Bug 637822: Translate invalidated content by the offset at which it was made valid. r=roc a=b

layout/base/FrameLayerBuilder.cpp

@@ -108,6 +108,22 @@ static void DestroyRegion(void* aPropertyValue)
  */
 NS_DECLARE_FRAME_PROPERTY(ThebesLayerInvalidRegionProperty, DestroyRegion)
 
+static void DestroyPoint(void* aPropertyValue)
+{
+  delete static_cast<nsPoint*>(aPropertyValue);
+}
+
+/**
+ * The valid content in our child ThebesLayers is defined relative to
+ * the offset from this frame to its active scroll root, mapped back
+ * by the ThebesLayer's inverse transform.  Since we accumulate the
+ * region invalidated between last-paint and next-paint, and because
+ * the offset of this frame to its active root may change during that
+ * period, we save the offset at last-paint in this property and use
+ * it to invalidate at next-paint.
+ */
+NS_DECLARE_FRAME_PROPERTY(ThebesLayerLastPaintOffsetProperty, DestroyPoint)
+
 /**
  * This is a helper object used to build up the layer children for
  * a ContainerLayer.
@@ -533,6 +549,35 @@ FrameLayerBuilder::WillEndTransaction(LayerManager* aManager)
                "Some frame must have a layer!");
 }
 
+static void
+SetHasContainerLayer(nsIFrame* aFrame, nsPoint aOffsetToRoot)
+{
+  aFrame->AddStateBits(NS_FRAME_HAS_CONTAINER_LAYER);
+  for (nsIFrame* f = aFrame;
+       f && !(f->GetStateBits() & NS_FRAME_HAS_CONTAINER_LAYER_DESCENDANT);
+       f = nsLayoutUtils::GetCrossDocParentFrame(f)) {
+    f->AddStateBits(NS_FRAME_HAS_CONTAINER_LAYER_DESCENDANT);
+  }
+
+  FrameProperties props = aFrame->Properties();
+  nsPoint* lastPaintOffset = static_cast<nsPoint*>
+    (props.Get(ThebesLayerLastPaintOffsetProperty()));
+  if (lastPaintOffset) {
+    *lastPaintOffset = aOffsetToRoot;
+  } else {
+    props.Set(ThebesLayerLastPaintOffsetProperty(), new nsPoint(aOffsetToRoot));
+  }
+}
+
+static void
+SetNoContainerLayer(nsIFrame* aFrame)
+{
+  FrameProperties props = aFrame->Properties();
+  props.Delete(ThebesLayerInvalidRegionProperty());
+  props.Delete(ThebesLayerLastPaintOffsetProperty());
+  aFrame->RemoveStateBits(NS_FRAME_HAS_CONTAINER_LAYER);
+}
+
 /* static */ PLDHashOperator
 FrameLayerBuilder::UpdateDisplayItemDataForFrame(nsPtrHashKey<nsIFrame>* aEntry,
                                                  void* aUserArg)
@@ -555,8 +600,7 @@ FrameLayerBuilder::UpdateDisplayItemDataForFrame(nsPtrHashKey<nsIFrame>* aEntry,
     // is DidEndTransaction, which would recreate the user data
     // anyway.
     InternalDestroyDisplayItemData(f, prop, PR_FALSE);
-    props.Delete(ThebesLayerInvalidRegionProperty());
-    f->RemoveStateBits(NS_FRAME_HAS_CONTAINER_LAYER);
+    SetNoContainerLayer(f);
     return PL_DHASH_REMOVE;
   }
 
@@ -573,8 +617,7 @@ FrameLayerBuilder::UpdateDisplayItemDataForFrame(nsPtrHashKey<nsIFrame>* aEntry,
       props.Set(ThebesLayerInvalidRegionProperty(), new nsRegion());
     }
   } else {
-    props.Delete(ThebesLayerInvalidRegionProperty());
-    f->RemoveStateBits(NS_FRAME_HAS_CONTAINER_LAYER);
+    SetNoContainerLayer(f);
   }
 
   // We need to remove and re-add the DisplayItemDataProperty in
@@ -1505,17 +1548,6 @@ ContainerState::Finish(PRUint32* aTextContentFlags)
   *aTextContentFlags = textContentFlags;
 }
 
-static void
-SetHasContainerLayer(nsIFrame* aFrame)
-{
-  aFrame->AddStateBits(NS_FRAME_HAS_CONTAINER_LAYER);
-  for (nsIFrame* f = aFrame;
-       f && !(f->GetStateBits() & NS_FRAME_HAS_CONTAINER_LAYER_DESCENDANT);
-       f = nsLayoutUtils::GetCrossDocParentFrame(f)) {
-    f->AddStateBits(NS_FRAME_HAS_CONTAINER_LAYER_DESCENDANT);
-  }
-}
-
 already_AddRefed<ContainerLayer>
 FrameLayerBuilder::BuildContainerLayerFor(nsDisplayListBuilder* aBuilder,
                                           LayerManager* aManager,
@@ -1566,10 +1598,14 @@ FrameLayerBuilder::BuildContainerLayerFor(nsDisplayListBuilder* aBuilder,
           DisplayItemData(containerLayer, containerDisplayItemKey));
     }
 
+    nsPoint* offsetAtLastPaint = static_cast<nsPoint*>
+      (props.Get(ThebesLayerLastPaintOffsetProperty()));
+    nsPoint currentOffset = aBuilder->ToReferenceFrame(aContainerFrame);
+
     nsRegion* invalidThebesContent(static_cast<nsRegion*>
       (props.Get(ThebesLayerInvalidRegionProperty())));
     if (invalidThebesContent) {
-      nsPoint offset = aBuilder->ToReferenceFrame(aContainerFrame);
+      nsPoint offset = offsetAtLastPaint ? *offsetAtLastPaint : currentOffset;
       invalidThebesContent->MoveBy(offset);
       state.SetInvalidThebesContent(invalidThebesContent->
         ToOutsidePixels(appUnitsPerDevPixel));
@@ -1583,7 +1619,7 @@ FrameLayerBuilder::BuildContainerLayerFor(nsDisplayListBuilder* aBuilder,
       // invalidated.
       state.SetInvalidateAllThebesContent();
     }
-    SetHasContainerLayer(aContainerFrame);
+    SetHasContainerLayer(aContainerFrame, currentOffset);
   }
 
   Clip clip;