Incrementally build main thread scrolling reasons [spv2]

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/paint/TransformPaintPropertyNode.h"
@@ skipping 14 matching lines @@
 //
 // 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:
   static ScrollPaintPropertyNode* root();
 
   static PassRefPtr<ScrollPaintPropertyNode> create(
-      PassRefPtr<ScrollPaintPropertyNode> parent,
+      PassRefPtr<const ScrollPaintPropertyNode> parent,
       PassRefPtr<const TransformPaintPropertyNode> scrollOffsetTranslation,
       const IntSize& clip,
       const IntSize& bounds,
       bool userScrollableHorizontal,
-      bool userScrollableVertical) {
+      bool userScrollableVertical,
+      bool threadedScrollingDisabled,
+      bool hasBackgroundAttachmentFixedDescendants) {
     return adoptRef(new ScrollPaintPropertyNode(
         std::move(parent), std::move(scrollOffsetTranslation), clip, bounds,
-        userScrollableHorizontal, userScrollableVertical));
+        userScrollableHorizontal, userScrollableVertical,
+        threadedScrollingDisabled, hasBackgroundAttachmentFixedDescendants));
   }
 
   void update(
-      PassRefPtr<ScrollPaintPropertyNode> parent,
+      PassRefPtr<const ScrollPaintPropertyNode> parent,
       PassRefPtr<const TransformPaintPropertyNode> scrollOffsetTranslation,
       const IntSize& clip,
       const IntSize& bounds,
       bool userScrollableHorizontal,
-      bool userScrollableVertical) {
+      bool userScrollableVertical,
+      bool threadedScrollingDisabled,
+      bool hasBackgroundAttachmentFixedDescendants) {
     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 = 0;
+    m_threadedScrollingDisabled = threadedScrollingDisabled;
+    m_hasBackgroundAttachmentFixedDescendants =
+        hasBackgroundAttachmentFixedDescendants;
   }
 
-  ScrollPaintPropertyNode* parent() const { return m_parent.get(); }
+  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;
+    MainThreadScrollingReasons reasons = 0;
+    if (threadedScrollingDisabled())
+      reasons |= MainThreadScrollingReason::kThreadedScrollingDisabled;
+    if (hasBackgroundAttachmentFixedDescendants()) {
+      reasons |=
+          MainThreadScrollingReason::kHasBackgroundAttachmentFixedObjects;
+    }
+    return reasons;
   }
-  bool hasMainThreadScrollingReasons(MainThreadScrollingReasons reasons) const {
-    return m_mainThreadScrollingReasons & reasons;
+
+  // Main thread scrolling reason for the threaded scrolling disabled setting.
+  bool threadedScrollingDisabled() const { return m_threadedScrollingDisabled; }
+
+  // Main thread scrolling reason for background attachment fixed descendants.
+  bool hasBackgroundAttachmentFixedDescendants() const {
+    return m_hasBackgroundAttachmentFixedDescendants;
   }
-  void addMainThreadScrollingReasons(MainThreadScrollingReasons reasons) {
-    m_mainThreadScrollingReasons |= reasons;
-  }
-  void clearMainThreadScrollingReasons() { m_mainThreadScrollingReasons = 0; }
 
 #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));
-    cloned->addMainThreadScrollingReasons(m_mainThreadScrollingReasons);
+            m_userScrollableHorizontal, m_userScrollableVertical,
+            m_threadedScrollingDisabled,
+            m_hasBackgroundAttachmentFixedDescendants));
     return cloned;
   }
 
   // The equality operator is used by FindPropertiesNeedingUpdate.h for checking
   // if a scroll node has changed.
   bool operator==(const ScrollPaintPropertyNode& o) const {
-    // TODO(pdr): Check main thread scrolling reason equality as well. We do
-    // not yet mark nodes as needing a paint property update on main thread
-    // scrolling reason changes. See: See: https://crbug.com/664672.
     return m_parent == o.m_parent &&
            m_scrollOffsetTranslation == o.m_scrollOffsetTranslation &&
            m_clip == o.m_clip && m_bounds == o.m_bounds &&
            m_userScrollableHorizontal == o.m_userScrollableHorizontal &&
-           m_userScrollableVertical == o.m_userScrollableVertical;
+           m_userScrollableVertical == o.m_userScrollableVertical &&
+           m_threadedScrollingDisabled == o.m_threadedScrollingDisabled &&
+           m_hasBackgroundAttachmentFixedDescendants ==
+               o.m_hasBackgroundAttachmentFixedDescendants;
   }
 #endif
 
  private:
   ScrollPaintPropertyNode(
-      PassRefPtr<ScrollPaintPropertyNode> parent,
+      PassRefPtr<const ScrollPaintPropertyNode> parent,
       PassRefPtr<const TransformPaintPropertyNode> scrollOffsetTranslation,
       IntSize clip,
       IntSize bounds,
       bool userScrollableHorizontal,
-      bool userScrollableVertical)
+      bool userScrollableVertical,
+      bool threadedScrollingDisabled,
+      bool hasBackgroundAttachmentFixedDescendants)

[Xianzhu, 2016/11/17 19:03:04]

Can we use named bit flags to replace the multiple bool parameters? I think
flags are clearer at callsites and can avoid errors of wrong parameters.

[pdr., 2016/11/17 21:01:36]

+1, this looks much better. Done.

       : m_parent(parent),
         m_scrollOffsetTranslation(scrollOffsetTranslation),
         m_clip(clip),
         m_bounds(bounds),
         m_userScrollableHorizontal(userScrollableHorizontal),
         m_userScrollableVertical(userScrollableVertical),
-        m_mainThreadScrollingReasons(0) {
+        m_threadedScrollingDisabled(threadedScrollingDisabled),
+        m_hasBackgroundAttachmentFixedDescendants(
+            hasBackgroundAttachmentFixedDescendants) {
     DCHECK(m_scrollOffsetTranslation->matrix().isIdentityOr2DTranslation());
   }
 
-  RefPtr<ScrollPaintPropertyNode> m_parent;
+  RefPtr<const ScrollPaintPropertyNode> m_parent;
   RefPtr<const TransformPaintPropertyNode> m_scrollOffsetTranslation;
   IntSize m_clip;
   IntSize m_bounds;
-  bool m_userScrollableHorizontal;
-  bool m_userScrollableVertical;
-  MainThreadScrollingReasons m_mainThreadScrollingReasons;
+  bool m_userScrollableHorizontal : 1;
+  bool m_userScrollableVertical : 1;
+  // The following bools are for main thread scrolling reasons.
+  bool m_threadedScrollingDisabled : 1;
+  bool m_hasBackgroundAttachmentFixedDescendants : 1;
   // TODO(pdr): Add an offset for the clip and bounds to the transform.
   // TODO(pdr): Add 2 bits for whether this is a viewport scroll node.
   // TODO(pdr): Add a bit for whether this is affected by page scale.
 };
 
 // Redeclared here to avoid ODR issues.
 // See platform/testing/PaintPrinters.h.
 void PrintTo(const ScrollPaintPropertyNode&, std::ostream*);
 
 }  // namespace blink
 
 #endif  // ScrollPaintPropertyNode_h