Factor PaintArtifact out of DisplayItemList.

third_party/WebKit/Source/platform/graphics/paint/PaintArtifact.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 PaintArtifact_h
+#define PaintArtifact_h
+
+#include "platform/PlatformExport.h"
+#include "platform/graphics/paint/DisplayItems.h"
+#include "platform/graphics/paint/PaintChunk.h"
+#include "wtf/Vector.h"
+
+namespace blink {
+
+class GraphicsContext;
+class WebDisplayItemList;
+
+// The output of painting, consisting of a series of drawings partitioned into
+// discontiguous chunks with a common set of paint properties (i.e. associated

[wkorman, 2015/10/09 04:45:50]

Does the order of chunks in the vector matter / is it consistent? Seems worth
stating either way.

+// with the same transform, clip, effects, etc.).
+//
+// It represents a particular state of the world, and should be immutable
+// (const) to most of its users.
+class PLATFORM_EXPORT PaintArtifact {
+public:
+    PaintArtifact();
+    ~PaintArtifact();
+
+    bool isEmpty() const { return m_displayItems.isEmpty(); }
+
+    DisplayItems& displayItems() { return m_displayItems; }
+    const DisplayItems& displayItems() const { return m_displayItems; }
+
+    Vector<PaintChunk>& paintChunks() { return m_paintChunks; }
+    const Vector<PaintChunk>& paintChunks() const { return m_paintChunks; }
+
+    // Resets to an empty paint artifact.
+    void reset();
+
+    // Updates the artifact with complete display items and chunks.
+    // This swaps out of the display items, making it empty.
+    // This will be more efficient if you pass an rvalue for updatedPaintChunks
+    // to avoid a copy.
+    // TODO(jbroman): Clean this up once std::move is legal in Blink.
+    void update(DisplayItems& updatedDisplayItems, Vector<PaintChunk> updatedPaintChunks);

[pdr., 2015/10/09 03:57:51]

I think it would be best to leave this in the class that performs the merge
algorithm since the caller basically needs to know everything this function
does.

[jbroman, 2015/10/13 18:20:56]

I waffled on this point, so I'll mail you a CL to change this.

+
+    // Returns the approximate memory usage, excluding memory likely to be
+    // shared with the embedder after copying to WebDisplayItemList.
+    size_t approximateUnsharedMemoryUsage() const;
+
+    // Draws the paint artifact to a GraphicsContext.
+    void replay(GraphicsContext&) const;
+
+    // Writes the paint artifact into a WebDisplayItemList.
+    void appendToWebDisplayItemList(WebDisplayItemList*) const;
+
+private:
+    DisplayItems m_displayItems;
+    Vector<PaintChunk> m_paintChunks;
+};
+
+} // namespace blink
+
+#endif // PaintArtifact_h