Make scroll translation transform nodes reference scroll nodes

third_party/WebKit/Source/platform/graphics/paint/ScrollPaintPropertyNode.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef ScrollPaintPropertyNode_h
 #define ScrollPaintPropertyNode_h
 
 #include "platform/PlatformExport.h"
 #include "platform/geometry/FloatSize.h"
-#include "platform/graphics/CompositorElementId.h"
-#include "platform/graphics/paint/TransformPaintPropertyNode.h"
 #include "platform/scroll/MainThreadScrollingReason.h"
 #include "wtf/PassRefPtr.h"
 #include "wtf/RefCounted.h"
 #include "wtf/RefPtr.h"
 #include "wtf/text/WTFString.h"
 
 #include <iosfwd>
 
 namespace blink {
 
 using MainThreadScrollingReasons = uint32_t;
 
-// A scroll node contains auxiliary scrolling information for threaded scrolling
-// which includes how far an area can be scrolled, which transform node contains
-// the scroll offset, etc.
+// A scroll node contains auxiliary scrolling information which includes how far
+// an area can be scrolled, main thread scrolling reasons, etc. Scroll nodes
+// are owned by TransformPaintPropertyNodes that are used for the scroll offset
+// translation.

[pdr., 2017/01/25 19:51:09]

Walter pointed out that we should put a comment here noting that the scroll
paint property tree differs from the other trees since it is (or will be)
embedded in the transform tree. We could even consider naming this
RareScrollNode or something like that.

 //
 // Main thread scrolling reasons force scroll updates to go to the main thread
 // and can have dependencies on other nodes. For example, all parents of a
 // scroll node with background attachment fixed set should also have it set.
 class PLATFORM_EXPORT ScrollPaintPropertyNode
     : public RefCounted<ScrollPaintPropertyNode> {
  public:
   // This node is really a sentinel, and does not represent a real scroll.
   static ScrollPaintPropertyNode* root();
 
   static PassRefPtr<ScrollPaintPropertyNode> create(
       PassRefPtr<const ScrollPaintPropertyNode> parent,
-      PassRefPtr<const TransformPaintPropertyNode> scrollOffsetTranslation,
       const IntSize& clip,
       const IntSize& bounds,
       bool userScrollableHorizontal,
       bool userScrollableVertical,
-      MainThreadScrollingReasons mainThreadScrollingReasons,
-      const CompositorElementId& compositorElementId = CompositorElementId()) {
+      MainThreadScrollingReasons mainThreadScrollingReasons) {
     return adoptRef(new ScrollPaintPropertyNode(
-        std::move(parent), std::move(scrollOffsetTranslation), clip, bounds,
-        userScrollableHorizontal, userScrollableVertical,
-        mainThreadScrollingReasons, compositorElementId));
+        std::move(parent), clip, bounds, userScrollableHorizontal,
+        userScrollableVertical, mainThreadScrollingReasons));
   }
 
-  void update(
-      PassRefPtr<const ScrollPaintPropertyNode> parent,
-      PassRefPtr<const TransformPaintPropertyNode> scrollOffsetTranslation,
-      const IntSize& clip,
-      const IntSize& bounds,
-      bool userScrollableHorizontal,
-      bool userScrollableVertical,
-      MainThreadScrollingReasons mainThreadScrollingReasons,
-      CompositorElementId compositorElementId = CompositorElementId()) {
+  void update(PassRefPtr<const ScrollPaintPropertyNode> parent,
+              const IntSize& clip,
+              const IntSize& bounds,
+              bool userScrollableHorizontal,
+              bool userScrollableVertical,
+              MainThreadScrollingReasons mainThreadScrollingReasons) {
     DCHECK(!isRoot());
     DCHECK(parent != this);
     m_parent = parent;
-    DCHECK(scrollOffsetTranslation->matrix().isIdentityOr2DTranslation());
-    m_scrollOffsetTranslation = scrollOffsetTranslation;
     m_clip = clip;
     m_bounds = bounds;
     m_userScrollableHorizontal = userScrollableHorizontal;
     m_userScrollableVertical = userScrollableVertical;
     m_mainThreadScrollingReasons = mainThreadScrollingReasons;
-    m_compositorElementId = compositorElementId;
   }
 
   const ScrollPaintPropertyNode* parent() const { return m_parent.get(); }
   bool isRoot() const { return !m_parent; }
 
-  // Transform that the scroll is relative to.
-  const TransformPaintPropertyNode* scrollOffsetTranslation() const {
-    return m_scrollOffsetTranslation.get();
-  }
-
   // The clipped area that contains the scrolled content.
   const IntSize& clip() const { return m_clip; }
 
   // The bounds of the content that is scrolled within |clip|.
   const IntSize& bounds() const { return m_bounds; }
 
   bool userScrollableHorizontal() const { return m_userScrollableHorizontal; }
   bool userScrollableVertical() const { return m_userScrollableVertical; }
 
   // Return reason bitfield with values from cc::MainThreadScrollingReason.
   MainThreadScrollingReasons mainThreadScrollingReasons() const {
     return m_mainThreadScrollingReasons;
   }
 
-  const CompositorElementId& compositorElementId() const {
-    return m_compositorElementId;
-  }
-
   // Main thread scrolling reason for the threaded scrolling disabled setting.
   bool threadedScrollingDisabled() const {
     return m_mainThreadScrollingReasons &
            MainThreadScrollingReason::kThreadedScrollingDisabled;
   }
 
   // Main thread scrolling reason for background attachment fixed descendants.
   bool hasBackgroundAttachmentFixedDescendants() const {
     return m_mainThreadScrollingReasons &
            MainThreadScrollingReason::kHasBackgroundAttachmentFixedObjects;
   }
 
 #if DCHECK_IS_ON()
   // The clone function is used by FindPropertiesNeedingUpdate.h for recording
   // a scroll node before it has been updated, to later detect changes.
   PassRefPtr<ScrollPaintPropertyNode> clone() const {
     RefPtr<ScrollPaintPropertyNode> cloned =
         adoptRef(new ScrollPaintPropertyNode(
-            m_parent, m_scrollOffsetTranslation, m_clip, m_bounds,
-            m_userScrollableHorizontal, m_userScrollableVertical,
-            m_mainThreadScrollingReasons, m_compositorElementId));
+            m_parent, m_clip, m_bounds, m_userScrollableHorizontal,
+            m_userScrollableVertical, m_mainThreadScrollingReasons));
     return cloned;
   }
 
   // The equality operator is used by FindPropertiesNeedingUpdate.h for checking
   // if a scroll node has changed.
   bool operator==(const ScrollPaintPropertyNode& o) const {
-    return m_parent == o.m_parent &&
-           m_scrollOffsetTranslation == o.m_scrollOffsetTranslation &&
-           m_clip == o.m_clip && m_bounds == o.m_bounds &&
+    return m_parent == o.m_parent && m_clip == o.m_clip &&
+           m_bounds == o.m_bounds &&
            m_userScrollableHorizontal == o.m_userScrollableHorizontal &&
            m_userScrollableVertical == o.m_userScrollableVertical &&
-           m_mainThreadScrollingReasons == o.m_mainThreadScrollingReasons &&
-           m_compositorElementId == o.m_compositorElementId;
+           m_mainThreadScrollingReasons == o.m_mainThreadScrollingReasons;
   }
 
   String toTreeString() const;
 #endif
 
   String toString() const;
 
  private:
-  ScrollPaintPropertyNode(
-      PassRefPtr<const ScrollPaintPropertyNode> parent,
-      PassRefPtr<const TransformPaintPropertyNode> scrollOffsetTranslation,
-      IntSize clip,
-      IntSize bounds,
-      bool userScrollableHorizontal,
-      bool userScrollableVertical,
-      MainThreadScrollingReasons mainThreadScrollingReasons,
-      CompositorElementId compositorElementId)
+  ScrollPaintPropertyNode(PassRefPtr<const ScrollPaintPropertyNode> parent,
+                          IntSize clip,
+                          IntSize bounds,
+                          bool userScrollableHorizontal,
+                          bool userScrollableVertical,
+                          MainThreadScrollingReasons mainThreadScrollingReasons)
       : m_parent(parent),
-        m_scrollOffsetTranslation(scrollOffsetTranslation),
         m_clip(clip),
         m_bounds(bounds),
         m_userScrollableHorizontal(userScrollableHorizontal),
         m_userScrollableVertical(userScrollableVertical),
-        m_mainThreadScrollingReasons(mainThreadScrollingReasons),
-        m_compositorElementId(compositorElementId) {
-    DCHECK(m_scrollOffsetTranslation->matrix().isIdentityOr2DTranslation());
-  }
+        m_mainThreadScrollingReasons(mainThreadScrollingReasons) {}
 
   RefPtr<const ScrollPaintPropertyNode> m_parent;
-  RefPtr<const TransformPaintPropertyNode> m_scrollOffsetTranslation;
   IntSize m_clip;
   IntSize m_bounds;
   bool m_userScrollableHorizontal : 1;
   bool m_userScrollableVertical : 1;
   MainThreadScrollingReasons m_mainThreadScrollingReasons;
-  CompositorElementId m_compositorElementId;
 };
 
 // Redeclared here to avoid ODR issues.
 // See platform/testing/PaintPrinters.h.
 void PrintTo(const ScrollPaintPropertyNode&, std::ostream*);
 
 }  // namespace blink
 
 #endif  // ScrollPaintPropertyNode_h