Invalidate paint properties on paint offset changes

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc.
  *               All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 1674 matching lines @@
 
 void LayoutBox::frameRectChanged() {
   if (node() && node()->isElementNode()) {
     Element& element = toElement(*node());
     element.setNeedsResizeObserverUpdate();
   }
   // The frame rect may change because of layout of other objects.
   // Should check this object for paint invalidation.
   if (!needsLayout())
     setMayNeedPaintInvalidation();
+
+  if (RuntimeEnabledFeatures::slimmingPaintInvalidationEnabled()) {
+    // The overflow clip paint property depends on the frame rect
+    // (see: PaintPropertyTreeBuilder::updateOverflowClip).
+    if (hasOverflowClip() || styleRef().containsPaint() || hasControlClip())
+      setNeedsPaintPropertyUpdate();

[trchen, 2016/12/02 22:32:40]

This feel weird to me. The frameRect.location() should be included in the paint
offset and automatically caught already. frameRect.size() is the size of the
border box, but overflow clip uses the padding box. Do we also unconditionally
invalidate paint properties if border width changes?

[pdr., 2016/12/05 04:31:05]

+1, good catch.

This is hard to fix because we don't currently track whether the overflow clip
rect changes in the general case. I've updated this patch to invalidate
properties if a style change occurs on an overflowclip object with any border
values at all. I don't have data to prove it, but I think this is a reasonable
tradeoff because it's rare to have overflowclip + border + style change.

I added a bunch of tests in OverflowClipRecomputedOnChange.

+  }
 }
 
 bool LayoutBox::intersectsVisibleViewport() const {
   LayoutRect rect = visualOverflowRect();
   LayoutView* layoutView = view();
   while (!layoutView->frame()->ownerLayoutItem().isNull())
     layoutView =
         LayoutAPIShim::layoutObjectFrom(layoutView->frame()->ownerLayoutItem())
             ->view();
   mapToVisualRectInAncestorSpace(layoutView, rect);
@@ skipping 3918 matching lines @@
   LayoutRect rect = frameRect();
 
   LayoutBlock* block = containingBlock();
   if (block)
     block->adjustChildDebugRect(rect);
 
   return rect;
 }
 
 }  // namespace blink