Bug 724189. Don't invalidate entire frame when the frame has shadows or effects and the post-transform overflow area changes. r=mats

layout/generic/nsFrame.cpp

@@ -6729,6 +6729,9 @@ nsIFrame::FinishAndStoreOverflow(nsOverflowAreas& aOverflowAreas,
     RemoveStateBits(NS_FRAME_HAS_CLIP);
   }
 
+  bool preTransformVisualOverflowChanged =
+    !GetVisualOverflowRectRelativeToSelf().IsEqualInterior(aOverflowAreas.VisualOverflow());
+
   /* If we're transformed, transform the overflow rect by the current transformation. */
   bool hasTransform = IsTransformed();
   if (hasTransform) {
@@ -6751,8 +6754,6 @@ nsIFrame::FinishAndStoreOverflow(nsOverflowAreas& aOverflowAreas,
     Properties().Delete(nsIFrame::PreTransformOverflowAreasProperty());
   }
 
-  bool visualOverflowChanged =
-    !GetVisualOverflowRect().IsEqualInterior(aOverflowAreas.VisualOverflow());
   bool anyOverflowChanged;
   if (aOverflowAreas != nsOverflowAreas(bounds, bounds)) {
     anyOverflowChanged = SetOverflowAreas(aOverflowAreas);
@@ -6760,7 +6761,7 @@ nsIFrame::FinishAndStoreOverflow(nsOverflowAreas& aOverflowAreas,
     anyOverflowChanged = ClearOverflowRects();
   }
 
-  if (visualOverflowChanged) {
+  if (preTransformVisualOverflowChanged) {
     if (hasOutlineOrEffects) {
       // When there's an outline or box-shadow or SVG effects,
       // changes to those styles might require repainting of the old and new
@@ -6782,26 +6783,27 @@ nsIFrame::FinishAndStoreOverflow(nsOverflowAreas& aOverflowAreas,
       // changed (in particular, if it grows), we have to repaint the
       // new area here.
       Invalidate(aOverflowAreas.VisualOverflow());
-    } else if (hasTransform) {
-      // When there's a transform, changes to that style might require
-      // repainting of the old and new overflow areas in the widget.
-      // Repainting of the frame itself will not be required if there's
-      // a retained layer, so we can call InvalidateLayer here
-      // which will avoid repainting ThebesLayers if possible.
-      // nsCSSFrameConstructor::DoApplyRenderingChangeToTree repaints
-      // the old overflow area in the widget in response to
-      // nsChangeHint_UpdateTransformLayer. But since the new overflow
-      // area is not known at that time, we have to handle it here.
-      // If the overflow area hasn't changed, then it doesn't matter that
-      // we didn't reach here since repainting the old overflow area was enough.
-      // If there is no transform now, then the container layer for
-      // the transform will go away and the frame contents will change
-      // ThebesLayers, forcing it to be invalidated, so it doesn't matter
-      // that we didn't reach here.
-      InvalidateLayer(aOverflowAreas.VisualOverflow(),
-                      nsDisplayItem::TYPE_TRANSFORM);
     }
   }
+  if (anyOverflowChanged && hasTransform) {
+    // When there's a transform, changes to that style might require
+    // repainting of the old and new overflow areas in the widget.
+    // Repainting of the frame itself will not be required if there's
+    // a retained layer, so we can call InvalidateLayer here
+    // which will avoid repainting ThebesLayers if possible.
+    // nsCSSFrameConstructor::DoApplyRenderingChangeToTree repaints
+    // the old overflow area in the widget in response to
+    // nsChangeHint_UpdateTransformLayer. But since the new overflow
+    // area is not known at that time, we have to handle it here.
+    // If the overflow area hasn't changed, then it doesn't matter that
+    // we didn't reach here since repainting the old overflow area was enough.
+    // If there is no transform now, then the container layer for
+    // the transform will go away and the frame contents will change
+    // ThebesLayers, forcing it to be invalidated, so it doesn't matter
+    // that we didn't reach here.
+    InvalidateLayer(aOverflowAreas.VisualOverflow(),
+                    nsDisplayItem::TYPE_TRANSFORM);
+  }
 
   return anyOverflowChanged;
 }