WIP: basic scroll-anchoring attempt.scroll-anchoring-wip

This is incomplete and won't build due to prerequisites.

1 files changed, 30 insertions, 0 deletions

diff --git a/layout/generic/nsGfxScrollFrame.h b/layout/generic/nsGfxScrollFrame.h
index 41957d5e55..49e22b9224 100644
--- a/layout/generic/nsGfxScrollFrame.h
+++ b/layout/generic/nsGfxScrollFrame.h
@@ -458,6 +458,11 @@ public:
     return mSuppressScrollbarRepaints;
   }
 
+
+  void ScrollAnchorWillDestroy();
+
+  void ApplyScrollAnchorOffsetAdjustment();
+
   // owning references to the nsIAnonymousContentCreator-built content
   nsCOMPtr<nsIContent> mHScrollbarContent;
   nsCOMPtr<nsIContent> mVScrollbarContent;
@@ -472,6 +477,7 @@ public:
   nsIFrame* mScrolledFrame;
   nsIFrame* mScrollCornerBox;
   nsIFrame* mResizerBox;
+  nsIFrame* mAnchorNode;
   nsContainerFrame* mOuter;
   RefPtr<AsyncScroll> mAsyncScroll;
   RefPtr<AsyncSmoothMSDScroll> mAsyncSmoothMSDScroll;
@@ -500,6 +506,11 @@ public:
   // other than trying to restore mRestorePos.
   nsPoint mLastPos;
 
+  // The last scroll position of the scroll anchor node. This is in the same
+  // coordinate space as mScrollPort, that is, relative to the parent of this
+  // scrollable frame.
+  nsPoint mLastAnchorPos;
+
   nsExpirationState mActivityExpirationState;
 
   nsCOMPtr<nsITimer> mScrollActivityTimer;
@@ -619,6 +630,9 @@ protected:
     bool mOldSuppressValue;
   };
 
+  void UpdateScrollAnchor();
+  nsIFrame* SelectScrollAnchorImpl(nsIFrame* aNode);
+
   /**
    * @note This method might destroy the frame, pres shell and other objects.
    */
@@ -1047,6 +1061,14 @@ public:
   virtual mozilla::a11y::AccType AccessibleType() override;
 #endif
 
+  virtual void ScrollAnchorWillDestroy() override {
+    mHelper.ScrollAnchorWillDestroy();
+  }
+
+  virtual void ApplyScrollAnchorOffsetAdjustment() override {
+    mHelper.ApplyScrollAnchorOffsetAdjustment();
+  }
+
 protected:
   nsHTMLScrollFrame(nsStyleContext* aContext, bool aIsRoot);
   void SetSuppressScrollbarUpdate(bool aSuppress) {
@@ -1471,6 +1493,14 @@ public:
   virtual nsresult GetFrameName(nsAString& aResult) const override;
 #endif
 
+  virtual void ScrollAnchorWillDestroy() override {
+    mHelper.ScrollAnchorWillDestroy();
+  }
+
+  virtual void ApplyScrollAnchorOffsetAdjustment() override {
+    mHelper.ApplyScrollAnchorOffsetAdjustment();
+  }
+
 protected:
   nsXULScrollFrame(nsStyleContext* aContext, bool aIsRoot,
                    bool aClipAllDescendants);