[SPv2] Track paint offset change

third_party/WebKit/Source/core/paint/PaintInvalidator.cpp

Index: third_party/WebKit/Source/core/paint/PaintInvalidator.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintInvalidator.cpp b/third_party/WebKit/Source/core/paint/PaintInvalidator.cpp
index ae82764dc2734a175579fa0bf7c61d7246ea600f..69f189183c06ee0e63150caf0a0848faa9c19837 100644
--- a/third_party/WebKit/Source/core/paint/PaintInvalidator.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintInvalidator.cpp
@@ -332,6 +332,8 @@ void PaintInvalidator::updateContext(const LayoutObject& object,
   context.oldLocation = objectPaintInvalidator.previousLocationInBacking();
   context.newVisualRect = computeVisualRectInBacking(object, context);
   context.newLocation = computeLocationInBacking(object, context);
+  context.oldPaintOffset = object.previousPaintOffset();
+  context.newPaintOffset = context.treeBuilderContext.current.paintOffset;
 
   IntSize adjustment = object.scrollAdjustmentForPaintInvalidation(
       *context.paintInvalidationContainer);
@@ -340,6 +342,7 @@ void PaintInvalidator::updateContext(const LayoutObject& object,
 
   object.getMutableForPainting().setPreviousVisualRect(context.newVisualRect);
   objectPaintInvalidator.setPreviousLocationInBacking(context.newLocation);
+  object.getMutableForPainting().setPreviousPaintOffset(context.newPaintOffset);
 }
 
 void PaintInvalidator::invalidatePaintIfNeeded(
@@ -430,16 +433,21 @@ void PaintInvalidator::invalidatePaintIfNeeded(
       break;
   }
 
-  if (context.oldLocation != context.newLocation)
+  if (context.oldLocation != context.newLocation ||
+      (RuntimeEnabledFeatures::slimmingPaintV2Enabled() &&
+       context.oldPaintOffset != context.newPaintOffset)) {
     context.forcedSubtreeInvalidationFlags |=
         PaintInvalidatorContext::ForcedSubtreeInvalidationChecking;
+  }
 
   // TODO(crbug.com/533277): This is a workaround for the bug. Remove when we

[pdr., 2016/11/10 07:35:32]

WDYT about adding a little more info to this comment to make the spv1 and spv2
differences easier to understand?
// This is a workaround for detecting paint offset changes in fixed position
// subtrees and isn't necessary with SPv2 paint offset tracking. See:
crbug.com/533277

[Xianzhu, 2016/11/10 17:41:10]

Done.

   // detect paint offset change.
-  if (reason != PaintInvalidationNone &&
-      hasPercentageTransform(object.styleRef()))
+  if (!RuntimeEnabledFeatures::slimmingPaintV2Enabled() &&

[chrishtr, 2016/11/10 18:42:00]

How was this fixed for SPv2?

[Xianzhu, 2016/11/10 22:51:50]

Good question. To answer your question, at first I thought this were incorrect
because we do need to traverse the subtree to check for changed paint offsets.
Then I debugged with the test case
paint/invalidation/percentage-transform-paint-offset.html, and found that the
logic is actually redundant, even for SPv1. Created
https://codereview.chromium.org/2493673005/ to remove the logic. Waiting for try
results. Rebased this CL onto it.

+      reason != PaintInvalidationNone &&
+      hasPercentageTransform(object.styleRef())) {
     context.forcedSubtreeInvalidationFlags |=
         PaintInvalidatorContext::ForcedSubtreeInvalidationChecking;
+  }
 
   // TODO(crbug.com/490725): This is a workaround for the bug, to force
   // descendant to update visual rects on clipping change.