Bug 1259296 - Do not scroll snap on the main thread for wheel events handled by APZ. r=kats

MozReview-Commit-ID: DudrJuO4pFM

--HG--
extra : source : a9468a25f1b937c49c5f801069d2cdc2cd610bdd
extra : histedit_source : 18d04bcb32288c7713a162f0ee33650f6f10926f

dom/events/EventStateManager.cpp

@@ -3176,19 +3176,6 @@ EventStateManager::PostHandleEvent(nsPresContext* aPresContext,
       if (pluginFrame) {
         MOZ_ASSERT(pluginFrame->WantsToHandleWheelEventAsDefaultAction());
         action = WheelPrefs::ACTION_SEND_TO_PLUGIN;
-      } else if (!wheelEvent->mMayHaveMomentum &&
-            nsLayoutUtils::IsScrollFrameWithSnapping(frameToScroll)) {
-        // If the target has scroll-snapping points then we want to handle
-        // the wheel event on the main thread even if we have APZ enabled. Do
-        // so and let the APZ know that it should ignore this event. However,
-        // if the wheel event is synthesized from a Mac trackpad or other device
-        // that can generate additional momentum events, then we should allow
-        // APZ to handle it, because it will track the velocity and predicted
-        // destination from the momentum.
-        if (wheelEvent->mFlags.mHandledByAPZ) {
-          wheelEvent->PreventDefault();
-        }
-        action = WheelPrefs::GetInstance()->ComputeActionFor(wheelEvent);
       } else if (wheelEvent->mFlags.mHandledByAPZ) {
         action = WheelPrefs::ACTION_NONE;
       } else {

layout/base/nsDisplayList.cpp

@@ -3530,12 +3530,6 @@ nsDisplayLayerEventRegions::AddFrame(nsDisplayListBuilder* aBuilder,
     if (pluginFrame && pluginFrame->WantsToHandleWheelEventAsDefaultAction()) {
       mDispatchToContentHitRegion.Or(mDispatchToContentHitRegion, borderBox);
     }
-  } else if (gfxPlatform::GetPlatform()->SupportsApzWheelInput() &&
-             nsLayoutUtils::IsScrollFrameWithSnapping(aFrame->GetParent())) {
-    // If the frame is the inner content of a scrollable frame with snap-points
-    // then we want to handle wheel events for it on the main thread. Add it to
-    // the d-t-c region so that APZ waits for the main thread.
-    mDispatchToContentHitRegion.Or(mDispatchToContentHitRegion, borderBox);
   }
 
   // Touch action region

layout/base/nsLayoutUtils.cpp

@@ -8968,16 +8968,6 @@ nsLayoutUtils::GetSelectionBoundingRect(Selection* aSel)
   return res;
 }
 
-/* static */ bool
-nsLayoutUtils::IsScrollFrameWithSnapping(nsIFrame* aFrame)
-{
-  nsIScrollableFrame* sf = do_QueryFrame(aFrame);
-  if (!sf) {
-    return false;
-  }
-  return sf->IsScrollFrameWithSnapping();
-}
-
 /* static */ nsBlockFrame*
 nsLayoutUtils::GetFloatContainingBlock(nsIFrame* aFrame)
 {

layout/base/nsLayoutUtils.h

@@ -2792,10 +2792,6 @@ public:
    */
   static nsRect GetSelectionBoundingRect(mozilla::dom::Selection* aSel);
 
-  /**
-   * Returns true if the given frame is a scrollframe and it has snap points.
-   */
-  static bool IsScrollFrameWithSnapping(nsIFrame* aFrame);
   /**
    * Calculate the bounding rect of |aContent|, relative to the origin
    * of the scrolled content of |aRootScrollFrame|.

layout/forms/nsListControlFrame.h

@@ -108,9 +108,6 @@ public:
   virtual nsresult SetFormProperty(nsIAtom* aName, const nsAString& aValue) override;
   virtual void SetFocus(bool aOn = true, bool aRepaint = false) override;
 
-  virtual bool IsScrollFrameWithSnapping() const override {
-    return false;
-  }
   virtual mozilla::ScrollbarStyles GetScrollbarStyles() const override;
   virtual bool ShouldPropagateComputedBSizeToScrolledContent() const override;
 

layout/generic/nsGfxScrollFrame.cpp

@@ -3632,26 +3632,6 @@ static void HandleScrollPref(nsIScrollable *aScrollable, int32_t aOrientation,
   }
 }
 
-bool
-ScrollFrameHelper::IsScrollFrameWithSnapping() const
-{
-  nsPresContext* presContext = mOuter->PresContext();
-  if (!presContext->IsDynamic() &&
-      !(mIsRoot && presContext->HasPaginatedScrolling())) {
-    return false;
-  }
-
-  if (!mIsRoot) {
-    const nsStyleDisplay& display = *mOuter->StyleDisplay();
-    return display.mScrollSnapTypeY != NS_STYLE_SCROLL_SNAP_TYPE_NONE ||
-           display.mScrollSnapTypeX != NS_STYLE_SCROLL_SNAP_TYPE_NONE;
-  } else {
-    const ScrollbarStyles& display = presContext->GetViewportScrollbarStylesOverride();
-    return display.mScrollSnapTypeY != NS_STYLE_SCROLL_SNAP_TYPE_NONE ||
-           display.mScrollSnapTypeX != NS_STYLE_SCROLL_SNAP_TYPE_NONE;
-  }
-}
-
 ScrollbarStyles
 ScrollFrameHelper::GetScrollbarStylesFromFrame() const
 {

layout/generic/nsGfxScrollFrame.h

@@ -58,7 +58,6 @@ public:
   ScrollFrameHelper(nsContainerFrame* aOuter, bool aIsRoot);
   ~ScrollFrameHelper();
 
-  bool IsScrollFrameWithSnapping() const;
   mozilla::ScrollbarStyles GetScrollbarStylesFromFrame() const;
 
   // If a child frame was added or removed on the scrollframe,
@@ -752,9 +751,6 @@ public:
   virtual nsIFrame* GetScrolledFrame() const override {
     return mHelper.GetScrolledFrame();
   }
-  virtual bool IsScrollFrameWithSnapping() const override {
-    return mHelper.IsScrollFrameWithSnapping();
-  }
   virtual mozilla::ScrollbarStyles GetScrollbarStyles() const override {
     return mHelper.GetScrollbarStylesFromFrame();
   }
@@ -1168,9 +1164,6 @@ public:
   virtual nsIFrame* GetScrolledFrame() const override {
     return mHelper.GetScrolledFrame();
   }
-  virtual bool IsScrollFrameWithSnapping() const override {
-    return mHelper.IsScrollFrameWithSnapping();
-  }
   virtual mozilla::ScrollbarStyles GetScrollbarStyles() const override {
     return mHelper.GetScrollbarStylesFromFrame();
   }

layout/generic/nsIScrollableFrame.h

@@ -65,8 +65,6 @@ public:
    */
   virtual mozilla::ScrollbarStyles GetScrollbarStyles() const = 0;
 
-  virtual bool IsScrollFrameWithSnapping() const = 0;
-
   enum { HORIZONTAL = 0x01, VERTICAL = 0x02 };
   /**
    * Return the scrollbars which are visible. It's OK to call this during reflow