Land layer squashing behind a flag

Source/core/rendering/RenderLayer.cpp

Index: Source/core/rendering/RenderLayer.cpp
diff --git a/Source/core/rendering/RenderLayer.cpp b/Source/core/rendering/RenderLayer.cpp
index 323d1957feaafe1d7f55fdb751baf80aa8b2de2a..0c5c7e54d8203362a95887acbaf5521e0e3f256d 100644
--- a/Source/core/rendering/RenderLayer.cpp
+++ b/Source/core/rendering/RenderLayer.cpp
@@ -134,6 +134,7 @@ RenderLayer::RenderLayer(RenderLayerModelObject* renderer)
     , m_staticInlinePosition(0)
     , m_staticBlockPosition(0)
     , m_enclosingPaginationLayer(0)
+    , m_groupedMapping(0)
     , m_repainter(renderer)
     , m_clipper(renderer)
 {
@@ -1110,15 +1111,16 @@ static inline const RenderLayer* compositingContainer(const RenderLayer* layer)
 
 // FIXME: having two different functions named enclosingCompositingLayer and enclosingCompositingLayerForRepaint
 // is error-prone and misleading for reading code that uses these functions - especially compounded with
-// the includeSelf option. It is very likely that some call sites of this function actually mean to use
-// enclosingCompositingLayerForRepaint().
+// the includeSelf option. It is very likely that we don't even want either of these functions; A layer
+// should be told explicitly which GraphicsLayer is the repaintContainer for a RenderLayer, and
+// any other use cases should probably have an API between the non-compositing and compositing sides of code.
 RenderLayer* RenderLayer::enclosingCompositingLayer(bool includeSelf) const
 {
-    if (includeSelf && hasCompositedLayerMapping())
+    if (includeSelf && compositingState() != NotComposited && compositingState() != PaintsIntoGroupedBacking)
         return const_cast<RenderLayer*>(this);
 
     for (const RenderLayer* curr = compositingContainer(this); curr; curr = compositingContainer(curr)) {
-        if (curr->hasCompositedLayerMapping())
+        if (curr->compositingState() != NotComposited && curr->compositingState() != PaintsIntoGroupedBacking)
             return const_cast<RenderLayer*>(curr);
     }
 
@@ -1127,11 +1129,11 @@ RenderLayer* RenderLayer::enclosingCompositingLayer(bool includeSelf) const
 
 RenderLayer* RenderLayer::enclosingCompositingLayerForRepaint(bool includeSelf) const
 {
-    if (includeSelf && compositingState() == PaintsIntoOwnBacking)
+    if (includeSelf && (compositingState() == PaintsIntoOwnBacking || compositingState() == PaintsIntoGroupedBacking))
         return const_cast<RenderLayer*>(this);
 
     for (const RenderLayer* curr = compositingContainer(this); curr; curr = compositingContainer(curr)) {
-        if (curr->compositingState() == PaintsIntoOwnBacking)
+        if (curr->compositingState() == PaintsIntoOwnBacking || curr->compositingState() == PaintsIntoGroupedBacking)
             return const_cast<RenderLayer*>(curr);
     }
 
@@ -1884,7 +1886,7 @@ static bool paintForFixedRootBackground(const RenderLayer* layer, PaintLayerFlag
 
 void RenderLayer::paintLayer(GraphicsContext* context, const LayerPaintingInfo& paintingInfo, PaintLayerFlags paintFlags)
 {
-    if (compositingState() != NotComposited) {
+    if (compositingState() != NotComposited && compositingState() != PaintsIntoGroupedBacking) {
         // The updatingControlTints() painting pass goes through compositing layers,
         // but we need to ensure that we don't cache clip rects computed with the wrong root in this case.
         if (context->updatingControlTints() || (paintingInfo.paintBehavior & PaintBehaviorFlattenCompositingLayers)) {
@@ -2225,6 +2227,11 @@ void RenderLayer::paintChildren(unsigned childrenToVisit, GraphicsContext* conte
     RenderLayerStackingNodeIterator iterator(*m_stackingNode, childrenToVisit);
     while (RenderLayerStackingNode* child = iterator.next()) {
         RenderLayer* childLayer = child->layer();
+
+        // Squashed RenderLayers should not paint into their ancestor.
+        if (childLayer->compositingState() == PaintsIntoGroupedBacking)
+            continue;
+
         if (!childLayer->isPaginated())
             childLayer->paintLayer(context, paintingInfo, paintFlags);
         else
@@ -3636,6 +3643,12 @@ CompositingState RenderLayer::compositingState() const
     // This is computed procedurally so there is no redundant state variable that
     // can get out of sync from the real actual compositing state.
 
+    if (m_groupedMapping) {
+        ASSERT(compositor()->isLayerSquashingEnabled());
+        ASSERT(!m_compositedLayerMapping);
+        return PaintsIntoGroupedBacking;
+    }
+
     if (!m_compositedLayerMapping)
         return NotComposited;
 
@@ -3997,10 +4010,17 @@ void RenderLayer::styleChanged(StyleDifference, const RenderStyle* oldStyle)
         || needsCompositingLayersRebuiltForClip(oldStyle, newStyle)
         || needsCompositingLayersRebuiltForOverflow(oldStyle, newStyle)
         || needsCompositingLayersRebuiltForFilters(oldStyle, newStyle, didPaintWithFilters)
-        || needsCompositingLayersRebuiltForBlending(oldStyle, newStyle))
+        || needsCompositingLayersRebuiltForBlending(oldStyle, newStyle)) {
         compositor()->setCompositingLayersNeedRebuild();
-    else if (hasCompositedLayerMapping())
+    } else if (compositingState() == PaintsIntoOwnBacking || compositingState() == HasOwnBackingButPaintsIntoAncestor) {
+        ASSERT(hasCompositedLayerMapping());
         compositedLayerMapping()->updateGraphicsLayerGeometry();
+    } else if (compositingState() == PaintsIntoGroupedBacking) {
+        ASSERT(compositor()->isLayerSquashingEnabled());
+        ASSERT(groupedMapping());
+        // FIXME: double-check that updateGraphicsLayerGeometry is not necessary (well the squashing portion is what might be needed? but probably not)...

[Ian Vollick, 2013/12/07 02:44:42]

I think we do want to update the geometry here. The position of the squashed
layer depends on the position of m_graphicsLayer and m_ancestorClippingLayer.
Those could updated due to this style change, couldn't they?

[shawnsingh, 2013/12/11 18:50:34]

(a) if the squashing layer is affected by m_graphicsLayer and
m_ancestorClippingLayer, they will be updated when updateGraphicsLayerGeometry()
is called by those layers.
(b) if the squashing layer is affected by layers of it's own, it won't affect
m_graphicsLayer and m_ancestorClippingLayer.

However, the idea that the squashingLayer itself may change it's own
size/position due to a style change.... means that we do probably need to
updateGraphicsLayerGeometry here.  New patch adds it, but keeps a variation of
the FIXME to follow-up later.

+        // FIXME: do we need to take any action here for a squashed layer?
+    }
 }
 
 bool RenderLayer::scrollsOverflow() const