Backed out changeset 7e9751c1302a (bug 1022612)

layout/base/nsDisplayList.cpp

@@ -513,6 +513,7 @@ nsDisplayListBuilder::nsDisplayListBuilder(nsIFrame* aReferenceFrame,
       mAllowMergingAndFlattening(true),
       mWillComputePluginGeometry(false),
       mInTransform(false),
+      mInFixedPos(false),
       mSyncDecodeImages(false),
       mIsPaintingToWindow(false),
       mIsCompositingCheap(false),

layout/base/nsDisplayList.h

@@ -406,6 +406,12 @@ public:
    */
   void SetInTransform(bool aInTransform) { mInTransform = aInTransform; }
 
+  /**
+   * Returns true if we're currently building display items that are in
+   * true fixed position subtree.
+   */
+  bool IsInFixedPos() const { return mInFixedPos; }
+
   /**
    * @return true if images have been set to decode synchronously.
    */
@@ -592,6 +598,25 @@ public:
     bool                  mOldValue;
   };
 
+  /**
+   * A helper class to temporarily set the value of mInFixedPos.
+   */
+  class AutoInFixedPosSetter;
+  friend class AutoInFixedPosSetter;
+  class AutoInFixedPosSetter {
+  public:
+    AutoInFixedPosSetter(nsDisplayListBuilder* aBuilder, bool aInFixedPos)
+      : mBuilder(aBuilder), mOldValue(aBuilder->mInFixedPos) {
+      aBuilder->mInFixedPos = aInFixedPos;
+    }
+    ~AutoInFixedPosSetter() {
+      mBuilder->mInFixedPos = mOldValue;
+    }
+  private:
+    nsDisplayListBuilder* mBuilder;
+    bool                  mOldValue;
+  };
+
   /**
    * A helper class to temporarily set the value of mCurrentScrollParentId.
    */
@@ -765,6 +790,7 @@ private:
   // True when we're building a display list that's directly or indirectly
   // under an nsDisplayTransform
   bool                           mInTransform;
+  bool                           mInFixedPos;
   bool                           mSyncDecodeImages;
   bool                           mIsPaintingToWindow;
   bool                           mIsCompositingCheap;
@@ -822,6 +848,7 @@ public:
   nsDisplayItem(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame)
     : mFrame(aFrame)
     , mClip(aBuilder->ClipState().GetCurrentCombinedClip(aBuilder))
+    , mInFixedPos(aBuilder->IsInFixedPos())
 #ifdef MOZ_DUMP_PAINTING
     , mPainted(false)
 #endif
@@ -839,6 +866,7 @@ public:
     : mFrame(aFrame)
     , mClip(nullptr)
     , mReferenceFrame(nullptr)
+    , mInFixedPos(false)
 #ifdef MOZ_DUMP_PAINTING
     , mPainted(false)
 #endif
@@ -1332,6 +1360,8 @@ public:
     }
   }
 
+  bool IsInFixedPos() { return mInFixedPos; }
+
 protected:
   friend class nsDisplayList;
 
@@ -1349,6 +1379,7 @@ protected:
   // of the item. Paint implementations can use this to limit their drawing.
   // Guaranteed to be contained in GetBounds().
   nsRect    mVisibleRect;
+  bool      mInFixedPos;
 #ifdef MOZ_DUMP_PAINTING
   // True if this frame has been painted.
   bool      mPainted;

layout/generic/nsFrame.cpp

@@ -2290,6 +2290,13 @@ nsIFrame::BuildDisplayListForChild(nsDisplayListBuilder*   aBuilder,
   NS_ASSERTION(!isStackingContext || pseudoStackingContext,
                "Stacking contexts must also be pseudo-stacking-contexts");
 
+  bool isInFixedPos = aBuilder->IsInFixedPos() ||
+                        (isPositioned &&
+                         disp->mPosition == NS_STYLE_POSITION_FIXED &&
+                         nsLayoutUtils::IsReallyFixedPos(child));
+  nsDisplayListBuilder::AutoInFixedPosSetter
+    buildingInFixedPos(aBuilder, isInFixedPos);
+
   nsDisplayListBuilder::AutoBuildingDisplayList
     buildingForChild(aBuilder, child, dirty, pseudoStackingContext);
   DisplayListClipState::AutoClipMultiple clipState(aBuilder);

layout/generic/nsSubDocumentFrame.cpp

@@ -444,6 +444,13 @@ nsSubDocumentFrame::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
     haveDisplayPort ||
     presContext->IsRootContentDocument() || (sf && sf->IsScrollingActive());
 
+  // Don't let in fixed pos propagate down to child documents. This makes
+  // it a little less effective but doesn't regress an important case of a
+  // child document being in a fixed pos element where we would do no occlusion
+  // at all if we let it propagate down.
+  nsDisplayListBuilder::AutoInFixedPosSetter
+    buildingInFixedPos(aBuilder, false);
+
   nsDisplayList childItems;
 
   {