Bug 1219020 - Don't do layer tree comparisons for inactive layer trees that have changed layers since we'll invalidate it all anyway. r=roc

--HG--
extra : rebase_source : 659233e99a8c84a7d4a097aed06adb243bd10955

layout/base/FrameLayerBuilder.cpp

@@ -4432,10 +4432,12 @@ FrameLayerBuilder::AddPaintedDisplayItem(PaintedLayerData* aLayerData,
   RefPtr<BasicLayerManager> tempManager;
   nsIntRect intClip;
   bool hasClip = false;
+  bool havePreviousData = false;
   if (aLayerState != LAYER_NONE) {
     DisplayItemData *data = GetDisplayItemDataForManager(aItem, layer->Manager());
     if (data) {
       tempManager = data->mInactiveManager;
+      havePreviousData = !!data->mGeometry;
     }
     if (!tempManager) {
       tempManager = new BasicLayerManager(BasicLayerManager::BLM_INACTIVE);
@@ -4474,7 +4476,13 @@ FrameLayerBuilder::AddPaintedDisplayItem(PaintedLayerData* aLayerData,
         layerBuilder->DidBeginRetainedLayerTransaction(tempManager);
       }
 
-      UniquePtr<LayerProperties> props(LayerProperties::CloneFrom(tempManager->GetRoot()));
+      // If we have previous data for this item, then we need to track changes
+      // to the layer tree and invalidate them. If we don't have any previous
+      // data then ComputeGeometryChangeForItem will invalidate the item's bounds.
+      UniquePtr<LayerProperties> props;
+      if (havePreviousData) {
+        props = LayerProperties::CloneFrom(tempManager->GetRoot());
+      }
       RefPtr<Layer> tmpLayer =
         aItem->BuildLayer(mDisplayListBuilder, tempManager, ContainerLayerParameters());
       // We have no easy way of detecting if this transaction will ever actually get finished.
@@ -4517,29 +4525,31 @@ FrameLayerBuilder::AddPaintedDisplayItem(PaintedLayerData* aLayerData,
       }
 #endif
 
-      nsIntPoint offset = GetLastPaintOffset(layer) - GetTranslationForPaintedLayer(layer);
-      props->MoveBy(-offset);
-      nsIntRegion invalid = props->ComputeDifferences(tmpLayer, nullptr);
-      if (aLayerState == LAYER_SVG_EFFECTS) {
-        invalid = nsSVGIntegrationUtils::AdjustInvalidAreaForSVGEffects(aItem->Frame(),
-                                                                        aItem->ToReferenceFrame(),
-                                                                        invalid);
-      }
-      if (!invalid.IsEmpty()) {
+      if (props) {
+        nsIntPoint offset = GetLastPaintOffset(layer) - GetTranslationForPaintedLayer(layer);
+        props->MoveBy(-offset);
+        nsIntRegion invalid = props->ComputeDifferences(tmpLayer, nullptr);
+        if (aLayerState == LAYER_SVG_EFFECTS) {
+          invalid = nsSVGIntegrationUtils::AdjustInvalidAreaForSVGEffects(aItem->Frame(),
+                                                                          aItem->ToReferenceFrame(),
+                                                                          invalid);
+        }
+        if (!invalid.IsEmpty()) {
 #ifdef MOZ_DUMP_PAINTING
-        if (nsLayoutUtils::InvalidationDebuggingIsEnabled()) {
-          printf_stderr("Inactive LayerManager(%p) for display item %s(%p) has an invalid region - invalidating layer %p\n", tempManager.get(), aItem->Name(), aItem->Frame(), layer);
-        }
+          if (nsLayoutUtils::InvalidationDebuggingIsEnabled()) {
+             printf_stderr("Inactive LayerManager(%p) for display item %s(%p) has an invalid region - invalidating layer %p\n", tempManager.get(), aItem->Name(), aItem->Frame(), layer);
+          }
 #endif
-        invalid.ScaleRoundOut(paintedData->mXScale, paintedData->mYScale);
+          invalid.ScaleRoundOut(paintedData->mXScale, paintedData->mYScale);
 
-        if (hasClip) {
-          invalid.And(invalid, intClip);
+          if (hasClip) {
+            invalid.And(invalid, intClip);
+          }
+
+          InvalidatePostTransformRegion(layer, invalid,
+                                        GetTranslationForPaintedLayer(layer),
+                                        paintedData);
         }
-
-        InvalidatePostTransformRegion(layer, invalid,
-                                      GetTranslationForPaintedLayer(layer),
-                                      paintedData);
       }
     }
     ClippedDisplayItem* cdi =