cast<nsDisplayScrollLayer*>(aPotentialScrollItem);
-    nsDisplayOwnLayer* layerItem =
-      static_cast<nsDisplayOwnLayer*>(aPotentialScrollbarItem);
-    if ((layerItem->GetFlags() &
-         (nsDisplayOwnLayer::VERTICAL_SCROLLBAR |
-          nsDisplayOwnLayer::HORIZONTAL_SCROLLBAR)) &&
-        layerItem->Frame()->GetParent() == scrollItem->GetScrollFrame()) {
-      return true;
-    }
-  }
-  return false;
-}
-
 bool
 nsDisplayList::ComputeVisibilityForSublist(nsDisplayListBuilder* aBuilder,
                                            nsRegion* aVisibleRegion,
@@ -1136,43 +1106,10 @@ nsDisplayList::ComputeVisibilityForSublist(nsDisplayListBuilder* aBuilder,
   bool anyVisible = false;
 
   nsAutoTArray<nsDisplayItem*, 512> elements;
-  FlattenTo(&elements);
-
-  bool forceTransparentSurface = false;
+  MoveListTo(this, &elements);
 
   for (int32_t i = elements.Length() - 1; i >= 0; --i) {
     nsDisplayItem* item = elements[i];
-    nsDisplayItem* belowItem = i < 1 ? nullptr : elements[i - 1];
-
-    nsDisplayList* list = item->GetSameCoordinateSystemChildren();
-    if (aBuilder->AllowMergingAndFlattening()) {
-      if (belowItem && item->TryMerge(aBuilder, belowItem)) {
-        belowItem->~nsDisplayItem();
-        elements.ReplaceElementsAt(i - 1, 1, item);
-        continue;
-      }
-
-      // If an overlay scrollbar item is between a scroll layer item and the
-      // other scroll layer items that we need to merge with just move the
-      // scrollbar item up, that way it will be on top of the scrolled content
-      // and we can try to merge all the scroll layer items.
-      if (IsScrollLayerItemAndOverlayScrollbarForScrollFrame(item, belowItem)) {
-        elements[i] = belowItem;
-        elements[i-1] = item;
-        i++;
-        continue;
-      }
-
-      if (list && item->ShouldFlattenAway(aBuilder)) {
-        // The elements on the list >= i no longer serve any use.
-        elements.SetLength(i);
-        list->FlattenTo(&elements);
-        i = elements.Length();
-        item->~nsDisplayItem();
-        continue;
-      }
-    }
-
     nsRect bounds = item->GetClippedBounds(aBuilder);
 
     nsRegion itemVisible;
@@ -1216,17 +1153,11 @@ nsDisplayList::ComputeVisibilityForSublist(nsDisplayListBuilder* aBuilder,
           aVisibleRegion->SetEmpty();
         }
       }
-
-      if (aBuilder->NeedToForceTransparentSurfaceForItem(item) ||
-          (list && list->NeedsTransparentSurface())) {
-        forceTransparentSurface = true;
-      }
     }
     AppendToBottom(item);
   }
 
   mIsOpaque = !aVisibleRegion->Intersects(mVisibleRect);
-  mForceTransparentSurface = forceTransparentSurface;
   return anyVisible;
 }
 
diff --git a/layout/base/nsDisplayList.h b/layout/base/nsDisplayList.h
index 449566085f28..202ab118f88e 100644
--- a/layout/base/nsDisplayList.h
+++ b/layout/base/nsDisplayList.h
@@ -1699,9 +1699,6 @@ private:
   // it.  Don't let us be heap-allocated!
   void* operator new(size_t sz) CPP_THROW_NEW;
   
-  // Utility function used to massage the list during ComputeVisibility.
-  void FlattenTo(nsTArray<nsDisplayItem*>* aElements);
-  
   nsDisplayItemLink  mSentinel;
   nsDisplayItemLink* mTop;