Reuse existing paint property node is possible

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

 // Copyright 2015 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 ClipPaintPropertyNode_h
 #define ClipPaintPropertyNode_h
 
 #include "platform/PlatformExport.h"
 #include "platform/geometry/FloatRoundedRect.h"
 #include "platform/graphics/paint/TransformPaintPropertyNode.h"
 #include "wtf/PassRefPtr.h"
 #include "wtf/RefCounted.h"
 #include "wtf/RefPtr.h"
 
 #include <iosfwd>
 
 namespace blink {
 
 // A clip rect created by a css property such as "overflow" or "clip".
 // Along with a refernce to the transform space the clip rect is based on,
 // and an (optional) parent ClipPaintPropertyNode for inherited clips.
 class PLATFORM_EXPORT ClipPaintPropertyNode : public RefCounted<ClipPaintPropertyNode> {
 public:
+    using Value = FloatRoundedRect;

[pdr., 2016/07/21 21:34:07]

Can a refptr to the local transform space be included in the value so we don't
need to special-case local transform space?

+
     static PassRefPtr<ClipPaintPropertyNode> create(
         PassRefPtr<TransformPaintPropertyNode> localTransformSpace,
         const FloatRoundedRect& clipRect,
         PassRefPtr<ClipPaintPropertyNode> parent = nullptr)
     {
         return adoptRef(new ClipPaintPropertyNode(localTransformSpace, clipRect, parent));
     }
 
+    // This form is required by PaintPropertyTreeBuilder::updateObjectPaintProperties().
+    static PassRefPtr<ClipPaintPropertyNode> create(const Value& value, PassRefPtr<ClipPaintPropertyNode> parent)
+    {
+        return adoptRef(new ClipPaintPropertyNode(nullptr, value, parent));
+    }
+
     const TransformPaintPropertyNode* localTransformSpace() const { return m_localTransformSpace.get(); }
+    const Value& value() const { return m_clipRect; }
     const FloatRoundedRect& clipRect() const { return m_clipRect; }
 
     // Reference to inherited clips, or nullptr if this is the only clip.
     const ClipPaintPropertyNode* parent() const { return m_parent.get(); }
 
+    // Moves this node and its subtrees under another parent.
+    void setParent(PassRefPtr<ClipPaintPropertyNode> parent) { m_parent = parent; }
+
+    // This is separate from the create() method for child node for two purposes:
+    // 1. to let the method have the same parameter list as the method of other paint
+    //    property node classes, so that they can be used in the same template;

[pdr., 2016/07/21 21:34:06]

Nit: ; -> .

+    // 2. to allow to reuse an existing node in a new tree.
+    void setLocalTransformSpace(PassRefPtr<TransformPaintPropertyNode> localTransformSpace) { m_localTransformSpace = localTransformSpace; }
+
 private:
     ClipPaintPropertyNode(PassRefPtr<TransformPaintPropertyNode> localTransformSpace, const FloatRoundedRect& clipRect, PassRefPtr<ClipPaintPropertyNode> parent)
         : m_localTransformSpace(localTransformSpace), m_clipRect(clipRect), m_parent(parent) { }
 
     RefPtr<TransformPaintPropertyNode> m_localTransformSpace;
     const FloatRoundedRect m_clipRect;
     RefPtr<ClipPaintPropertyNode> m_parent;
 };
 
 // Redeclared here to avoid ODR issues.
 // See platform/testing/PaintPrinters.h.
 void PrintTo(const ClipPaintPropertyNode&, std::ostream*);
 
 } // namespace blink
 
 #endif // ClipPaintPropertyNode_h