Adapt and reland old position sticky implementation

third_party/WebKit/Source/core/layout/compositing/CompositingInputsUpdater.cpp

Index: third_party/WebKit/Source/core/layout/compositing/CompositingInputsUpdater.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/CompositingInputsUpdater.cpp b/third_party/WebKit/Source/core/layout/compositing/CompositingInputsUpdater.cpp
index 5fe741f854763cfcd01ec40b6d637b6c10f2e528..7c6a656c6fe4720daee84732aab641ebb046af06 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositingInputsUpdater.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositingInputsUpdater.cpp
@@ -4,7 +4,9 @@
 
 #include "core/layout/compositing/CompositingInputsUpdater.h"
 
+#include "core/frame/FrameView.h"
 #include "core/layout/LayoutBlock.h"
+#include "core/layout/LayoutView.h"
 #include "core/layout/compositing/CompositedLayerMapping.h"
 #include "core/layout/compositing/PaintLayerCompositor.h"
 #include "core/paint/PaintLayer.h"
@@ -25,7 +27,7 @@ CompositingInputsUpdater::~CompositingInputsUpdater()
 void CompositingInputsUpdater::update()
 {
     TRACE_EVENT0("blink", "CompositingInputsUpdater::update");
-    updateRecursive(m_rootLayer, DoNotForceUpdate, AncestorInfo());
+    updateRecursive(m_rootLayer, DoNotForceUpdate, AncestorInfo(m_rootLayer));
 }
 
 static const PaintLayer* findParentLayerOnClippingContainerChain(const PaintLayer* layer)
@@ -97,6 +99,25 @@ void CompositingInputsUpdater::updateRecursive(PaintLayer* layer, UpdateType upd
     if (!layer->childNeedsCompositingInputsUpdate() && updateType != ForceUpdate)
         return;
 
+    const PaintLayer* previousOverflowLayer = layer->ancestorOverflowLayer();
+    layer->updateAncestorOverflowLayer(info.lastOverflowLayer);
+    if (layer->needsCompositingInputsUpdate() && layer->layoutObject()->style()->position() == StickyPosition) {
+        if (info.lastOverflowLayer != previousOverflowLayer) {
+            // Remove sticky constraints from old ancestor scroller if there was a change.
+            if (previousOverflowLayer)
+                previousOverflowLayer->scrollableArea()->stickyConstraintsMap().remove(layer);
+
+            if (info.lastOverflowLayer->isRootLayer())
+                layer->layoutObject()->view()->frameView()->addViewportConstrainedObject(layer->layoutObject());
+            else if (previousOverflowLayer && previousOverflowLayer->isRootLayer())
+                layer->layoutObject()->view()->frameView()->removeViewportConstrainedObject(layer->layoutObject());
+        }
+        layer->layoutObject()->updateStickyPositionConstraints(info.lastOverflowLayer);
+
+        // Layer position needs to be updated before mapping clippedAbsoluteBoundingBox.

[chrishtr, 2016/03/09 16:53:08]

Why is the layer position not already up-to-date at this point?

[flackr, 2016/03/14 19:04:26]

The overflow layer may have just changed - and the sticky position is dependent
on this.

[chrishtr, 2016/03/16 21:52:39]

But layer positions should be set before the compositing step of the lifecycle,
no?

[flackr, 2016/03/22 21:44:32]

Yes, but without correct ancestor information. We can't accurately set the layer
position for sticky elements until we have the correct ancestor overflow
scroller. Perhaps we should skip sticky offsets during
updateLayerPositionRecursive?

Alternately, it seems like compositing inputs and layer position updates would
have to become part of the same walk.

+        layer->updateLayerPosition();
+    }
+
     m_geometryMap.pushMappingsToAncestor(layer, layer->parent());
 
     if (layer->hasCompositedLayerMapping())
@@ -163,6 +184,9 @@ void CompositingInputsUpdater::updateRecursive(PaintLayer* layer, UpdateType upd
     if (layer->stackingNode()->isStackingContext())
         info.ancestorStackingContext = layer;
 
+    if (layer->layoutObject()->hasOverflowClip())
+        info.lastOverflowLayer = layer;
+
     if (layer->scrollsOverflow())
         info.lastScrollingAncestor = layer;