Add background attachment fixed main thread scrolling reason [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"
+#include "platform/scroll/MainThreadScrollingReason.h"
 #include "wtf/PassRefPtr.h"
 #include "wtf/RefCounted.h"
 #include "wtf/RefPtr.h"
 
 #include <iosfwd>
 
 namespace blink {
 
-// A scroll node contains auxiliary scrolling information for compositor-thread
-// scrolling and includes how far an area can be scrolled, which
-// |TransformPaintPropertyNode| contains the scroll offset, etc.
+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.
+//
+// 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 PassRefPtr<ScrollPaintPropertyNode> create(
-        PassRefPtr<const ScrollPaintPropertyNode> parent,
+        PassRefPtr<ScrollPaintPropertyNode> parent,
         PassRefPtr<const TransformPaintPropertyNode> scrollOffsetTranslation,
         const IntSize& clip,
         const IntSize& bounds,
         bool userScrollableHorizontal,
         bool userScrollableVertical)
     {
         return adoptRef(new ScrollPaintPropertyNode(std::move(parent), std::move(scrollOffsetTranslation), clip, bounds, userScrollableHorizontal, userScrollableVertical));
     }
 
-    void update(PassRefPtr<const ScrollPaintPropertyNode> parent, PassRefPtr<const TransformPaintPropertyNode> scrollOffsetTranslation, const IntSize& clip, const IntSize& bounds, bool userScrollableHorizontal, bool userScrollableVertical)
+    void update(PassRefPtr<ScrollPaintPropertyNode> parent, PassRefPtr<const TransformPaintPropertyNode> scrollOffsetTranslation, const IntSize& clip, const IntSize& bounds, bool userScrollableHorizontal, bool userScrollableVertical)
     {
         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;
     }
 
-    const ScrollPaintPropertyNode* parent() const { return m_parent.get(); }
+    ScrollPaintPropertyNode* parent() const { return m_parent.get(); }
 
     // 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;
+    }
+    bool hasBackgroundAttachmentFixedMainThreadScrollingReason() const
+    {
+        return m_mainThreadScrollingReasons & MainThreadScrollingReason::kHasBackgroundAttachmentFixedObjects;
+    }
+    void setBackgroundAttachmentFixedMainThreadScrollingReason()

[chrishtr, 2016/09/19 17:00:12]

How about:

void addMainThreadScrollingReason(MainThreadScrollingReason reason)
{
  m_mainThreadScrollingReasons |= reason;
}

and

bool hasSpecifiedMainThreadScrollingReason(MainThreadScrollingReason reason)
{
  rreturn m_mainThreadScrollingReasons & reason;
}

This would generalize beyond background-attachment: fixed

[pdr., 2016/09/19 20:25:50]

+1, was going in this direction in the followup patch. Updated to do it here. To
keep the names short and reduce casts, I used the following names:
bool hasMainThreadScrollingReasons(MainThreadScrollingReasons reasons) const
void addMainThreadScrollingReasons(MainThreadScrollingReasons reasons)

+    {
+        m_mainThreadScrollingReasons |= MainThreadScrollingReason::kHasBackgroundAttachmentFixedObjects;
+    }
+
 private:
     ScrollPaintPropertyNode(
-        PassRefPtr<const ScrollPaintPropertyNode> parent,
+        PassRefPtr<ScrollPaintPropertyNode> parent,
         PassRefPtr<const TransformPaintPropertyNode> scrollOffsetTranslation,
         IntSize clip,
         IntSize bounds,
         bool userScrollableHorizontal,
         bool userScrollableVertical)
         : m_parent(parent)
         , m_scrollOffsetTranslation(scrollOffsetTranslation)
         , m_clip(clip)
         , m_bounds(bounds)
         , m_userScrollableHorizontal(userScrollableHorizontal)
         , m_userScrollableVertical(userScrollableVertical)
+        , m_mainThreadScrollingReasons(0)
     {
         DCHECK(m_scrollOffsetTranslation->matrix().isIdentityOr2DTranslation());
     }
 
-    RefPtr<const ScrollPaintPropertyNode> m_parent;
+    RefPtr<ScrollPaintPropertyNode> m_parent;
     RefPtr<const TransformPaintPropertyNode> m_scrollOffsetTranslation;
     IntSize m_clip;
     IntSize m_bounds;
     bool m_userScrollableHorizontal;
     bool m_userScrollableVertical;
-    // TODO(pdr): Add main thread scrolling reasons.
+    MainThreadScrollingReasons m_mainThreadScrollingReasons;
     // 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