PaintChunk::id

third_party/WebKit/Source/platform/graphics/paint/ScopedPaintChunkProperties.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 ScopedPaintChunkProperties_h
 #define ScopedPaintChunkProperties_h
 
+#include "platform/graphics/paint/DisplayItem.h"
+#include "platform/graphics/paint/PaintChunk.h"
 #include "platform/graphics/paint/PaintChunkProperties.h"
 #include "platform/graphics/paint/PaintController.h"
 #include "wtf/Allocator.h"
 #include "wtf/Noncopyable.h"
 
 namespace blink {
 
 class ScopedPaintChunkProperties {
     DISALLOW_NEW_EXCEPT_PLACEMENT_NEW();
     WTF_MAKE_NONCOPYABLE(ScopedPaintChunkProperties);
 public:
-    ScopedPaintChunkProperties(PaintController& paintController, const PaintChunkProperties& properties)
+    ScopedPaintChunkProperties(PaintController& paintController, const DisplayItemClient& client, DisplayItem::Type type, const PaintChunkProperties& properties)
         : m_paintController(paintController)
         , m_previousProperties(paintController.currentPaintChunkProperties())
     {
-        m_paintController.updateCurrentPaintChunkProperties(properties);
+        PaintChunk::Id id(client, type);
+        m_paintController.updateCurrentPaintChunkProperties(&id, properties);
     }
 
+    // Omits the type parameter, in case that the client creates only one PaintChunkProperties node during each painting.
+    ScopedPaintChunkProperties(PaintController& paintController, const DisplayItemClient& client, const PaintChunkProperties& properties)
+        : ScopedPaintChunkProperties(paintController, client, DisplayItem::UninitializedType, properties)
+    { }
+
     ~ScopedPaintChunkProperties()
     {
-        m_paintController.updateCurrentPaintChunkProperties(m_previousProperties);
+        // We should not return to the previous id, because that may cause a new chunk to use
+        // the same id as that of the previous chunk before this ScopedPaintChunkProperties.
+        // The painter should create another scope of paint properties with new id, or the
+        // new chunk will have no id and will not match any old chunk and will be treated as
+        // fully invalidated for rasterization.
+        m_paintController.updateCurrentPaintChunkProperties(nullptr, m_previousProperties);

[chrishtr, 2016/07/19 17:27:52]

Will this sometimes create extra empty paint chunks if there is another
ScopedPaintChunkProperties immediately following?

[Xianzhu, 2016/07/19 21:57:48]

PaintChunker checks change of PaintChunkProperties to determine if new chunk is
needed. The above change won't change how PaintChunker works.

As PaintChunker creates chunks in incrementDisplayItemIndex() only, the above
call won't cause empty chunks.

     }
 
 private:
     PaintController& m_paintController;
     PaintChunkProperties m_previousProperties;
 };
 
 } // namespace blink
 
 #endif // ScopedPaintChunkProperties_h