optimizing layout performance when only transform3d matrix changed by

Source/core/rendering/compositing/RenderLayerCompositor.cpp

Index: Source/core/rendering/compositing/RenderLayerCompositor.cpp
===================================================================
--- Source/core/rendering/compositing/RenderLayerCompositor.cpp	(revision 169401)
+++ Source/core/rendering/compositing/RenderLayerCompositor.cpp	(working copy)
@@ -211,6 +211,7 @@
     , m_needsUpdateCompositingRequirementsState(false)
     , m_isTrackingRepaints(false)
     , m_rootLayerAttachment(RootLayerUnattached)
+    , m_layersChanged(true)
 {
 }
 
@@ -383,6 +384,13 @@
     case CompositingUpdateAfterCanvasContextChange:
         m_needsToUpdateLayerTreeGeometry = true;
         break;
+    case CompositingMinUpdateAfterStyleChange:
+        if (m_layersChanged)

[Ian Vollick, 2014/03/18 11:59:16]

I think this is a layering violation. If I'm understanding this correctly, this
code is saying "if the layers changed the last time we computed compositing
requirements, we need to update the compositing requirements". It seems too late
at that point.

[yaojie.yan, 2014/03/20 07:43:19]

Yes, but my REAL purpose is to add some heuristic information here, if the
composting reasons did not changes for a long time, we will not need to
recomputingCompostingReasons for just transforms3d. I think there is the
tradeoff. Since it is a much overhead to recomputingCompostingReasons with
overlap for overmuch-layers page. Is it worthy to computing a pretty accurate a
GraphicsLayers Tree for just transforms3d case?

On 2014/03/18 11:59:16, Ian Vollick wrote:

+            m_needsToRecomputeCompositingRequirements = true;
+        else
+            m_needsToUpdateLayerTreeGeometry = true;
+        break;
+
     }
 
     m_renderView.frameView()->scheduleAnimation();
@@ -473,6 +481,7 @@
             }
         }
 
+        m_layersChanged = layersChanged;

[Ian Vollick, 2014/03/18 11:59:16]

This value should not persist from update to update.

         if (layersChanged)
             needHierarchyAndGeometryUpdate = true;
     }
@@ -496,7 +505,7 @@
 
         if (childList.isEmpty())
             destroyRootLayer();
-        else
+        else if (m_rootContentLayer)
             m_rootContentLayer->setChildren(childList);
     } else if (needGeometryUpdate) {
         // We just need to do a geometry update. This is only used for position:fixed scrolling;