Fix inline focus ring paint invalidation on continuation change

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

Index: third_party/WebKit/Source/core/layout/LayoutObject.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutObject.cpp b/third_party/WebKit/Source/core/layout/LayoutObject.cpp
index a09d8ad25d9c9d78267b03cd21a0d957732c71f1..f82bc7ba23000c87d41c12041598201115aef465 100644
--- a/third_party/WebKit/Source/core/layout/LayoutObject.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutObject.cpp
@@ -3423,11 +3423,27 @@ inline void LayoutObject::markAncestorsForPaintInvalidation() {
 inline void LayoutObject::setNeedsPaintOffsetAndVisualRectUpdate() {
   if (needsPaintOffsetAndVisualRectUpdate())
     return;
-  m_bitfields.setNeedsPaintOffsetAndVisualRectUpdate(true);
-  for (LayoutObject* parent = paintInvalidationParent();
-       parent && !parent->needsPaintOffsetAndVisualRectUpdate();
-       parent = parent->paintInvalidationParent())
-    parent->m_bitfields.setNeedsPaintOffsetAndVisualRectUpdate(true);
+  for (auto* object = this;
+       object && !object->needsPaintOffsetAndVisualRectUpdate();
+       object = object->paintInvalidationParent()) {
+    object->m_bitfields.setNeedsPaintOffsetAndVisualRectUpdate(true);
+
+    // Focus ring is special because continuations affect shape of focus ring.
+    // Mark the start object for paint invalidation if it has focus ring.

[wkorman, 2017/03/22 18:10:56]

My core question was actually, what ends up taking care of paint invalidation of
the rest of the continuation? I don't know much about continuations yet so am
interested to know for myself for future.

Or, put differently, what is special about the start, why do we not need similar
special code to mark mid- and end-continuations?

[Xianzhu, 2017/03/22 19:18:13]

<span style="outline: auto">
  ABC
  <div style="position: relative; width: 100px; height: 100px"></div>
  DEF
</span>

The layout tree is like:

      LayoutBlockFlow (anonymous) 0x11073c21c4d0
        LayoutInline 0x11073c22c010 continuation=0x11073c21c3a0	SPAN
style="outline: auto"
          LayoutText 0x11073c22c0d8    	#text "\n  ABC\n  "
      LayoutBlockFlow (anonymous) 0x11073c21c3a0 continuation=0x11073c22c1a0
        LayoutBlockFlow (relative positioned) 0x11073c21c270	DIV
style="position: relative; width: 100px; height: 100px"
      LayoutBlockFlow (anonymous) 0x11073c21c600
        LayoutInline 0x11073c22c1a0    	SPAN style="outline: auto"
          LayoutText 0x11073c22c268    	#text "\n  DEF\n"
        LayoutText 0x11073c22c330      	#text "\n"

The span is the start object of the continuation. It needs to paint a focus ring
enclosing the div (I guess the behavior is simply because of historical
reasons), though the div doesn't belong to the span in the layout tree. Focus
ring is the only case that paint invalidation of start of continuation depends
on continuations. For any other cases, paint invalidation just happens normally
in the above layout tree.

We have special condition to prevent the tail of the continuation
(0x11073c22c1a0 in the above tree) from painting the outline again.

[wkorman, 2017/03/22 20:28:53]

Ah, I see. Thank you for the explanation!

+    if (!object->isAnonymous() || !object->isLayoutBlockFlow())
+      continue;
+    auto* blockFlow = toLayoutBlockFlow(object);
+    if (!blockFlow->isAnonymousBlockContinuation())
+      continue;
+    if (auto* inlineElementContinuation =
+            blockFlow->inlineElementContinuation()) {
+      auto* startOfContinuations =
+          inlineElementContinuation->node()->layoutObject();
+      if (startOfContinuations &&
+          startOfContinuations->styleRef().outlineStyleIsAuto())
+        startOfContinuations->setMayNeedPaintInvalidation();
+    }
+  }
 }
 
 void LayoutObject::setShouldInvalidateSelection() {