1 files changed, 110 insertions, 0 deletions
diff --git a/layout/generic/StickyScrollContainer.h b/layout/generic/StickyScrollContainer.h
new file mode 100644
index 0000000000..1d26982a92
--- /dev/null
+++ b/layout/generic/StickyScrollContainer.h
@@ -0,0 +1,110 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=2 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * compute sticky positioning, both during reflow and when the scrolling
+ * container scrolls
+ */
+
+#ifndef StickyScrollContainer_h
+#define StickyScrollContainer_h
+
+#include "nsPoint.h"
+#include "nsTArray.h"
+#include "nsIScrollPositionListener.h"
+
+struct nsRect;
+class nsIFrame;
+class nsIScrollableFrame;
+
+namespace mozilla {
+
+class StickyScrollContainer final : public nsIScrollPositionListener
+{
+public:
+  /**
+   * Find (and create if necessary) the StickyScrollContainer associated with
+   * the scroll container of the given frame, if a scroll container exists.
+   */
+  static StickyScrollContainer* GetStickyScrollContainerForFrame(nsIFrame* aFrame);
+
+  /**
+   * Find the StickyScrollContainer associated with the given scroll frame,
+   * if it exists.
+   */
+  static StickyScrollContainer* GetStickyScrollContainerForScrollFrame(nsIFrame* aScrollFrame);
+
+  /**
+   * aFrame may have moved into or out of a scroll frame's frame subtree.
+   */
+  static void NotifyReparentedFrameAcrossScrollFrameBoundary(nsIFrame* aFrame,
+                                                             nsIFrame* aOldParent);
+
+  void AddFrame(nsIFrame* aFrame) {
+    mFrames.AppendElement(aFrame);
+  }
+  void RemoveFrame(nsIFrame* aFrame) {
+    mFrames.RemoveElement(aFrame);
+  }
+
+  nsIScrollableFrame* ScrollFrame() const {
+    return mScrollFrame;
+  }
+
+  // Compute the offsets for a sticky position element
+  static void ComputeStickyOffsets(nsIFrame* aFrame);
+
+  /**
+   * Compute the position of a sticky positioned frame, based on information
+   * stored in its properties along with our scroll frame and scroll position.
+   */
+  nsPoint ComputePosition(nsIFrame* aFrame) const;
+
+  /**
+   * Compute where a frame should not scroll with the page, represented by the
+   * difference of two rectangles.
+   */
+  void GetScrollRanges(nsIFrame* aFrame, nsRect* aOuter, nsRect* aInner) const;
+
+  /**
+   * Compute and set the position of a frame and its following continuations.
+   */
+  void PositionContinuations(nsIFrame* aFrame);
+
+  /**
+   * Compute and set the position of all sticky frames, given the current
+   * scroll position of the scroll frame. If not in reflow, aSubtreeRoot should
+   * be null; otherwise, overflow-area updates will be limited to not affect
+   * aSubtreeRoot or its ancestors.
+   */
+  void UpdatePositions(nsPoint aScrollPosition, nsIFrame* aSubtreeRoot);
+
+  // nsIScrollPositionListener
+  virtual void ScrollPositionWillChange(nscoord aX, nscoord aY) override;
+  virtual void ScrollPositionDidChange(nscoord aX, nscoord aY) override;
+
+  ~StickyScrollContainer();
+
+private:
+  explicit StickyScrollContainer(nsIScrollableFrame* aScrollFrame);
+
+  /**
+   * Compute two rectangles that determine sticky positioning: |aStick|, based
+   * on the scroll container, and |aContain|, based on the containing block.
+   * Sticky positioning keeps the frame position (its upper-left corner) always
+   * within |aContain| and secondarily within |aStick|.
+   */
+  void ComputeStickyLimits(nsIFrame* aFrame, nsRect* aStick,
+                           nsRect* aContain) const;
+
+  nsIScrollableFrame* const mScrollFrame;
+  nsTArray<nsIFrame*> mFrames;
+  nsPoint mScrollPosition;
+};
+
+} // namespace mozilla
+
+#endif /* StickyScrollContainer_h */