Slimming Paint phase 2 compositing algorithm plumbing & skeleton display list API.

Source/platform/graphics/paint/DisplayItemTransformTreeBuilder.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 DisplayItemTransformTreeBuilder_h
 #define DisplayItemTransformTreeBuilder_h
 
 #include "platform/PlatformExport.h"
 #include "platform/geometry/FloatSize.h"
+#include "platform/graphics/paint/DisplayItemList.h"
 #include "wtf/OwnPtr.h"
 #include "wtf/PassOwnPtr.h"
 #include "wtf/Vector.h"
 
 namespace blink {
 
 class DisplayItem;
+class DisplayItemList;
 class DisplayItemTransformTree;
+class WebDisplayList;
 
 class PLATFORM_EXPORT DisplayItemTransformTreeBuilder {
 public:
     DisplayItemTransformTreeBuilder();
     ~DisplayItemTransformTreeBuilder();
 
     // Detach the built transform tree.
     // This can be used to construct a WebDisplayItemTransformTree.
     PassOwnPtr<DisplayItemTransformTree> releaseTransformTree();
 
+    void build(const DisplayItemList& displayList, const DisplayListDiff&);

[weiliangc, 2015/07/24 19:17:15]

Would it make sense to make DisplayItemTransformTreeBuilder look more like
DisplayListCompositngBuilder?
Such as, set const & to displayList and displayListDiff in constructor, build(),
and hide and processDisplayItem() function?

[chrishtr, 2015/07/24 19:27:22]

Common patterns good yes. :)

+
     // Process another display item from the list.
     void processDisplayItem(const DisplayItem&);
 
 private:
     struct CurrentTransformNodeData {
         CurrentTransformNodeData(size_t nodeIndex, const FloatSize& offsetFromOrigin)
             : transformNode(nodeIndex), offset(offsetFromOrigin), ignoredBeginCount(0) { }
 
         // Index of the current transform node.
         size_t transformNode;
@@ skipping 20 matching lines @@
 
     OwnPtr<DisplayItemTransformTree> m_transformTree;
     Vector<CurrentTransformNodeData, 16> m_currentTransformNodeStack;
     size_t m_rangeBeginIndex;
     size_t m_currentIndex;
 };
 
 } // namespace
 
 #endif // DisplayItemTransformTreeBuilder_h