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

Source/platform/graphics/ContentLayerDelegate.cpp

Index: Source/platform/graphics/ContentLayerDelegate.cpp
diff --git a/Source/platform/graphics/ContentLayerDelegate.cpp b/Source/platform/graphics/ContentLayerDelegate.cpp
index 657ecb92854104a0c810de448a4d56e21085ef67..ee11c43bd5876140c25da2fa7a60e237d23ec6eb 100644
--- a/Source/platform/graphics/ContentLayerDelegate.cpp
+++ b/Source/platform/graphics/ContentLayerDelegate.cpp
@@ -33,6 +33,7 @@
 #include "platform/geometry/IntRect.h"
 #include "platform/graphics/GraphicsContext.h"
 #include "platform/graphics/paint/DisplayItemList.h"
+#include "platform/graphics/paint/DisplayList.h"
 #include "platform/transforms/AffineTransform.h"
 #include "platform/transforms/TransformationMatrix.h"
 #include "public/platform/WebDisplayItemList.h"
@@ -90,6 +91,16 @@ void ContentLayerDelegate::paintContents(
 
     ASSERT(RuntimeEnabledFeatures::slimmingPaintEnabled());
 
+    if (RuntimeEnabledFeatures::slimmingPaintCompositorLayerizationEnabled()) {
+        // Scrollbars for the root frame stil paint in the old way, and don't have a displayList().
+        if (m_painter->displayList()) {
+            for (unsigned i = 0; i < m_painter->displayList()->size(); i++) {
+                m_painter->displayList()->displayItemInternal(i).appendToWebDisplayItemList(webDisplayItemList);

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

Is it possible that this line changes the order of DisplayItems in the global
DisplayItemList, thus invalidate the indices we saved in the offset of
WebDisplayList on each layer?

Since we'd have to convert DisplayItem to WebDisplayItem, maybe we could let
Layers own the partial WebDisplayItemList? WDYT?

[chrishtr, 2015/07/24 19:27:21]

I think we should end up with representation in which there is exactly one
display list array that everyone on the same thread shares. The copying in this
CL is necessary only before the blink/cc merge.

As for whether there is a bug in this sample implementation...maybe. :)

+            }
+            return;
+        }
+    }
+
     DisplayItemList* displayItemList = m_painter->displayItemList();
     ASSERT(displayItemList);
     displayItemList->setDisplayItemConstructionIsDisabled(
@@ -116,4 +127,14 @@ size_t ContentLayerDelegate::approximateUnsharedMemoryUsage() const
     return m_painter->displayItemList()->approximateUnsharedMemoryUsage();
 }
 
+const WebDisplayList* ContentLayerDelegate::displayList() const
+{
+    return m_painter->displayList();
+}
+
+const WebDisplayItemTransformTree* ContentLayerDelegate::transformTree() const
+{
+    return 0;
+}
+
 } // namespace blink