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/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);
+        DisplayItem::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.

[pdr., 2016/07/14 22:22:06]

Can this happen when we are not skipping the cache? If not, can PaintController
be responsible for handling the skipping cache logic?

[Xianzhu, 2016/07/14 23:03:24]

Skipping cache will cause chunk with null id, causing the chunk is treated as
new. However, a chunk with a null id doesn't require skipping cache. The content
of the chunk can still use cache, but the chunk itself will be treated as newly
created for layerization and rasterization invalidation.

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