Invalidate previousLocationInBacking in LayoutObject::clearPreviousVisualRects()

third_party/WebKit/Source/core/layout/LayoutObject.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2011 Apple Inc.
  *               All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved.
  *               (http://www.torchmobile.com/)
@@ skipping 1241 matching lines @@
 
 void LayoutObject::adjustPreviousPaintInvalidationForScrollIfNeeded(
     const DoubleSize& scrollDelta) {
   if (containerForPaintInvalidation().usesCompositedScrolling())
     return;
   m_previousVisualRect.move(LayoutSize(scrollDelta));
 }
 
 void LayoutObject::clearPreviousVisualRects() {
   setPreviousVisualRect(LayoutRect());
+  // Also invalidate the previous location by setting it to a special value so
+  // that it won't match any meaningful location.
+  ObjectPaintInvalidator(*this).setPreviousLocationInBacking(
+      LayoutPoint(LayoutUnit::nearlyMin(), LayoutUnit::nearlyMin()));
   // After clearing ("invalidating" the visual rects, mark this object as

[chrishtr, 2016/11/29 00:57:59]

Noticed a typo here with mismatched parens. Might as well fix in this CL.

[Xianzhu, 2016/11/29 01:43:27]

Done.

   // needing to re-compute them.
   setShouldDoFullPaintInvalidation();

[chrishtr, 2016/11/29 00:57:59]

This call here on line 1268 should cause full paint invalidation to be computed
for the object, which will
re-create the paint invalidation rect. I added it in this CL, for a very
similar-sounding reason:

https://chromium.googlesource.com/chromium/src/+/2234389b8ef6a9204d9a37bb1781...

Why wouldn't the same process also lead to previousLocationInBacking being the
correct value after paint
invalidation of the same lifecycle update?

[Xianzhu, 2016/11/29 01:43:27]

We'll get the location recomputed, but may miss
setForceSubtreeInvalidationCheckingWithinContainer (
https://cs.chromium.org/chromium/src/third_party/WebKit/Source/core/layout/La...):

  if (previousLocation != paintInvalidator.previousLocationInBacking()) {
    newPaintInvalidationState
        .setForceSubtreeInvalidationCheckingWithinContainer();
  }

if the new location happens to be LayoutPoint().

 }
 
 LayoutRect LayoutObject::absoluteVisualRect() const {
   LayoutRect rect = localVisualRect();
   mapToVisualRectInAncestorSpace(view(), rect);
   return rect;
 }
 
 LayoutRect LayoutObject::localVisualRect() const {
   NOTREACHED();
@@ skipping 2223 matching lines @@
     const blink::LayoutObject* root = object1;
     while (root->parent())
       root = root->parent();
     root->showLayoutTreeAndMark(object1, "*", object2, "-", 0);
   } else {
     WTFLogAlways("%s", "Cannot showLayoutTree. Root is (nil)");
   }
 }
 
 #endif