Bug 982888 - Populate the scroll parent field as appropriate. r=

layout/base/nsDisplayList.cpp

@@ -505,6 +505,7 @@ nsDisplayListBuilder::nsDisplayListBuilder(nsIFrame* aReferenceFrame,
       mCachedOffset(0, 0),
       mGlassDisplayItem(nullptr),
       mMode(aMode),
+      mCurrentScrollParentId(FrameMetrics::NULL_SCROLL_ID),
       mBuildCaret(aBuildCaret),
       mIgnoreSuppression(false),
       mHadToIgnoreSuppression(false),
@@ -3524,7 +3525,9 @@ nsDisplayOwnLayer::BuildLayer(nsDisplayListBuilder* aBuilder,
 nsDisplaySubDocument::nsDisplaySubDocument(nsDisplayListBuilder* aBuilder,
                                            nsIFrame* aFrame, nsDisplayList* aList,
                                            uint32_t aFlags)
-    : nsDisplayOwnLayer(aBuilder, aFrame, aList, aFlags) {
+    : nsDisplayOwnLayer(aBuilder, aFrame, aList, aFlags)
+    , mScrollParentId(aBuilder->GetCurrentScrollParentId())
+{
   MOZ_COUNT_CTOR(nsDisplaySubDocument);
 }
 
@@ -3574,6 +3577,7 @@ nsDisplaySubDocument::BuildLayer(nsDisplayListBuilder* aBuilder,
                       mFrame->GetPosition() +
                       mFrame->GetOffsetToCrossDoc(ReferenceFrame());
 
+    container->SetScrollHandoffParentId(mScrollParentId);
     RecordFrameMetrics(mFrame, rootScrollFrame, ReferenceFrame(),
                        container, mList.GetVisibleRect(), viewport,
                        (usingDisplayport ? &displayport : nullptr),
@@ -3779,6 +3783,7 @@ nsDisplayScrollLayer::nsDisplayScrollLayer(nsDisplayListBuilder* aBuilder,
   : nsDisplayWrapList(aBuilder, aForFrame, aList)
   , mScrollFrame(aScrollFrame)
   , mScrolledFrame(aScrolledFrame)
+  , mScrollParentId(aBuilder->GetCurrentScrollParentId())
 {
 #ifdef NS_BUILD_REFCNT_LOGGING
   MOZ_COUNT_CTOR(nsDisplayScrollLayer);
@@ -3796,6 +3801,7 @@ nsDisplayScrollLayer::nsDisplayScrollLayer(nsDisplayListBuilder* aBuilder,
   : nsDisplayWrapList(aBuilder, aForFrame, aItem)
   , mScrollFrame(aScrollFrame)
   , mScrolledFrame(aScrolledFrame)
+  , mScrollParentId(aBuilder->GetCurrentScrollParentId())
 {
 #ifdef NS_BUILD_REFCNT_LOGGING
   MOZ_COUNT_CTOR(nsDisplayScrollLayer);
@@ -3812,6 +3818,7 @@ nsDisplayScrollLayer::nsDisplayScrollLayer(nsDisplayListBuilder* aBuilder,
   : nsDisplayWrapList(aBuilder, aForFrame)
   , mScrollFrame(aScrollFrame)
   , mScrolledFrame(aScrolledFrame)
+  , mScrollParentId(aBuilder->GetCurrentScrollParentId())
 {
 #ifdef NS_BUILD_REFCNT_LOGGING
   MOZ_COUNT_CTOR(nsDisplayScrollLayer);
@@ -3864,6 +3871,7 @@ nsDisplayScrollLayer::BuildLayer(nsDisplayListBuilder* aBuilder,
     usingCriticalDisplayport =
       nsLayoutUtils::GetCriticalDisplayPort(content, &criticalDisplayport);
   }
+  layer->SetScrollHandoffParentId(mScrollParentId);
   RecordFrameMetrics(mScrolledFrame, mScrollFrame, ReferenceFrame(), layer,
                      mList.GetVisibleRect(), viewport,
                      (usingDisplayport ? &displayport : nullptr),

layout/base/nsDisplayList.h

@@ -114,6 +114,7 @@ public:
   typedef mozilla::DisplayListClipState DisplayListClipState;
   typedef nsIWidget::ThemeGeometry ThemeGeometry;
   typedef mozilla::layers::Layer Layer;
+  typedef mozilla::layers::FrameMetrics::ViewID ViewID;
 
   /**
    * @param aReferenceFrame the frame at the root of the subtree; its origin
@@ -248,6 +249,10 @@ public:
    * Get the scrollframe to ignore, if any.
    */
   nsIFrame* GetIgnoreScrollFrame() { return mIgnoreScrollFrame; }
+  /**
+   * Get the ViewID of the nearest scrolling ancestor frame.
+   */
+  ViewID GetCurrentScrollParentId() const { return mCurrentScrollParentId; }
   /**
    * Calling this setter makes us include all out-of-flow descendant
    * frames in the display list, wherever they may be positioned (even
@@ -602,6 +607,25 @@ public:
     bool                  mOldValue;
   };
 
+  /**
+   * A helper class to temporarily set the value of mCurrentScrollParentId.
+   */
+  class AutoCurrentScrollParentIdSetter;
+  friend class AutoCurrentScrollParentIdSetter;
+  class AutoCurrentScrollParentIdSetter {
+  public:
+    AutoCurrentScrollParentIdSetter(nsDisplayListBuilder* aBuilder, ViewID aScrollId)
+      : mBuilder(aBuilder), mOldValue(aBuilder->mCurrentScrollParentId) {
+      aBuilder->mCurrentScrollParentId = aScrollId;
+    }
+    ~AutoCurrentScrollParentIdSetter() {
+      mBuilder->mCurrentScrollParentId = mOldValue;
+    }
+  private:
+    nsDisplayListBuilder* mBuilder;
+    ViewID                mOldValue;
+  };
+
   // Helpers for tables
   nsDisplayTableItem* GetCurrentTableItem() { return mCurrentTableItem; }
   void SetCurrentTableItem(nsDisplayTableItem* aTableItem) { mCurrentTableItem = aTableItem; }
@@ -706,6 +730,7 @@ private:
   nsDisplayItem*                 mGlassDisplayItem;
   nsTArray<DisplayItemClip*>     mDisplayItemClipsToDestroy;
   Mode                           mMode;
+  ViewID                         mCurrentScrollParentId;
   bool                           mBuildCaret;
   bool                           mIgnoreSuppression;
   bool                           mHadToIgnoreSuppression;
@@ -2834,6 +2859,8 @@ public:
   virtual nsRegion GetOpaqueRegion(nsDisplayListBuilder* aBuilder, bool* aSnap) MOZ_OVERRIDE;
 
   NS_DISPLAY_DECL_NAME("SubDocument", TYPE_SUBDOCUMENT)
+protected:
+  ViewID mScrollParentId;
 };
 
 /**
@@ -2971,6 +2998,7 @@ public:
 protected:
   nsIFrame* mScrollFrame;
   nsIFrame* mScrolledFrame;
+  ViewID mScrollParentId;
 };
 
 /**

layout/generic/nsGfxScrollFrame.cpp

@@ -2523,8 +2523,41 @@ ScrollFrameHelper::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
     dirtyRect = ExpandRect(dirtyRect);
   }
 
+  // Since making new layers is expensive, only use nsDisplayScrollLayer
+  // if the area is scrollable and we're the content process (unless we're on
+  // B2G, where we support async scrolling for scrollable elements in the
+  // parent process as well).
+  // When a displayport is being used, force building of a layer so that
+  // CompositorParent can always find the scrollable layer for the root content
+  // document.
+  // If the element is marked 'scrollgrab', also force building of a layer
+  // so that APZ can implement scroll grabbing.
+  mShouldBuildScrollableLayer = usingDisplayport || nsContentUtils::HasScrollgrab(mOuter->GetContent());
+  bool shouldBuildLayer = false;
+  if (mShouldBuildScrollableLayer) {
+    shouldBuildLayer = true;
+  } else {
+    shouldBuildLayer =
+      nsLayoutUtils::WantSubAPZC() &&
+      WantAsyncScroll() &&
+      // If we are the root scroll frame for the display root then we don't need a scroll
+      // info layer to make a RecordFrameMetrics call for us as
+      // nsDisplayList::PaintForFrame already calls RecordFrameMetrics for us.
+      (!mIsRoot || aBuilder->RootReferenceFrame()->PresContext() != mOuter->PresContext());
+  }
+
   nsDisplayListCollection scrolledContent;
   {
+    // Note that setting the current scroll parent id here means that positioned children
+    // of this scroll info layer will pick up the scroll info layer as their scroll handoff
+    // parent. This is intentional because that is what happens for positioned children
+    // of scroll layers, and we want to maintain consistent behaviour between scroll layers
+    // and scroll info layers.
+    nsDisplayListBuilder::AutoCurrentScrollParentIdSetter idSetter(
+        aBuilder,
+        shouldBuildLayer && mScrolledFrame->GetContent()
+            ? nsLayoutUtils::FindOrCreateIDFor(mScrolledFrame->GetContent())
+            : aBuilder->GetCurrentScrollParentId());
     DisplayListClipState::AutoSaveRestore clipState(aBuilder);
 
     if (usingDisplayport) {
@@ -2585,29 +2618,6 @@ ScrollFrameHelper::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
     }
   }
 
-  // Since making new layers is expensive, only use nsDisplayScrollLayer
-  // if the area is scrollable and we're the content process (unless we're on
-  // B2G, where we support async scrolling for scrollable elements in the
-  // parent process as well).
-  // When a displayport is being used, force building of a layer so that
-  // CompositorParent can always find the scrollable layer for the root content
-  // document.
-  // If the element is marked 'scrollgrab', also force building of a layer
-  // so that APZ can implement scroll grabbing.
-  mShouldBuildScrollableLayer = usingDisplayport || nsContentUtils::HasScrollgrab(mOuter->GetContent());
-  bool shouldBuildLayer = false;
-  if (mShouldBuildScrollableLayer) {
-    shouldBuildLayer = true;
-  } else {
-    shouldBuildLayer =
-      nsLayoutUtils::WantSubAPZC() &&
-      WantAsyncScroll() &&
-      // If we are the root scroll frame for the display root then we don't need a scroll
-      // info layer to make a RecordFrameMetrics call for us as
-      // nsDisplayList::PaintForFrame already calls RecordFrameMetrics for us.
-      (!mIsRoot || aBuilder->RootReferenceFrame()->PresContext() != mOuter->PresContext());
-  }
-
   if (shouldBuildLayer) {
     // ScrollLayerWrapper must always be created because it initializes the
     // scroll layer count. The display lists depend on this.

layout/generic/nsSubDocumentFrame.cpp

@@ -436,6 +436,12 @@ nsSubDocumentFrame::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
     }
 
     if (subdocRootFrame) {
+      nsDisplayListBuilder::AutoCurrentScrollParentIdSetter idSetter(
+          aBuilder,
+          ignoreViewportScrolling && subdocRootFrame->GetContent()
+              ? nsLayoutUtils::FindOrCreateIDFor(subdocRootFrame->GetContent())
+              : aBuilder->GetCurrentScrollParentId());
+
       aBuilder->SetAncestorHasTouchEventHandler(false);
       subdocRootFrame->
         BuildDisplayListForStackingContext(aBuilder, dirty, &childItems);