Use intersection observer to control frame throttling

third_party/WebKit/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 16 matching lines @@
 #include "core/frame/FrameView.h"
 
 #include "core/HTMLNames.h"
 #include "core/MediaTypeNames.h"
 #include "core/animation/DocumentAnimations.h"
 #include "core/css/FontFaceSet.h"
 #include "core/css/resolver/StyleResolver.h"
 #include "core/dom/AXObjectCache.h"
 #include "core/dom/DOMNodeIds.h"
 #include "core/dom/Fullscreen.h"
+#include "core/dom/IntersectionObserverCallback.h"
 #include "core/dom/IntersectionObserverController.h"
+#include "core/dom/IntersectionObserverInit.h"
 #include "core/editing/EditingUtilities.h"
 #include "core/editing/FrameSelection.h"
 #include "core/editing/RenderedPosition.h"
 #include "core/editing/markers/DocumentMarkerController.h"
 #include "core/events/ErrorEvent.h"
 #include "core/fetch/ResourceFetcher.h"
 #include "core/frame/EventHandlerRegistry.h"
 #include "core/frame/FrameHost.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/Location.h"
@@ skipping 98 matching lines @@
 static bool s_initialTrackAllPaintInvalidations = false;
 
 FrameView::FrameView(LocalFrame* frame)
     : m_frame(frame),
       m_displayMode(WebDisplayModeBrowser),
       m_canHaveScrollbars(true),
       m_hasPendingLayout(false),
       m_inSynchronousPostLayout(false),
       m_postLayoutTasksTimer(this, &FrameView::postLayoutTimerFired),
       m_updateWidgetsTimer(this, &FrameView::updateWidgetsTimerFired),
-      m_renderThrottlingObserverNotificationFactory(
-          CancellableTaskFactory::create(
-              this,
-              &FrameView::notifyRenderThrottlingObservers)),
       m_isTransparent(false),
       m_baseBackgroundColor(Color::white),
       m_mediaType(MediaTypeNames::screen),
       m_safeToPropagateScrollToParent(true),
       m_scrollCorner(nullptr),
       m_stickyPositionObjectCount(0),
       m_inputEventsScaleFactorForEmulation(1),
       m_layoutSizeFixedToFrameSize(true),
       m_didScrollTimer(this, &FrameView::didScrollTimerFired),
       m_topControlsViewportAdjustment(0),
       m_needsUpdateWidgetGeometries(false),
       m_needsUpdateViewportIntersection(true),
-      m_needsUpdateViewportIntersectionInSubtree(true),
 #if ENABLE(ASSERT)
       m_hasBeenDisposed(false),
 #endif
       m_horizontalScrollbarMode(ScrollbarAuto),
       m_verticalScrollbarMode(ScrollbarAuto),
       m_horizontalScrollbarLock(false),
       m_verticalScrollbarLock(false),
       m_scrollbarsSuppressed(false),
       m_inUpdateScrollbars(false),
       m_frameTimingRequestsDirty(true),
-      m_viewportIntersectionValid(false),
       m_hiddenForThrottling(false),
-      m_crossOriginForThrottling(false),
       m_subtreeThrottled(false),
       m_currentUpdateLifecyclePhasesTargetState(
           DocumentLifecycle::Uninitialized),
       m_scrollAnchor(this),
       m_needsScrollbarsUpdate(false),
       m_suppressAdjustViewSize(false),
       m_allowsLayoutInvalidationAfterLayoutClean(true) {
   ASSERT(m_frame);
   init();
 }
@@ skipping 20 matching lines @@
 DEFINE_TRACE(FrameView) {
   visitor->trace(m_frame);
   visitor->trace(m_fragmentAnchor);
   visitor->trace(m_scrollableAreas);
   visitor->trace(m_animatingScrollableAreas);
   visitor->trace(m_autoSizeInfo);
   visitor->trace(m_horizontalScrollbar);
   visitor->trace(m_verticalScrollbar);
   visitor->trace(m_children);
   visitor->trace(m_viewportScrollableArea);
+  visitor->trace(m_intersectionObserver);
   visitor->trace(m_scrollAnchor);
   Widget::trace(visitor);
   ScrollableArea::trace(visitor);
 }
 
 void FrameView::reset() {
   m_hasPendingLayout = false;
   m_layoutSchedulingEnabled = true;
   m_inSynchronousPostLayout = false;
   m_layoutCount = 0;
@@ skipping 40 matching lines @@
   reset();
 
   m_size = LayoutSize();
 
   // Propagate the marginwidth/height and scrolling modes to the view.
   if (m_frame->owner() &&
       m_frame->owner()->scrollingMode() == ScrollbarAlwaysOff)
     setCanHaveScrollbars(false);
 }
 
+void FrameView::setupRenderThrottling() {
+  if (m_intersectionObserver || !frame().document() ||
+      !frame().document()->frame() || !frame().document()->documentElement() ||
+      !frame().document()->documentElement()->isConnected()) {
+    return;
+  }
+
+  ExecutionContext* context;
+  IntersectionObserverInit observerInit;
+  // Intersection observer does not currently support remote frames. As a
+  // workaround we monitor visibility up to the local root (crbug.com/615156).
+  Frame* mainFrame = frame().tree().top();
+  if (!mainFrame || !mainFrame->isLocalFrame()) {
+    observerInit.setRoot(
+        frame().localFrameRoot()->document()->documentElement());
+    context = &observerInit.root()->document();
+  } else {
+    context = toLocalFrame(mainFrame)->document();
+  }
+
+  IntersectionObserverCallback* callback =
+      new IntersectionObserverCallback(this, context);
+  m_intersectionObserver = IntersectionObserver::create(observerInit, *callback,
+                                                        ASSERT_NO_EXCEPTION);
+  m_intersectionObserver->observe(frame().document()->documentElement());
+
+  // Initially the intersection observer assumes the target is hidden. If it
+  // actually is, no notification about this will be delivered. To work around
+  // this, we set the observer into an undefined state so the first
+  // notification will always get delivered.
+  for (auto& observation : m_intersectionObserver->observations())
+    observation->setLastThresholdIndex(std::numeric_limits<unsigned>::max());

[ojan, 2016/10/14 02:25:47]

This is digging into the guts of IntersectionObserver algorithm too much.
Instead, we should probably add a first-class feature that lets you declare that
you want to assume targets are visible by default.

I don't know if that should be a value on the IntersectionObserver constructor
or on the observe call. I think for consistency with other configuration bits,
it should probably be on the constructor. I filed a bug at
https://github.com/WICG/IntersectionObserver/issues/163 to track changing the
web exposed API, but in the meantime, we can implement what we need and then
rejigger it to match the web exposed API once there's agreement on what that
should look like.

That sound OK?

[Sami, 2016/10/25 17:47:12]

Yeah, sounds good. I've added an explicit method for this now since I couldn't
figure out how to add something to IntersectionObserverInit without also
exposing it to the web.

+}
+
 void FrameView::dispose() {
   RELEASE_ASSERT(!isInPerformLayout());
 
   if (ScrollAnimatorBase* scrollAnimator = existingScrollAnimator())
     scrollAnimator->cancelAnimation();
   cancelProgrammaticScrollAnimation();
 
   detachScrollbars();
 
   if (ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator())
     scrollingCoordinator->willDestroyScrollableArea(this);
 
   // We need to clear the RootFrameViewport's animator since it gets called
   // from non-GC'd objects and RootFrameViewport will still have a pointer to
   // this class.
   if (m_viewportScrollableArea)
     m_viewportScrollableArea->clearScrollAnimators();
 
   clearScrollAnimators();
 
   // Destroy |m_autoSizeInfo| as early as possible, to avoid dereferencing
   // partially destroyed |this| via |m_autoSizeInfo->m_frameView|.
   m_autoSizeInfo.clear();
 
   m_postLayoutTasksTimer.stop();
   m_didScrollTimer.stop();
 
-  m_renderThrottlingObserverNotificationFactory->cancel();
-
   // FIXME: Do we need to do something here for OOPI?
   HTMLFrameOwnerElement* ownerElement = m_frame->deprecatedLocalOwner();
   // TODO(dcheng): It seems buggy that we can have an owner element that
   // points to another Widget.
   if (ownerElement && ownerElement->ownedWidget() == this)
     ownerElement->setWidget(nullptr);
 
 #if ENABLE(ASSERT)
   m_hasBeenDisposed = true;
 #endif
@@ skipping 3010 matching lines @@
 }
 
 void FrameView::setParent(Widget* parentView) {
   if (parentView == parent())
     return;
 
   Widget::setParent(parentView);
 
   updateScrollableAreaSet();
   setNeedsUpdateViewportIntersection();
+  setupRenderThrottling();
+
+  if (parentFrameView())
+    m_subtreeThrottled = parentFrameView()->canThrottleRendering();
 }
 
 void FrameView::removeChild(Widget* child) {
   ASSERT(child->parent() == this);
 
   if (child->isFrameView())
     removeScrollableArea(toFrameView(child));
 
   child->setParent(0);
   m_children.remove(child);
@@ skipping 936 matching lines @@
   if (layoutObject.isText())
     return;
 
   layoutObject.addAnnotatedRegions(regions);
   for (LayoutObject* curr = layoutObject.slowFirstChild(); curr;
        curr = curr->nextSibling())
     collectAnnotatedRegions(*curr, regions);
 }
 
 void FrameView::setNeedsUpdateViewportIntersection() {
-  m_needsUpdateViewportIntersection = true;
   for (FrameView* parent = parentFrameView(); parent;
        parent = parent->parentFrameView())
     parent->m_needsUpdateViewportIntersectionInSubtree = true;
 }
 
-void FrameView::updateViewportIntersectionIfNeeded() {
-  if (!m_needsUpdateViewportIntersection)
-    return;
-  m_needsUpdateViewportIntersection = false;
-  m_viewportIntersectionValid = true;
-  FrameView* parent = parentFrameView();
-  if (!parent) {
-    m_viewportIntersection = frameRect();
-    return;
-  }
-  ASSERT(!parent->m_needsUpdateViewportIntersection);
-
-  // If our parent is hidden, then we are too.
-  if (parent->m_viewportIntersection.isEmpty()) {
-    m_viewportIntersection = parent->m_viewportIntersection;
-    return;
-  }
-
-  // Transform our bounds into the root frame's content coordinate space,
-  // making sure we have valid layout data in our parent document. If our
-  // parent is throttled, we'll use possible stale layout information and
-  // rely on the fact that another lifecycle update will be scheduled once
-  // our parent becomes unthrottled.
-  ASSERT(parent->lifecycle().state() >= DocumentLifecycle::LayoutClean ||
-         parent->shouldThrottleRendering());
-  m_viewportIntersection = parent->contentsToRootFrame(frameRect());
-
-  // TODO(skyostil): Expand the viewport to make it less likely to see stale
-  // content while scrolling.
-  IntRect viewport = parent->m_viewportIntersection;
-  m_viewportIntersection.intersect(viewport);
-}
-
 void FrameView::updateViewportIntersectionsForSubtree(
     DocumentLifecycle::LifecycleState targetState) {
-  bool hadValidIntersection = m_viewportIntersectionValid;
-  bool hadEmptyIntersection = m_viewportIntersection.isEmpty();
-  updateViewportIntersectionIfNeeded();
-
   // Notify javascript IntersectionObservers
   if (targetState == DocumentLifecycle::PaintClean &&
       frame().document()->intersectionObserverController())
     frame()
         .document()
         ->intersectionObserverController()
         ->computeTrackedIntersectionObservations();
 
-  // Adjust render throttling for iframes based on visibility
-  bool shouldNotify = !hadValidIntersection ||
-                      hadEmptyIntersection != m_viewportIntersection.isEmpty();
-  if (shouldNotify &&
-      !m_renderThrottlingObserverNotificationFactory->isPending())
-    m_frame->frameScheduler()->unthrottledTaskRunner()->postTask(
-        BLINK_FROM_HERE,
-        m_renderThrottlingObserverNotificationFactory->cancelAndCreate());
-
   if (!m_needsUpdateViewportIntersectionInSubtree)
     return;
   m_needsUpdateViewportIntersectionInSubtree = false;
 
   for (Frame* child = m_frame->tree().firstChild(); child;
        child = child->tree().nextSibling()) {
     if (!child->isLocalFrame())
       continue;
     if (FrameView* view = toLocalFrame(child)->view())
       view->updateViewportIntersectionsForSubtree(targetState);
   }
 }
 
-void FrameView::updateThrottlingStatus() {
-  // Only offscreen frames can be throttled. Note that we disallow throttling
-  // of 0x0 frames because some sites use them to drive UI logic.
-  DCHECK(m_viewportIntersectionValid);
-  m_hiddenForThrottling =
-      m_viewportIntersection.isEmpty() && !frameRect().isEmpty();
-
-  // We only throttle the rendering pipeline in cross-origin frames. This is
-  // to avoid a situation where an ancestor frame directly depends on the
-  // pipeline timing of a descendant and breaks as a result of throttling.
-  // The rationale is that cross-origin frames must already communicate with
-  // asynchronous messages, so they should be able to tolerate some delay in
-  // receiving replies from a throttled peer.
-  //
-  // Check if we can access our parent's security origin.
-  m_crossOriginForThrottling = false;
-  // If any of our parents are throttled, we must be too.
-  m_subtreeThrottled = false;
-  const SecurityOrigin* origin = frame().securityContext()->getSecurityOrigin();
-  for (Frame* parentFrame = m_frame->tree().parent(); parentFrame;
-       parentFrame = parentFrame->tree().parent()) {
-    const SecurityOrigin* parentOrigin =
-        parentFrame->securityContext()->getSecurityOrigin();
-    if (!origin->canAccess(parentOrigin))
-      m_crossOriginForThrottling = true;
-    if (parentFrame->isLocalFrame() && toLocalFrame(parentFrame)->view() &&
-        toLocalFrame(parentFrame)->view()->canThrottleRendering())
-      m_subtreeThrottled = true;
-  }
-  m_frame->frameScheduler()->setFrameVisible(!m_hiddenForThrottling);
-  m_frame->frameScheduler()->setCrossOrigin(m_crossOriginForThrottling);
+void FrameView::updateRenderThrottlingStatusForTesting() {
+  m_intersectionObserver->deliver();
 }
 
-void FrameView::notifyRenderThrottlingObserversForTesting() {
-  DCHECK(m_renderThrottlingObserverNotificationFactory->isPending());
-  notifyRenderThrottlingObservers();
-}
-
-void FrameView::notifyRenderThrottlingObservers() {
-  TRACE_EVENT0("blink", "FrameView::notifyRenderThrottlingObservers");
+void FrameView::updateRenderThrottlingStatus(bool hidden,
+                                             bool subtreeThrottled) {
+  TRACE_EVENT0("blink", "FrameView::updateRenderThrottlingStatus");
   DCHECK(!isInPerformLayout());
-  DCHECK(frame().document());
-  DCHECK(!frame().document()->inStyleRecalc());
+  DCHECK(!m_frame->document() || !m_frame->document()->inStyleRecalc());
   bool wasThrottled = canThrottleRendering();
 
-  updateThrottlingStatus();
+  // Note that we disallow throttling of 0x0 frames because some sites use
+  // them to drive UI logic.
+  m_hiddenForThrottling = hidden && !frameRect().isEmpty();
+  m_subtreeThrottled = subtreeThrottled;
 
-  frame().document()->onVisibilityMaybeChanged(!m_hiddenForThrottling);
+  bool isThrottled = canThrottleRendering();
+  bool becameUnthrottled = wasThrottled && !isThrottled;
 
-  bool becameThrottled = !wasThrottled && canThrottleRendering();
-  bool becameUnthrottled = wasThrottled && !canThrottleRendering();
+  // If this FrameView became unthrottled or throttled, we must make sure all
+  // its children are notified synchronously. Otherwise we 1) might attempt to
+  // paint one of the children with an out-of-date layout before
+  // |updateRenderThrottlingStatus| has made it throttled or 2) fail to
+  // unthrottle a child whose parent is unthrottled by a later notification.
+  if (wasThrottled != isThrottled) {
+    for (const Member<Widget>& child : *children()) {
+      if (child->isFrameView()) {
+        FrameView* childView = toFrameView(child);
+        childView->updateRenderThrottlingStatus(
+            childView->m_hiddenForThrottling, isThrottled);
+      }
+    }
+  }
+
   ScrollingCoordinator* scrollingCoordinator = this->scrollingCoordinator();
-  if (becameThrottled) {
-    // If this FrameView became throttled, we must make sure all of its
-    // children become throttled at the same time. Otherwise we might
-    // attempt to paint one of the children with an out-of-date layout
-    // before |notifyRenderThrottlingObservers| has made it throttled.
-    forAllNonThrottledFrameViews([](FrameView& frameView) {
-      frameView.m_subtreeThrottled = true;
-      DCHECK(frameView.canThrottleRendering());
-    });
-  }
   if (becameUnthrottled) {
     // ScrollingCoordinator needs to update according to the new throttling
     // status.
     if (scrollingCoordinator)
       scrollingCoordinator->notifyGeometryChanged();
     // Start ticking animation frames again if necessary.
     if (page())
       page()->animator().scheduleVisualUpdate(m_frame.get());
     // Force a full repaint of this frame to ensure we are not left with a
     // partially painted version of this frame's contents if we skipped
@@ skipping 11 matching lines @@
     scrollingCoordinator->touchEventTargetRectsDidChange();
 
 #if DCHECK_IS_ON()
   // Make sure we never have an unthrottled frame inside a throttled one.
   FrameView* parent = parentFrameView();
   while (parent) {
     DCHECK(canThrottleRendering() || !parent->canThrottleRendering());
     parent = parent->parentFrameView();
   }
 #endif
+
+  if (frame().document()->frame())
+    frame().document()->onVisibilityMaybeChanged(!hidden);
 }
 
 bool FrameView::shouldThrottleRendering() const {
   return canThrottleRendering() && lifecycle().throttlingAllowed();
 }
 
 bool FrameView::canThrottleRendering() const {
   if (!RuntimeEnabledFeatures::renderingPipelineThrottlingEnabled())
     return false;
+  // We only throttle the rendering pipeline in cross-origin frames. This is
+  // to avoid a situation where an ancestor frame directly depends on the
+  // pipeline timing of a descendant and breaks as a result of throttling.
+  // The rationale is that cross-origin frames must already communicate with
+  // asynchronous messages, so they should be able to tolerate some delay in
+  // receiving replies from a throttled peer.
   return m_subtreeThrottled ||
-         (m_hiddenForThrottling && m_crossOriginForThrottling);
+         (m_hiddenForThrottling && m_frame->isCrossOriginSubframe());
+}
+
+FrameView::IntersectionObserverCallback::IntersectionObserverCallback(
+    FrameView* frameView,
+    ExecutionContext* context)
+    : m_frameView(frameView), m_context(context) {}
+
+void FrameView::IntersectionObserverCallback::handleEvent(
+    const HeapVector<Member<IntersectionObserverEntry>>& entries,
+    IntersectionObserver&) {
+  if (!m_frameView)
+    return;
+  bool wasHidden = m_frameView->m_hiddenForThrottling;
+  bool isHidden = wasHidden;
+  if (!entries.isEmpty())
+    isHidden = !entries.last()->intersectionRatio();
+  if (wasHidden != isHidden) {
+    m_frameView->updateRenderThrottlingStatus(isHidden,
+                                              m_frameView->m_subtreeThrottled);
+  }
+}
+
+ExecutionContext* FrameView::IntersectionObserverCallback::getExecutionContext()
+    const {
+  return m_context.get();
+}
+
+DEFINE_TRACE(FrameView::IntersectionObserverCallback) {
+  blink::IntersectionObserverCallback::trace(visitor);
+  visitor->trace(m_frameView);
+  visitor->trace(m_context);
 }
 
 }  // namespace blink