Adapt and reland old position sticky implementation

Source/core/frame/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 1545 matching lines @@
     frame().loader().saveScrollState();
 }
 
 void FrameView::didScrollTimerFired(Timer<FrameView>*)
 {
     if (m_frame->document() && m_frame->document()->layoutView()) {
         ResourceLoadPriorityOptimizer::resourceLoadPriorityOptimizer()->updateAllImageResourcePriorities();
     }
 }
 
-void FrameView::updateLayersAndCompositingAfterScrollIfNeeded()
+void FrameView::updateLayersAndCompositingAfterScrollIfNeeded(const DoubleSize& scrollDelta)
 {
     // Nothing to do after scrolling if there are no fixed position elements.
     if (!hasViewportConstrainedObjects())
         return;
 
     RefPtrWillBeRawPtr<FrameView> protect(this);
 
+    // Update sticky positioned elements which scroll with the viewport.
+    for (const auto& viewportConstrainedObject : *m_viewportConstrainedObjects) {
+        LayoutObject* layoutObject = viewportConstrainedObject;
+        DeprecatedPaintLayer* layer = toLayoutBoxModelObject(layoutObject)->layer();
+        if (layoutObject->style()->position() == StickyPosition && layer->scrollsWithViewport())
+            layer->updateLayerPositionsAfterOverflowScroll(scrollDelta);

[flackr, 2015/09/15 21:13:11]

+skobes, does this seem like the right way / place to update the viewport
constrained sticky elements after a frame view scroll?

[skobes, 2015/09/16 00:07:57]

Possibly, but keep in mind that FrameView scrolls are going away.  With root
layer scrolling you will have to hook
DeprecatedPaintLayerScrollableArea::setScrollOffset.

Related: can sticky-positioned elements be sticky inside overflow scrollers?  Or
do they only stick to the viewport?

[chrishtr, 2015/09/17 01:18:56]

This method of implementation is not performant enough. Iterating over all of
the position objects will take a long time, and has been a performance
bottleneck in the past.
The nearest scrolling ancestor:
https://drafts.csswg.org/css-position/Overview.html#sticky-pos

[flackr, 2015/09/22 22:25:32]

Agreed, my intention is to only add those sticky objects whose nearest ancestor
scroller is the FrameView to the FrameView's viewport constrained objects.
Currently, this information is not available when the style changes but I
believe Ojan was okay with propagating nearest ancestor scroller down during the
style recalc. Do you think this needs to be resolved before landing anything?

+    }
+
     // If there fixed position elements, scrolling may cause compositing layers to change.
     // Update widget and layer positions after scrolling, but only if we're not inside of
     // layout.
     if (!m_nestedLayoutCount) {
         updateWidgetPositions();
         if (LayoutView* layoutView = this->layoutView())
             layoutView->layer()->setNeedsCompositingInputsUpdate();
     }
 }
 
@@ skipping 538 matching lines @@
         // Don't scroll the FrameView!
         ASSERT_NOT_REACHED();
     }
 
     m_scrollPosition = newPosition;
 
     if (!scrollbarsSuppressed())
         m_pendingScrollDelta += scrollDelta;
 
     clearScrollAnchor();
-    updateLayersAndCompositingAfterScrollIfNeeded();
+    updateLayersAndCompositingAfterScrollIfNeeded(scrollDelta);
     scrollPositionChanged();
     frame().loader().client()->didChangeScrollOffset();
 }
 
 void FrameView::invalidatePaintForTickmarks() const
 {
     if (Scrollbar* scrollbar = verticalScrollbar())
         scrollbar->invalidate();
 }
 
@@ skipping 1007 matching lines @@
     // If no scrollbars are present, the content may still be scrollable.
     if (!scrollbar) {
         IntSize scrollSize = m_contentsSize - visibleContentRect().size();
         scrollSize.clampNegativeToZero();
         return orientation == HorizontalScrollbar ? scrollSize.width() : scrollSize.height();
     }
 
     return scrollbar->totalSize() - scrollbar->visibleSize();
 }
 
-void FrameView::setScrollOffset(const IntPoint& offset, ScrollType)
+void FrameView::setScrollOffset(const IntPoint& offset, ScrollType type)
 {
-    scrollTo(clampScrollPosition(offset));
+    if (type != CompositorScroll) {
+        // Scrolling is triggered directly in response to scrollbar thumb movement,
+        // but should be processed after compositing update. http://crbug.com/420741
+        DisableCompositingQueryAsserts disabler;
+        scrollTo(clampScrollPosition(offset));
+    } else {
+        scrollTo(clampScrollPosition(offset));
+    }
 }
 
-void FrameView::setScrollOffset(const DoublePoint& offset, ScrollType)
+void FrameView::setScrollOffset(const DoublePoint& offset, ScrollType type)
 {
-    scrollTo(clampScrollPosition(offset));
+    if (type != CompositorScroll) {
+        // Scrolling is triggered directly in response to scrollbar thumb movement,
+        // but should be processed after compositing update. http://crbug.com/420741
+        DisableCompositingQueryAsserts disabler;
+        scrollTo(clampScrollPosition(offset));
+    } else {
+        scrollTo(clampScrollPosition(offset));
+    }
 }
 
 void FrameView::windowResizerRectChanged()
 {
     updateScrollbars(scrollOffsetDouble());
 }
 
 bool FrameView::hasOverlayScrollbars() const
 {
 
@@ skipping 756 matching lines @@
 
     if (!graphicsLayer)
         return;
 
     DeprecatedPaintLayer::mapRectToPaintInvalidationBacking(localFrame->contentLayoutObject(), paintInvalidationContainer, viewRect);
 
     graphicsLayerTimingRequests.add(graphicsLayer, Vector<std::pair<int64_t, WebRect>>()).storedValue->value.append(std::make_pair(m_frame->frameID(), enclosingIntRect(viewRect)));
 }
 
 } // namespace blink