Bug 1221842 - Don't reallocate DLBI geometry objects if nothing has changed. r=roc

layout/base/FrameLayerBuilder.cpp

@@ -177,8 +177,11 @@ FrameLayerBuilder::DisplayItemData::EndUpdate(nsAutoPtr<nsDisplayItemGeometry> a
 {
   MOZ_RELEASE_ASSERT(mLayer);
   MOZ_ASSERT(mItem);
+  MOZ_ASSERT(mGeometry || aGeometry);
 
+  if (aGeometry) {
     mGeometry = aGeometry;
+  }
   mClip = mItem->GetClip();
   mFrameListChanges.Clear();
 
@@ -4356,7 +4359,7 @@ FrameLayerBuilder::ComputeGeometryChangeForItem(DisplayItemData* aData)
 
   PaintedLayerItemsEntry* entry = mPaintedLayerItems.GetEntry(paintedLayer);
 
-  nsAutoPtr<nsDisplayItemGeometry> geometry(item->AllocateGeometry(mDisplayListBuilder));
+  nsAutoPtr<nsDisplayItemGeometry> geometry;
 
   PaintedDisplayItemLayerUserData* layerData =
     static_cast<PaintedDisplayItemLayerUserData*>(aData->mLayer->GetUserData(&gPaintedDisplayItemLayerUserData));
@@ -4372,7 +4375,7 @@ FrameLayerBuilder::ComputeGeometryChangeForItem(DisplayItemData* aData)
   bool notifyRenderingChanged = true;
   if (!aData->mGeometry) {
     // This item is being added for the first time, invalidate its entire area.
-    //TODO: We call GetGeometry again in AddPaintedDisplayItem, we should reuse this.
+    geometry = item->AllocateGeometry(mDisplayListBuilder);
     combined = clip.ApplyNonRoundedIntersection(geometry->ComputeInvalidationRegion());
 #ifdef MOZ_DUMP_PAINTING
     if (nsLayoutUtils::InvalidationDebuggingIsEnabled()) {
@@ -4380,7 +4383,8 @@ FrameLayerBuilder::ComputeGeometryChangeForItem(DisplayItemData* aData)
     }
 #endif
   } else if (aData->mIsInvalid || (item->IsInvalid(invalid) && invalid.IsEmpty())) {
-    // Either layout marked item as needing repainting, invalidate the entire old and new areas.
+    // Layout marked item/frame as needing repainting (without an explicit rect), invalidate the entire old and new areas.
+    geometry = item->AllocateGeometry(mDisplayListBuilder);
     combined = aData->mClip.ApplyNonRoundedIntersection(aData->mGeometry->ComputeInvalidationRegion());
     combined.MoveBy(shift);
     combined.Or(combined, clip.ApplyNonRoundedIntersection(geometry->ComputeInvalidationRegion()));
@@ -4394,8 +4398,10 @@ FrameLayerBuilder::ComputeGeometryChangeForItem(DisplayItemData* aData)
     // repainted.
 
     const nsTArray<nsIFrame*>& changedFrames = aData->GetFrameListChanges();
+    aData->mGeometry->MoveBy(shift);
+    item->ComputeInvalidationRegion(mDisplayListBuilder, aData->mGeometry, &combined);
 
-    // We have an optimization to cache the drawing background-attachment: fixed canvas
+    // We have an optimization to cache the drawing of background-attachment: fixed canvas
     // background images so we can scroll and just blit them when they are flattened into
     // the same layer as scrolling content. NotifyRenderingChanged is only used to tell
     // the canvas bg image item to purge this cache. We want to be careful not to accidentally
@@ -4404,16 +4410,16 @@ FrameLayerBuilder::ComputeGeometryChangeForItem(DisplayItemData* aData)
     // AddOffsetAndComputeDifference is the only thing that will invalidate we skip the
     // NotifyRenderingChanged call (ComputeInvalidationRegion for background images also calls
     // NotifyRenderingChanged if anything changes).
-    if (aData->mGeometry->ComputeInvalidationRegion() == geometry->ComputeInvalidationRegion() &&
-        aData->mClip == clip && invalid.IsEmpty() && changedFrames.Length() == 0) {
+    if (!combined.IsEmpty()) {
+      geometry = item->AllocateGeometry(mDisplayListBuilder);
+    } else if (aData->mClip == clip && invalid.IsEmpty() && changedFrames.Length() == 0) {
       notifyRenderingChanged = false;
     }
-
-    aData->mGeometry->MoveBy(shift);
-    item->ComputeInvalidationRegion(mDisplayListBuilder, aData->mGeometry, &combined);
     aData->mClip.AddOffsetAndComputeDifference(entry->mCommonClipCount,
                                                shift, aData->mGeometry->ComputeInvalidationRegion(),
-                                               clip, entry->mLastCommonClipCount, geometry->ComputeInvalidationRegion(),
+                                               clip, entry->mLastCommonClipCount,
+                                               geometry ? geometry->ComputeInvalidationRegion() :
+                                                          aData->mGeometry->ComputeInvalidationRegion(),
                                                &combined);
 
     // Add in any rect that the frame specified