Bug 1429932 - Part 6: Attempt to skip Layer building if the display list hasn't changed. r=mstange

MozReview-Commit-ID: 1kBRIVteNb1

layout/base/nsLayoutUtils.cpp

@@ -3985,6 +3985,9 @@ nsLayoutUtils::PaintFrame(gfxContext* aRenderingContext, nsIFrame* aFrame,
   if (aFlags & PaintFrameFlags::PAINT_COMPRESSED) {
     flags |= nsDisplayList::PAINT_COMPRESSED;
   }
+  if (updateState == PartialUpdateResult::NoChange) {
+    flags |= nsDisplayList::PAINT_IDENTICAL_DISPLAY_LIST;
+  }
 
   TimeStamp paintStart = TimeStamp::Now();
   RefPtr<LayerManager> layerManager

layout/painting/nsDisplayList.cpp

@@ -2612,24 +2612,6 @@ already_AddRefed<LayerManager> nsDisplayList::PaintRoot(nsDisplayListBuilder* aB
     }
   }
 
-  // Store the existing layer builder to reinstate it on return.
-  FrameLayerBuilder *oldBuilder = layerManager->GetLayerBuilder();
-  FrameLayerBuilder *layerBuilder = BuildLayers(aBuilder, layerManager,
-                                                aFlags, widgetTransaction);
-
-  if (!layerBuilder) {
-    layerManager->SetUserData(&gLayerManagerLayerBuilder, oldBuilder);
-    return nullptr;
-  }
-
-  if (widgetTransaction ||
-      // SVG-as-an-image docs don't paint as part of the retained layer tree,
-      // but they still need the invalidation state bits cleared in order for
-      // invalidation for CSS/SMIL animation to work properly.
-      (document && document->IsBeingUsedAsImage())) {
-    frame->ClearInvalidationStateBits();
-  }
-
   bool temp = aBuilder->SetIsCompositingCheap(layerManager->IsCompositingCheap());
   LayerManager::EndTransactionFlags flags = LayerManager::END_DEFAULT;
   if (layerManager->NeedsWidgetInvalidation()) {
@@ -2644,25 +2626,53 @@ already_AddRefed<LayerManager> nsDisplayList::PaintRoot(nsDisplayListBuilder* aB
     }
   }
 
-  // If this is the content process, we ship plugin geometry updates over with layer
-  // updates, so calculate that now before we call EndTransaction.
-  nsRootPresContext* rootPresContext = presContext->GetRootPresContext();
-  if (rootPresContext && XRE_IsContentProcess()) {
-    if (aBuilder->WillComputePluginGeometry()) {
-      rootPresContext->ComputePluginGeometryUpdates(aBuilder->RootReferenceFrame(), aBuilder, this);
-    }
-    // The layer system caches plugin configuration information for forwarding
-    // with layer updates which needs to get set during reflow. This must be
-    // called even if there are no windowed plugins in the page.
-    rootPresContext->CollectPluginGeometryUpdates(layerManager);
-  }
-
   MaybeSetupTransactionIdAllocator(layerManager, presContext);
 
-  layerManager->EndTransaction(FrameLayerBuilder::DrawPaintedLayer,
-                               aBuilder, flags);
+  // Store the existing layer builder to reinstate it on return.
+  FrameLayerBuilder *oldBuilder = layerManager->GetLayerBuilder();
+  FrameLayerBuilder *layerBuilder = nullptr;
+
+  bool sent = false;
+  if (aFlags & PAINT_IDENTICAL_DISPLAY_LIST) {
+    sent = layerManager->EndEmptyTransaction(flags);
+  }
+
+  if (!sent) {
+    layerBuilder = BuildLayers(aBuilder, layerManager,
+                               aFlags, widgetTransaction);
+
+    if (!layerBuilder) {
+      layerManager->SetUserData(&gLayerManagerLayerBuilder, oldBuilder);
+      return nullptr;
+    }
+
+    // If this is the content process, we ship plugin geometry updates over with layer
+    // updates, so calculate that now before we call EndTransaction.
+    nsRootPresContext* rootPresContext = presContext->GetRootPresContext();
+    if (rootPresContext && XRE_IsContentProcess()) {
+      if (aBuilder->WillComputePluginGeometry()) {
+        rootPresContext->ComputePluginGeometryUpdates(aBuilder->RootReferenceFrame(), aBuilder, this);
+      }
+      // The layer system caches plugin configuration information for forwarding
+      // with layer updates which needs to get set during reflow. This must be
+      // called even if there are no windowed plugins in the page.
+      rootPresContext->CollectPluginGeometryUpdates(layerManager);
+    }
+
+    layerManager->EndTransaction(FrameLayerBuilder::DrawPaintedLayer,
+                                 aBuilder, flags);
+    layerBuilder->DidEndTransaction();
+  }
+
+  if (widgetTransaction ||
+      // SVG-as-an-image docs don't paint as part of the retained layer tree,
+      // but they still need the invalidation state bits cleared in order for
+      // invalidation for CSS/SMIL animation to work properly.
+      (document && document->IsBeingUsedAsImage())) {
+    frame->ClearInvalidationStateBits();
+  }
+
   aBuilder->SetIsCompositingCheap(temp);
-  layerBuilder->DidEndTransaction();
 
   if (document && widgetTransaction) {
     TriggerPendingAnimations(document, layerManager->GetAnimationReadyTime());

layout/painting/nsDisplayList.h

@@ -3025,7 +3025,8 @@ public:
     PAINT_USE_WIDGET_LAYERS = 0x01,
     PAINT_EXISTING_TRANSACTION = 0x04,
     PAINT_NO_COMPOSITE = 0x08,
-    PAINT_COMPRESSED = 0x10
+    PAINT_COMPRESSED = 0x10,
+    PAINT_IDENTICAL_DISPLAY_LIST = 0x20
   };
   already_AddRefed<LayerManager> PaintRoot(nsDisplayListBuilder* aBuilder,
                                            gfxContext* aCtx,