[SP] Don't invalidate the whole scrolled tree

Source/core/paint/DeprecatedPaintLayerPainter.cpp

Index: Source/core/paint/DeprecatedPaintLayerPainter.cpp
diff --git a/Source/core/paint/DeprecatedPaintLayerPainter.cpp b/Source/core/paint/DeprecatedPaintLayerPainter.cpp
index 8282e7f9ed085d28b4b990393e0c150715e9394d..6d83ec28b215a58631fcdd4d9bbd141aa1521867 100644
--- a/Source/core/paint/DeprecatedPaintLayerPainter.cpp
+++ b/Source/core/paint/DeprecatedPaintLayerPainter.cpp
@@ -423,6 +423,10 @@ void DeprecatedPaintLayerPainter::paintChildren(unsigned childrenToVisit, Graphi
     LayerListMutationDetector mutationChecker(m_paintLayer.stackingNode());
 #endif
 
+    IntSize scrollOffsetAccumulation = paintingInfo.scrollOffsetAccumulation;
+    if (m_paintLayer.layoutObject()->hasOverflowClip())
+        scrollOffsetAccumulation += m_paintLayer.layoutBox()->scrolledContentOffset();
+
     DeprecatedPaintLayerStackingNodeIterator iterator(*m_paintLayer.stackingNode(), childrenToVisit);
     while (DeprecatedPaintLayerStackingNode* child = iterator.next()) {
         DeprecatedPaintLayerPainter childPainter(*child->layer());
@@ -431,10 +435,18 @@ void DeprecatedPaintLayerPainter::paintChildren(unsigned childrenToVisit, Graphi
         if (!childPainter.shouldPaintLayerInSoftwareMode(paintingInfo, paintFlags))
             continue;
 
+        DeprecatedPaintLayerPaintingInfo childPaintingInfo = paintingInfo;
+        childPaintingInfo.scrollOffsetAccumulation = scrollOffsetAccumulation;
+        // Rare case: accumulate scroll offset of non-stacking-context ancestors up to m_paintLayer.
+        for (DeprecatedPaintLayer* parentLayer = child->layer()->parent(); parentLayer != &m_paintLayer; parentLayer = parentLayer->parent()) {
+            if (parentLayer->layoutObject()->hasOverflowClip())
+                childPaintingInfo.scrollOffsetAccumulation += parentLayer->layoutBox()->scrolledContentOffset();
+        }
+
         if (!child->layer()->isPaginated())
-            childPainter.paintLayer(context, paintingInfo, paintFlags);
+            childPainter.paintLayer(context, childPaintingInfo, paintFlags);
         else
-            childPainter.paintPaginatedChildLayer(context, paintingInfo, paintFlags);
+            childPainter.paintPaginatedChildLayer(context, childPaintingInfo, paintFlags);
     }
 }
 
@@ -633,16 +645,10 @@ void DeprecatedPaintLayerPainter::paintFragmentWithPhase(PaintPhase phase, const
     PaintInfo paintInfo(context, pixelSnappedIntRect(clipRect.rect()), phase, paintBehavior, paintingRootForLayoutObject, 0, paintingInfo.rootLayer->layoutObject());
     OwnPtr<ScrollRecorder> scrollRecorder;
     LayoutPoint paintOffset = toPoint(fragment.layerBounds.location() - m_paintLayer.layoutBoxLocation());
-    if (&m_paintLayer != paintingInfo.rootLayer && paintingInfo.rootLayer->layoutObject()->hasOverflowClip()) {
-        // As a sublayer of the root layer, m_paintLayer's painting is not controlled by the ScrollRecorder
-        // created by BlockPainter of the root layer, so we need to issue ScrollRecorder for them separately.
-        // FIXME: This doesn't apply in slimming paint phase 2.
-        IntSize scrollOffset = paintingInfo.rootLayer->layoutBox()->scrolledContentOffset();
-        if (paintingInfo.rootLayer->scrollsOverflow() || !scrollOffset.isZero()) {
-            paintOffset += scrollOffset;
-            paintInfo.rect.move(scrollOffset);
-            scrollRecorder = adoptPtr(new ScrollRecorder(*paintInfo.context, *m_paintLayer.layoutObject(), paintInfo.phase, scrollOffset));
-        }
+    if (!paintingInfo.scrollOffsetAccumulation.isZero()) {

[chrishtr, 2015/06/03 18:46:08]

Can you explain more why we need to do this accumulation?

Also, test?

[Xianzhu, 2015/06/03 19:06:59]

This is covered by existing tests. Previously the failures were hidden because
we invalidate the whole scrolled tree.

I should have kept the comments at line 637-639 of the old code, and modified it
into:
  // As a descendant of the root layer, m_paintLayer's painting is not
controlled by the ScrollRecorders
  // created by BlockPainter of the ancestor layers up to the root layer, so we
need to issue ScrollRecorder
  // for this layer seperately, with the scroll offset (accumulated from the
root layer to the parent of this
  // layer), to get the same result as ScrollRecorder in BlockPainter.

Will insert this comment below.

Previously (code at left) we compensate the scroll offset of the root painting
layer only, missing the intermediate scroll layers between the root layer and
this layer.

[Xianzhu, 2015/06/03 19:42:41]

Done.

+        paintOffset += paintingInfo.scrollOffsetAccumulation;
+        paintInfo.rect.move(paintingInfo.scrollOffsetAccumulation);
+        scrollRecorder = adoptPtr(new ScrollRecorder(*paintInfo.context, *m_paintLayer.layoutObject(), paintInfo.phase, paintingInfo.scrollOffsetAccumulation));
     }
     m_paintLayer.layoutObject()->paint(paintInfo, paintOffset);
 }