Bug 1305957 part 4 - Add basic ScrollAnchorContainer implementation. r=hiro

This commit adds a barebones class called 'ScrollAnchorContainer' that will
contain most of the logic for scroll anchoring. It is owned as a member of
ScrollFrameHelper, and has the same lifetime.

Differential Revision: https://phabricator.services.mozilla.com/D13267

--HG--
extra : rebase_source : 41f6f7691af60401f18f98a89f1878cfad2e74d3
extra : source : 3033401ef320414ef5f489c53526d015c38a89d7

layout/generic/ScrollAnchorContainer.cpp

@@ -0,0 +1,44 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 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/. */
+
+#include "ScrollAnchorContainer.h"
+
+#include "nsGfxScrollFrame.h"
+#include "nsLayoutUtils.h"
+
+#define ANCHOR_LOG(...)
+// #define ANCHOR_LOG(...) printf_stderr("ANCHOR: " __VA_ARGS__)
+
+namespace mozilla {
+namespace layout {
+
+ScrollAnchorContainer::ScrollAnchorContainer(ScrollFrameHelper* aScrollFrame)
+    : mScrollFrame(aScrollFrame) {}
+
+ScrollAnchorContainer::~ScrollAnchorContainer() {}
+
+ScrollAnchorContainer* ScrollAnchorContainer::FindFor(nsIFrame* aFrame) {
+  aFrame = aFrame->GetParent();
+  if (!aFrame) {
+    return nullptr;
+  }
+  nsIScrollableFrame* nearest = nsLayoutUtils::GetNearestScrollableFrame(
+      aFrame, nsLayoutUtils::SCROLLABLE_SAME_DOC |
+                  nsLayoutUtils::SCROLLABLE_INCLUDE_HIDDEN);
+  if (nearest) {
+    return nearest->GetAnchor();
+  }
+  return nullptr;
+}
+
+nsIFrame* ScrollAnchorContainer::Frame() const { return mScrollFrame->mOuter; }
+
+nsIScrollableFrame* ScrollAnchorContainer::ScrollableFrame() const {
+  return Frame()->GetScrollTargetFrame();
+}
+
+}  // namespace layout
+}  // namespace mozilla

layout/generic/ScrollAnchorContainer.h

@@ -0,0 +1,55 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 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/. */
+
+#ifndef mozilla_layout_ScrollAnchorContainer_h_
+#define mozilla_layout_ScrollAnchorContainer_h_
+
+namespace mozilla {
+class ScrollFrameHelper;
+}  // namespace mozilla
+
+namespace mozilla {
+namespace layout {
+
+/**
+ * A scroll anchor container finds a descendent element of a scrollable frame
+ * to be an anchor node. After every reflow, the scroll anchor will apply
+ * scroll adjustments to keep the anchor node in the same relative position.
+ *
+ * See: https://drafts.csswg.org/css-scroll-anchoring/
+ */
+class ScrollAnchorContainer final {
+ public:
+  explicit ScrollAnchorContainer(ScrollFrameHelper* aScrollFrame);
+  ~ScrollAnchorContainer();
+
+  /**
+   * Returns the nearest scroll anchor container that could select aFrame as an
+   * anchor node.
+   */
+  static ScrollAnchorContainer* FindFor(nsIFrame* aFrame);
+
+  /**
+   * Returns the frame that owns this scroll anchor container. This is always
+   * non-null.
+   */
+  nsIFrame* Frame() const;
+
+  /**
+   * Returns the frame that owns this scroll anchor container as a scrollable
+   * frame. This is always non-null.
+   */
+  nsIScrollableFrame* ScrollableFrame() const;
+
+ private:
+  // The owner of this scroll anchor container
+  ScrollFrameHelper* mScrollFrame;
+};
+
+}  // namespace layout
+}  // namespace mozilla
+
+#endif  // mozilla_layout_ScrollAnchorContainer_h_

layout/generic/moz.build

@@ -145,6 +145,7 @@ EXPORTS.mozilla += [
 
 EXPORTS.mozilla.layout += [
     'FrameChildList.h',
+    'ScrollAnchorContainer.h',
 ]
 
 UNIFIED_SOURCES += [
@@ -202,6 +203,7 @@ UNIFIED_SOURCES += [
     'ReflowInput.cpp',
     'ReflowOutput.cpp',
     'RubyUtils.cpp',
+    'ScrollAnchorContainer.cpp',
     'ScrollAnimationBezierPhysics.cpp',
     'ScrollAnimationMSDPhysics.cpp',
     'ScrollbarActivity.cpp',

layout/generic/nsGfxScrollFrame.cpp

@@ -1960,6 +1960,7 @@ ScrollFrameHelper::ScrollFrameHelper(nsContainerFrame* aOuter, bool aIsRoot)
       mLastUpdateFramesPos(-1, -1),
       mDisplayPortAtLastFrameUpdate(),
       mScrollParentID(mozilla::layers::ScrollableLayerGuid::NULL_SCROLL_ID),
+      mAnchor(this),
       mAllowScrollOriginDowngrade(false),
       mHadDisplayPortAtLastFrameUpdate(false),
       mNeverHasVerticalScrollbar(false),

layout/generic/nsGfxScrollFrame.h

@@ -25,6 +25,7 @@
 #include "TextOverflow.h"
 #include "ScrollVelocityQueue.h"
 #include "mozilla/PresState.h"
+#include "mozilla/layout/ScrollAnchorContainer.h"
 
 class nsPresContext;
 class nsIPresShell;
@@ -52,6 +53,7 @@ class ScrollFrameHelper : public nsIReflowCallback {
   typedef mozilla::layers::ScrollSnapInfo ScrollSnapInfo;
   typedef mozilla::layers::Layer Layer;
   typedef mozilla::layers::LayerManager LayerManager;
+  typedef mozilla::layout::ScrollAnchorContainer ScrollAnchorContainer;
 
   class AsyncScroll;
   class AsyncSmoothMSDScroll;
@@ -566,6 +568,8 @@ class ScrollFrameHelper : public nsIReflowCallback {
   // Timer to remove the displayport some time after scrolling has stopped
   nsCOMPtr<nsITimer> mDisplayPortExpiryTimer;
 
+  ScrollAnchorContainer mAnchor;
+
   bool mAllowScrollOriginDowngrade : 1;
   bool mHadDisplayPortAtLastFrameUpdate : 1;
   bool mNeverHasVerticalScrollbar : 1;
@@ -723,6 +727,7 @@ class nsHTMLScrollFrame : public nsContainerFrame,
   typedef mozilla::ScrollFrameHelper ScrollFrameHelper;
   typedef mozilla::CSSIntPoint CSSIntPoint;
   typedef mozilla::ScrollReflowInput ScrollReflowInput;
+  typedef mozilla::layout::ScrollAnchorContainer ScrollAnchorContainer;
   friend nsHTMLScrollFrame* NS_NewHTMLScrollFrame(nsIPresShell* aPresShell,
                                                   ComputedStyle* aStyle,
                                                   bool aIsRoot);
@@ -1112,6 +1117,14 @@ class nsHTMLScrollFrame : public nsContainerFrame,
     return mHelper.IsRootScrollFrameOfDocument();
   }
 
+  virtual const ScrollAnchorContainer* GetAnchor() const override {
+    return &mHelper.mAnchor;
+  }
+
+  virtual ScrollAnchorContainer* GetAnchor() override {
+    return &mHelper.mAnchor;
+  }
+
   // Return the scrolled frame.
   void AppendDirectlyOwnedAnonBoxes(nsTArray<OwnedAnonBox>& aResult) override {
     aResult.AppendElement(OwnedAnonBox(mHelper.GetScrolledFrame()));
@@ -1174,6 +1187,7 @@ class nsXULScrollFrame final : public nsBoxFrame,
  public:
   typedef mozilla::ScrollFrameHelper ScrollFrameHelper;
   typedef mozilla::CSSIntPoint CSSIntPoint;
+  typedef mozilla::layout::ScrollAnchorContainer ScrollAnchorContainer;
 
   NS_DECL_QUERYFRAME
   NS_DECL_FRAMEARENA_HELPERS(nsXULScrollFrame)
@@ -1577,6 +1591,14 @@ class nsXULScrollFrame final : public nsBoxFrame,
     return mHelper.IsRootScrollFrameOfDocument();
   }
 
+  virtual const ScrollAnchorContainer* GetAnchor() const override {
+    return &mHelper.mAnchor;
+  }
+
+  virtual ScrollAnchorContainer* GetAnchor() override {
+    return &mHelper.mAnchor;
+  }
+
   // Return the scrolled frame.
   void AppendDirectlyOwnedAnonBoxes(nsTArray<OwnedAnonBox>& aResult) override {
     aResult.AppendElement(OwnedAnonBox(mHelper.GetScrolledFrame()));

layout/generic/nsIScrollableFrame.h

@@ -39,6 +39,9 @@ struct ScrollMetadata;
 class Layer;
 class LayerManager;
 }  // namespace layers
+namespace layout {
+class ScrollAnchorContainer;
+}  // namespace layout
 }  // namespace mozilla
 
 /**
@@ -51,6 +54,7 @@ class nsIScrollableFrame : public nsIScrollbarMediator {
   typedef mozilla::CSSIntPoint CSSIntPoint;
   typedef mozilla::ContainerLayerParameters ContainerLayerParameters;
   typedef mozilla::layers::ScrollSnapInfo ScrollSnapInfo;
+  typedef mozilla::layout::ScrollAnchorContainer ScrollAnchorContainer;
 
   NS_DECL_QUERYFRAME_TARGET(nsIScrollableFrame)
 
@@ -548,6 +552,12 @@ class nsIScrollableFrame : public nsIScrollbarMediator {
    * all (ie XUL documents) even though they may contain other scroll frames.
    */
   virtual bool IsRootScrollFrameOfDocument() const = 0;
+
+  /**
+   * Returns the scroll anchor associated with this scrollable frame.
+   */
+  virtual const ScrollAnchorContainer* GetAnchor() const = 0;
+  virtual ScrollAnchorContainer* GetAnchor() = 0;
 };
 
 #endif