Fix another caret paint invalidation issue

third_party/WebKit/Source/core/editing/CaretDisplayItemClient.cpp

 /*
  * Copyright (C) 2004, 2008, 2009, 2010 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 107 matching lines @@
 void CaretDisplayItemClient::updateStyleAndLayoutIfNeeded(
     const PositionWithAffinity& caretPosition) {
   // This method may be called multiple times (e.g. in partial lifecycle
   // updates) before a paint invalidation. We should save m_previousLayoutBlock
   // and m_visualRectInPreviousLayoutBlock only if they have not been saved
   // since the last paint invalidation to ensure the caret painted in the
   // previous paint invalidated block will be invalidated. We don't care about
   // intermediate changes of layoutBlock because they are not painted.
   if (!m_previousLayoutBlock) {
     m_previousLayoutBlock = m_layoutBlock;
+    DCHECK(m_visualRectInPreviousLayoutBlock.isEmpty());
     m_visualRectInPreviousLayoutBlock = m_visualRect;
   }
 
   LayoutBlock* newLayoutBlock = caretLayoutBlock(caretPosition.anchorNode());
   if (newLayoutBlock != m_layoutBlock) {
     if (m_layoutBlock)
       m_layoutBlock->setMayNeedPaintInvalidation();
     m_layoutBlock = newLayoutBlock;
     if (newLayoutBlock)
       m_needsPaintInvalidation = true;
@@ skipping 46 matching lines @@
                                                       context);
   if (!isImmediateFullPaintInvalidationReason(
           m_previousLayoutBlock->fullPaintInvalidationReason())) {
     objectInvalidator.invalidatePaintRectangleWithContext(
         m_visualRectInPreviousLayoutBlock, PaintInvalidationCaret);
   }
 
   context.paintingLayer->setNeedsRepaint();
   objectInvalidator.invalidateDisplayItemClient(*this, PaintInvalidationCaret);
   m_previousLayoutBlock = nullptr;
+  m_visualRectInPreviousLayoutBlock = LayoutRect();
 }
 
 void CaretDisplayItemClient::invalidatePaintInCurrentLayoutBlock(
     const PaintInvalidatorContext& context) {
   DCHECK(m_layoutBlock);
 
   LayoutRect newVisualRect;
   if (!m_localRect.isEmpty()) {
     newVisualRect = m_localRect;
     context.mapLocalRectToPaintInvalidationBacking(*m_layoutBlock,
                                                    newVisualRect);
     newVisualRect.move(m_layoutBlock->scrollAdjustmentForPaintInvalidation(
         *context.paintInvalidationContainer));
 
     if (m_layoutBlock->usesCompositedScrolling()) {
       // The caret should use scrolling coordinate space.
       DCHECK(m_layoutBlock == context.paintInvalidationContainer);
       newVisualRect.move(LayoutSize(m_layoutBlock->scrolledContentOffset()));
     }
   }
 
-  if (m_layoutBlock == m_previousLayoutBlock)
+  if (m_layoutBlock == m_previousLayoutBlock &&
+      m_visualRect == m_visualRectInPreviousLayoutBlock) {

[chrishtr, 2017/03/10 05:06:07]

Why is this conditional required? Can't figure this out yet. Add a comment also?

     m_previousLayoutBlock = nullptr;
+    m_visualRectInPreviousLayoutBlock = LayoutRect();
+  }
 
   ObjectPaintInvalidatorWithContext objectInvalidator(*m_layoutBlock, context);
   if (!m_needsPaintInvalidation && newVisualRect == m_visualRect) {
     // The caret may change paint offset without changing visual rect, and we
     // need to invalidate the display item client if the block is doing full
     // paint invalidation.
     if (isImmediateFullPaintInvalidationReason(
             m_layoutBlock->fullPaintInvalidationReason()) ||
         // For non-SPv2, ForcedSubtreeInvalidationChecking may hint change of
         // paint offset. See ObjectPaintInvalidatorWithContext::
@@ skipping 39 matching lines @@
 
 String CaretDisplayItemClient::debugName() const {
   return "Caret";
 }
 
 LayoutRect CaretDisplayItemClient::visualRect() const {
   return m_visualRect;
 }
 
 }  // namespace blink