Implement the framework for the paint property hierarchy

third_party/WebKit/Source/platform/graphics/paint/TransformPaintProperty.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 TransformPaintProperty_h
+#define TransformPaintProperty_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 TransformPaintProperty, or nullptr for
+// the root.
+class PLATFORM_EXPORT TransformPaintProperty : public RefCounted<TransformPaintProperty> {

[jbroman, 2015/10/07 15:22:22]

nit: Having "node" in this would suggest hierarchy more to me, like
"PaintTransformNode", but I don't want to bikeshed this too much.

[pdr., 2015/10/07 20:19:11]

Changed to TransformPaintPropertyNode. I wanted to keep the name "PaintProperty"
here to minimize confusion when layout folks see this hanging off their tree.

+public:
+
+    // Used for disambiguating multiple transforms of the same type.
+    enum Type {
+        Transform,
+        Perspective

[jbroman, 2015/10/07 15:22:22]

Hmm. Ideally this distinction wouldn't leak into platform/ explicitly. Can we
contain this to core/? Does platform/ use it for anything?

[pdr., 2015/10/07 20:19:11]

We can remove this for now, but it may be needed (as an opaque id) to support
subsequences in the future.

+    };
+
+    TransformPaintProperty(const Type type, const TransformationMatrix& matrix, const FloatPoint3D& origin, PassRefPtr<TransformPaintProperty> parent = nullptr)

[jbroman, 2015/10/07 15:22:22]

nit: taking arguments by const value is weird; just "Type" works (you wouldn't
take "const int")

[pdr., 2015/10/07 20:19:11]

Fixed. For some reason this reminded me of the awesome MPAA piracy campaign "You
wouldn't download a car" https://pbs.twimg.com/media/A-DoMcjCMAA8rr9.jpg.

+        : m_type(type), m_matrix(matrix), m_origin(origin), m_parent(parent) { }
+
+    Type type() const { return m_type; }
+    const TransformationMatrix& matrix() const { return m_matrix; }
+    const FloatPoint3D& origin() const { return m_origin; }
+
+    // Parent transform that this transform is relative to, or nullptr if this
+    // is the root transform.
+    const TransformPaintProperty* parent() const { return m_parent.get(); }
+
+private:
+    const Type m_type;
+    const TransformationMatrix m_matrix;
+    const FloatPoint3D m_origin;
+    RefPtr<TransformPaintProperty> m_parent;
+};
+
+// Redeclared here to avoid ODR issues.
+// See platform/testing/PaintPrinters.h.
+void PrintTo(const TransformPaintProperty&, std::ostream*);
+
+} // namespace blink
+
+#endif // TransformPaintProperty_h