Fix invalidation under scroll, and cull rect testing, of flipped-block writing mode elements.

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/)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 1367 matching lines @@
     const LayoutBoxModelObject& paintInvalidationContainer = paintInvalidationState.paintInvalidationContainer();
     ASSERT(paintInvalidationContainer == containerForPaintInvalidation());
 
     const LayoutRect oldBounds = previousPaintInvalidationRect();
     const LayoutPoint oldLocation = RuntimeEnabledFeatures::slimmingPaintInvalidationEnabled() ? LayoutPoint() : previousPositionFromPaintInvalidationBacking();
     LayoutRect newBounds = paintInvalidationState.computePaintInvalidationRectInBacking();
     LayoutPoint newLocation = RuntimeEnabledFeatures::slimmingPaintInvalidationEnabled() ? LayoutPoint() : paintInvalidationState.computePositionFromPaintInvalidationBacking();
 
     // Composited scrolling should not be included in the bounds and position tracking, because the graphics layer backing the scroller
     // does not move on scroll.
+    // TODO(chrishtr): can we just avoid adding in the scroll in the first place in LayoutBox::mapScrollingContentsRectToBoxSpace?
     if (compositedScrollsWithRespectTo(paintInvalidationContainer)) {
         LayoutSize inverseOffset(toLayoutBox(&paintInvalidationContainer)->scrolledContentOffset());
+        // Flipped-blocks scrolling grows in the opposite direction.
+        if (UNLIKELY(hasFlippedBlocksWritingMode()))
+            inverseOffset.setWidth(-inverseOffset.width());
+
+        PaintLayerScrollableArea* scrollableArea = paintInvalidationContainer.getScrollableArea();
+        DCHECK(scrollableArea);
+
+        // Adjust for the scroll origin. Flipped-blocks writing mode scrolling starts at a different origin.
+        if (UNLIKELY(hasFlippedBlocksWritingMode()))
+            inverseOffset = inverseOffset + toLayoutSize(LayoutPoint(scrollableArea->scrollOrigin()));

[wkorman, 2016/07/14 23:48:52]

nit: could use += and rm the rhs inverseOffset

[chrishtr, 2016/07/14 23:51:10]

Done.

+
         newLocation.move(inverseOffset);
         newBounds.move(inverseOffset);
     }
 
     setPreviousPaintInvalidationRect(newBounds);
     if (!RuntimeEnabledFeatures::slimmingPaintInvalidationEnabled())
         setPreviousPositionFromPaintInvalidationBacking(newLocation);
 
     if (!shouldCheckForPaintInvalidationRegardlessOfPaintInvalidationState() && paintInvalidationState.forcedSubtreeInvalidationRectUpdateWithinContainerOnly()) {
         // We are done updating the paint invalidation rect. No other paint invalidation work to do for this object.
@@ skipping 2277 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