Fix caret paint invalidation issues

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

Index: third_party/WebKit/Source/core/editing/CaretDisplayItemClient.cpp
diff --git a/third_party/WebKit/Source/core/editing/CaretDisplayItemClient.cpp b/third_party/WebKit/Source/core/editing/CaretDisplayItemClient.cpp
index b5089bc6d6662368fbf3e7f2ab0dee5810393380..902f77b4112fb211a1fe912ef4068eb659fed405 100644
--- a/third_party/WebKit/Source/core/editing/CaretDisplayItemClient.cpp
+++ b/third_party/WebKit/Source/core/editing/CaretDisplayItemClient.cpp
@@ -117,8 +117,12 @@ LayoutRect CaretDisplayItemClient::computeCaretRect(
 
 void CaretDisplayItemClient::updateStyleAndLayoutIfNeeded(
     const PositionWithAffinity& caretPosition) {
-  m_previousLayoutBlock = m_layoutBlock;
-  m_previousVisualRect = m_visualRect;
+  // We should save m_previousLayoutBlock and m_visualRectInPreviousLayoutBlock
+  // only if they have not been saved since the last paint invalidation.

[chrishtr, 2017/03/08 17:36:06]

This conditional is needed because there may be multiple layouts between
paint invalidations, right? If so, worth commenting to that effect.

And it seems this is unique to carets because they can be reparented without
an eager invalidation?

[Xianzhu, 2017/03/08 19:38:22]

Yes. Added comment.
Yes. Carets are also unique because they are managed by frames, but the
containing blocks invalidate and paint them.

+  if (!m_previousLayoutBlock) {
+    m_previousLayoutBlock = m_layoutBlock;
+    m_visualRectInPreviousLayoutBlock = m_visualRect;
+  }
 
   LayoutBlock* newLayoutBlock = caretLayoutBlock(caretPosition.anchorNode());
   if (newLayoutBlock != m_layoutBlock) {
@@ -182,7 +186,7 @@ void CaretDisplayItemClient::invalidatePaintInPreviousLayoutBlock(
   if (!isImmediateFullPaintInvalidationReason(
           layoutBlockPaintInvalidationReason)) {
     objectInvalidator.invalidatePaintRectangleWithContext(
-        m_previousVisualRect, PaintInvalidationCaret);
+        m_visualRectInPreviousLayoutBlock, PaintInvalidationCaret);
   }
 
   context.paintingLayer->setNeedsRepaint();
@@ -210,12 +214,23 @@ void CaretDisplayItemClient::invalidatePaintInCurrentLayoutBlock(
     }
   }
 
-  if (!m_needsPaintInvalidation && newVisualRect == m_visualRect)
+  if (m_layoutBlock == m_previousLayoutBlock)
+    m_previousLayoutBlock = nullptr;
+
+  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 (isImmediateFullPaintInvalidationReason(
+            layoutBlockPaintInvalidationReason)) {
+      objectInvalidator.invalidateDisplayItemClient(*this,
+                                                    PaintInvalidationCaret);
+    }
     return;
+  }
 
   m_needsPaintInvalidation = false;
 
-  ObjectPaintInvalidatorWithContext objectInvalidator(*m_layoutBlock, context);
   if (!isImmediateFullPaintInvalidationReason(
           layoutBlockPaintInvalidationReason)) {
     objectInvalidator.fullyInvalidatePaint(PaintInvalidationCaret, m_visualRect,