Reuse existing paint property node is possible

third_party/WebKit/Source/platform/graphics/paint/TransformPaintPropertyNode.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 TransformPaintPropertyNode_h
 #define TransformPaintPropertyNode_h
 
 #include "platform/PlatformExport.h"
 #include "platform/geometry/FloatPoint3D.h"
 #include "platform/transforms/TransformationMatrix.h"
 #include "wtf/PassRefPtr.h"
 #include "wtf/RefCounted.h"
 #include "wtf/RefPtr.h"
 
 #include <iosfwd>
 
 namespace blink {
 
 // A transform created by a css property such as "transform" or "perspective"
 // along with a reference to the parent TransformPaintPropertyNode, or nullptr
 // for the root.
 class PLATFORM_EXPORT TransformPaintPropertyNode : public RefCounted<TransformPaintPropertyNode> {
 public:
+    struct Value {
+        Value() { }
+        Value(const TransformationMatrix& matrix, const FloatPoint3D& origin) : matrix(matrix), origin(origin) { }
+        bool operator ==(const Value& other) const { return matrix == other.matrix && origin == other.origin; }

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

Nit: no space between operator and ==

[Xianzhu, 2016/07/22 01:14:05]

No more applicable.

+
+        TransformationMatrix matrix;
+        FloatPoint3D origin;
+    };
+
     static PassRefPtr<TransformPaintPropertyNode> create(const TransformationMatrix& matrix, const FloatPoint3D& origin, PassRefPtr<TransformPaintPropertyNode> parent = nullptr)
     {
-        return adoptRef(new TransformPaintPropertyNode(matrix, origin, parent));
+        return adoptRef(new TransformPaintPropertyNode(Value(matrix, origin), parent));
     }
 
-    const TransformationMatrix& matrix() const { return m_matrix; }
-    const FloatPoint3D& origin() const { return m_origin; }
+    // This form is required by PaintPropertyTreeBuilder::updateObjectPaintProperties().
+    static PassRefPtr<TransformPaintPropertyNode> create(const Value& value, PassRefPtr<TransformPaintPropertyNode> parent)
+    {
+        return adoptRef(new TransformPaintPropertyNode(value, parent));
+    }
+
+    const Value& value() const { return m_value; }
+    const TransformationMatrix& matrix() const { return m_value.matrix; }
+    const FloatPoint3D& origin() const { return m_value.origin; }
 
     // Parent transform that this transform is relative to, or nullptr if this
     // is the root transform.
     TransformPaintPropertyNode* parent() const { return m_parent.get(); }
 
+    // Moves this node and its subtrees under another parent.
+    void setParent(PassRefPtr<TransformPaintPropertyNode> parent) { m_parent = parent; }

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

What do you think of restricting setters to PaintPropertyTreeBuilder?

private:
    friend class PaintPropertyTreeBuilder; // Setter should only be used by
PaintPropertyTreeBuilder.
    // Moves this node and its children under another parent.
    void setParent(PassRefPtr<TransformPaintPropertyNode> parent) { m_parent =
parent; }

[Xianzhu, 2016/07/22 01:14:05]

Changed this to update() method. I think 'const' is enough to distinguish the
different access privileges. Using friend also opens up other private things to
PaintPropertyTreeBuilder.

+
 private:
+    TransformPaintPropertyNode(const Value& value, PassRefPtr<TransformPaintPropertyNode> parent)
+        : m_value(value), m_parent(parent) { }
 
-    TransformPaintPropertyNode(const TransformationMatrix& matrix, const FloatPoint3D& origin, PassRefPtr<TransformPaintPropertyNode> parent)
-        : m_matrix(matrix), m_origin(origin), m_parent(parent) { }
-
-    const TransformationMatrix m_matrix;
-    const FloatPoint3D m_origin;
+    Value m_value;
     RefPtr<TransformPaintPropertyNode> m_parent;
 };
 
 // Redeclared here to avoid ODR issues.
 // See platform/testing/PaintPrinters.h.
 void PrintTo(const TransformPaintPropertyNode&, std::ostream*);
 
 } // namespace blink
 
 #endif // TransformPaintPropertyNode_h