Fix under-invalidation on SVG shape/image resize in subpixels

third_party/WebKit/Source/core/layout/svg/LayoutSVGShape.cpp

 /*
  * Copyright (C) 2004, 2005, 2007 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2008 Rob Buis <buis@kde.org>
  * Copyright (C) 2005, 2007 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2009 Google, Inc.
  * Copyright (C) 2009 Dirk Schulze <krit@webkit.org>
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
  * Copyright (C) 2009 Jeff Schiller <codedread@gmail.com>
  * Copyright (C) 2011 Renata Hodovan <reni@webkit.org>
  * Copyright (C) 2011 University of Szeged
@@ skipping 164 matching lines @@
 void LayoutSVGShape::layout() {
   LayoutAnalyzer::Scope analyzer(*this);
 
   // Invalidate all resources of this client if our layout changed.
   if (everHadLayout() && selfNeedsLayout())
     SVGResourcesCache::clientLayoutChanged(this);
 
   bool updateParentBoundaries = false;
   // updateShapeFromElement() also updates the object & stroke bounds - which
   // feeds into the paint invalidation rect - so we need to call it for both
   // the shape-update and the bounds-update flag, since .

[pdr., 2016/10/31 20:49:05]

Not your fault (https://crrev.com/fe8421b9573ca696e596248811edf0a5d23fc191) but
can you fix this broken comment:
// the shape-update and the bounds-update flag.

(remove ", since ")

[Xianzhu, 2016/10/31 22:10:30]

The fix is in https://codereview.chromium.org/2465983002/ :)

   if (m_needsShapeUpdate || m_needsBoundariesUpdate) {
+    FloatRect oldStrokeBoundingBox = strokeBoundingBox();

[pdr., 2016/10/31 20:49:05]

Are you using the stroke bounding box because it includes the object bounding
box too?

If so, could you add that as a comment?
// We use the stroke bounding box because it includes both the stroke and the
object bounding box.

[Xianzhu, 2016/10/31 22:10:30]

Used strokeBoundingBox just because it is used for paint invalidation below.
This should be correct[1] but using objectBoundingBox is more intuitive. Changed
to objectBoundingBox.

[1] It's correct because a) it catches object bounding box change in most cases,
b) if object bounding box changes but other changes (e.g. stroke width change)
happen to make stroke bounding box not change, other changes will cause paint
invalidation.

     updateShapeFromElement();
+    if (oldStrokeBoundingBox != strokeBoundingBox())
+      setShouldDoFullPaintInvalidation();
     m_needsShapeUpdate = false;
 
     m_paintInvalidationBoundingBox = strokeBoundingBox();
     SVGLayoutSupport::intersectPaintInvalidationRectWithResources(
         this, m_paintInvalidationBoundingBox);
     m_needsBoundariesUpdate = false;
 
     updateParentBoundaries = true;
   }
 
@@ skipping 131 matching lines @@
   return lengthContext.valueForLength(style()->svgStyle().strokeWidth());
 }
 
 LayoutSVGShapeRareData& LayoutSVGShape::ensureRareData() const {
   if (!m_rareData)
     m_rareData = wrapUnique(new LayoutSVGShapeRareData());
   return *m_rareData.get();
 }
 
 }  // namespace blink