Don't use cached subsequence when clip changes

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

Index: third_party/WebKit/Source/core/paint/PaintLayerClipper.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerClipper.cpp b/third_party/WebKit/Source/core/paint/PaintLayerClipper.cpp
index 7bb1bae8ee63a317d586216baf13caabb48db6be..cee76d3d1ef7e4805c86f411c69cb42c5462b925 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerClipper.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerClipper.cpp
@@ -154,6 +154,7 @@ ClipRects* PaintLayerClipper::getClipRects(const ClipRectsContext& context) cons
 void PaintLayerClipper::clearClipRectsIncludingDescendants()

[chrishtr, 2015/11/18 00:32:02]

It looks like PaintLayer::updateLayerPositionsAfterLayout() calls this
unconditionally?

[Xianzhu, 2015/11/18 22:38:14]

You are right.

The latest patch checks actual change of painting clip rects.

 {
     m_cache = nullptr;
+    m_layoutObject.layer()->setNeedsRepaint();
 
     for (PaintLayer* layer = m_layoutObject.layer()->firstChild(); layer; layer = layer->nextSibling()) {
         layer->clipper().clearClipRectsIncludingDescendants();
@@ -164,6 +165,7 @@ void PaintLayerClipper::clearClipRectsIncludingDescendants(ClipRectsCacheSlot ca
 {
     if (m_cache)
         m_cache->clear(cacheSlot);
+    m_layoutObject.layer()->setNeedsRepaint();
 
     for (PaintLayer* layer = m_layoutObject.layer()->firstChild(); layer; layer = layer->nextSibling()) {
         layer->clipper().clearClipRectsIncludingDescendants(cacheSlot);