Include viewport visibility checks for autoplay experiment.

third_party/WebKit/Source/core/html/AutoplayExperimentHelper.cpp

Index: third_party/WebKit/Source/core/html/AutoplayExperimentHelper.cpp
diff --git a/third_party/WebKit/Source/core/html/AutoplayExperimentHelper.cpp b/third_party/WebKit/Source/core/html/AutoplayExperimentHelper.cpp
index 3aa5811dc2c6c232404f8dea9fbf040b989ce8f1..9a0b6d8ffbbf3b519cdc527f097d91b3afda9c37 100644
--- a/third_party/WebKit/Source/core/html/AutoplayExperimentHelper.cpp
+++ b/third_party/WebKit/Source/core/html/AutoplayExperimentHelper.cpp
@@ -21,10 +21,18 @@ namespace blink {
 
 using namespace HTMLNames;
 
+// How long do we wait after a scroll event before deciding that no more
+// scroll events are going to arrive?
+static const double viewportTimerPollDelay = 0.5;
+
 AutoplayExperimentHelper::AutoplayExperimentHelper(HTMLMediaElement& element)
     : m_element(element)
     , m_mode(AutoplayExperimentConfig::Mode::Off)
     , m_playPending(false)
+    , m_registeredWithLayoutObject(false)
+    , m_wasInViewport(false)
+    , m_lastLocationUpdateTime(-std::numeric_limits<double>::infinity())
+    , m_viewportTimer(this, &AutoplayExperimentHelper::viewportTimerFired)
 {
     if (document().settings()) {
         m_mode = AutoplayExperimentConfig::fromString(document().settings()->autoplayExperimentMode());
@@ -38,14 +46,19 @@ AutoplayExperimentHelper::AutoplayExperimentHelper(HTMLMediaElement& element)
 
 AutoplayExperimentHelper::~AutoplayExperimentHelper()
 {
+    unregisterForPositionUpdatesIfNeeded();
 }
 
 void AutoplayExperimentHelper::becameReadyToPlay()
 {
     // Assuming that we're eligible to override the user gesture requirement,
-    // then play.
+    // either play if we meet the visibility checks, or install a listener
+    // to wait for them to pass.
     if (isEligible()) {
-        prepareToPlay(GesturelessPlaybackStartedByAutoplayFlagImmediately);
+        if (meetsVisibilityRequirements())
+            prepareToPlay(GesturelessPlaybackStartedByAutoplayFlagImmediately);
+        else
+            registerForPositionUpdatesIfNeeded();
     }
 }
 
@@ -61,11 +74,19 @@ void AutoplayExperimentHelper::playMethodCalled()
         if (isEligible()) {
             // Remember that userGestureRequiredForPlay is required for
             // us to be eligible for the experiment.
-            // We are able to override the gesture requirement now, so
-            // do so.
-            prepareToPlay(GesturelessPlaybackStartedByPlayMethodImmediately);
+            // If we are able to override the gesture requirement now, then
+            // do so.  Otherwise, install an event listener if we need one.
+            if (meetsVisibilityRequirements()) {
+                // Override the gesture and play.
+                prepareToPlay(GesturelessPlaybackStartedByPlayMethodImmediately);
+            } else {
+                // Wait for viewport visibility.
+                registerForPositionUpdatesIfNeeded();
+            }
         }
 
+    } else if (m_element.isUserGestureRequiredForPlay()) {
+        unregisterForPositionUpdatesIfNeeded();
     }
 }
 
@@ -73,18 +94,143 @@ void AutoplayExperimentHelper::pauseMethodCalled()
 {
     // Don't try to autoplay, if we would have.
     m_playPending = false;
+    unregisterForPositionUpdatesIfNeeded();
 }
 
 void AutoplayExperimentHelper::mutedChanged()
 {
-    // In other words, start playing if we just needed 'mute' to autoplay.
+    // If we are no longer eligible for the autoplay experiment, then also
+    // quit listening for events.  If we are eligible, and if we should be
+    // playing, then start playing.  In other words, start playing if
+    // we just needed 'mute' to autoplay.
+    if (!isEligible()) {
+        unregisterForPositionUpdatesIfNeeded();
+    } else {
+        // Try to play.  If we can't, then install a listener.
+        if (!maybeStartPlaying())
+            registerForPositionUpdatesIfNeeded();
+    }
+}
+
+void AutoplayExperimentHelper::registerForPositionUpdatesIfNeeded()
+{
+    // If we don't require that the player is in the viewport, then we don't
+    // need the listener.
+    if (!enabled(AutoplayExperimentConfig::Mode::IfViewport)
+        && !enabled(AutoplayExperimentConfig::Mode::IfPageVisible))
+        return;
+
+    LayoutObject* layoutObject = m_element.layoutObject();
+    if (layoutObject && layoutObject->isMedia()) {
+        LayoutMedia* layoutMedia = static_cast<LayoutMedia*>(layoutObject);
+        layoutMedia->setRequestPositionUpdates(true);
+        m_registeredWithLayoutObject = true;
+    }
+}
+
+void AutoplayExperimentHelper::unregisterForPositionUpdatesIfNeeded()
+{
+    if (m_registeredWithLayoutObject) {
+        LayoutObject* obj = m_element.layoutObject();
+        if (obj && obj->isMedia()) {
+            LayoutMedia* layoutMedia = static_cast<LayoutMedia*>(obj);
+            layoutMedia->setRequestPositionUpdates(false);
+            m_registeredWithLayoutObject = false;
+        }
+    }
+}
+
+void AutoplayExperimentHelper::positionChanged()
+{
+    // Something, maybe position, has changed.  If applicable, start a
+    // timer to look for the end of a scroll operation.
+    // Don't do much work here.
+    // Also note that we are called quite often, including when the
+    // page becomes visible.  That's why we don't bother to register
+    // for page visibility changes explicitly.
+
+    LocationState curLocation(m_element);
+    const bool inViewport = meetsVisibilityRequirements(curLocation);
+
+    // If the location has changed, then record the time of the last change.
+    if (m_lastLocation != curLocation) {
+        m_lastLocationUpdateTime = monotonicallyIncreasingTime();
+        m_lastLocation = curLocation;
+    }
+
+    // If we have transitioned to be visible, then start the timer.
+    if (inViewport && !m_wasInViewport) {
+        // We have transitioned from not visible to visible.  Reset the timer
+        // to check if we should start autoplay.  We do this to avoid
+        // resetting the timer too often in this callback.
+        m_viewportTimer.startOneShot(viewportTimerPollDelay, FROM_HERE);
+    }
+    m_wasInViewport = inViewport;
+}
+
+void AutoplayExperimentHelper::triggerAutoplayViewportCheck()
+{
+    // This method is for testing.
+
+    // If we're registered to receive updates on position, pretend that we did
+    // receive one.
+    if (m_registeredWithLayoutObject) {
+        positionChanged();
+    }
+
+    // Make sure that the last update appears to be sufficiently far in the
+    // past to appear that scrolling has stopped by now in viewportTimerFired.
+    m_lastLocationUpdateTime = monotonicallyIncreasingTime() - viewportTimerPollDelay - 1;
+    viewportTimerFired(nullptr);
+}
+
+void AutoplayExperimentHelper::viewportTimerFired(Timer<AutoplayExperimentHelper>*)
+{
+    double now = monotonicallyIncreasingTime();
+    double delta = now - m_lastLocationUpdateTime;
+    if (delta < viewportTimerPollDelay) {
+        // If we are not visible, then skip the timer.  It will be started
+        // again if we become visible again.
+        if (m_wasInViewport)
+            m_viewportTimer.startOneShot(viewportTimerPollDelay - delta, FROM_HERE);
+
+        return;
+    }
+
+    // Sufficient time has passed since the last scroll that we'll
+    // treat it as the end of scroll.  Autoplay if we should.
     maybeStartPlaying();
 }
 
+bool AutoplayExperimentHelper::meetsVisibilityRequirements(const LocationState& location) const
+{
+    if (enabled(AutoplayExperimentConfig::Mode::IfPageVisible)
+        && !location.isPageVisible())
+        return false;
+
+    return !enabled(AutoplayExperimentConfig::Mode::IfViewport)
+        || location.isElementVisible();
+}
+
+bool AutoplayExperimentHelper::meetsVisibilityRequirements() const
+{
+    // We could check for eligibility here, but we skip it.  Some of our
+    // callers need to do it separately, and we don't want to check more
+    // than we need to.
+
+    // If visibility isn't required, then it's visible enough.
+    if (!enabled(AutoplayExperimentConfig::Mode::IfViewport)
+        && !enabled(AutoplayExperimentConfig::Mode::IfPageVisible))
+        return true;
+
+    LocationState location(m_element);
+    return meetsVisibilityRequirements(location);
+}
+
 bool AutoplayExperimentHelper::maybeStartPlaying()
 {
     // See if we're allowed to autoplay now.
-    if (!isEligible()) {
+    if (!isEligible() || !meetsVisibilityRequirements()) {
         return false;
     }
 
@@ -123,23 +269,17 @@ bool AutoplayExperimentHelper::isEligible() const
     if (!m_playPending && !m_element.shouldAutoplay())
         return false;
 
-    // If the video is already playing, then do nothing.  Note that there
-    // is not a path where a user gesture is required but the video is
-    // playing.  However, we check for completeness.
-    if (!m_element.paused())
-        return false;
-
     // Note that the viewport test always returns false on desktop, which is
     // why video-autoplay-experiment.html doesn't check -ifmobile .
     if (enabled(AutoplayExperimentConfig::Mode::IfMobile)
         && !document().viewportDescription().isLegacyViewportType())
         return false;
 
-    // If media is muted, then autoplay when it comes into view.
+    // If we require muted media and this is muted, then it is eligible.
     if (enabled(AutoplayExperimentConfig::Mode::IfMuted))
         return m_element.muted();
 
-    // Autoplay when it comes into view (if needed), maybe muted.
+    // Element is eligible for gesture override, maybe muted.
     return true;
 }
 
@@ -162,6 +302,7 @@ void AutoplayExperimentHelper::prepareToPlay(AutoplayMetrics metric)
     // once.  Be sure to do this before muteIfNeeded().
     m_element.removeUserGestureRequirement();
 
+    unregisterForPositionUpdatesIfNeeded();
     muteIfNeeded();
 
     // Record that this autoplayed without a user gesture.  This is normally
@@ -177,4 +318,91 @@ Document& AutoplayExperimentHelper::document() const
     return m_element.document();
 }
 
+AutoplayExperimentHelper::LocationState::LocationState(Element& element)
+{
+    // Default to empty rectangles.  The screen is offset so that contains()
+    // returns false.
+    m_element = IntRect();
+    m_screen = IntRect(-1, -1, 0, 0);
+    ASSERT(!m_screen.contains(m_element));
+    m_visibilityState = PageVisibilityStateHidden;
+
+    const LocalDOMWindow* domWindow = element.document().domWindow();
+    if (!domWindow)
+        return;
+
+    // Get the page visibility.
+    Frame* frame = domWindow->frame();
+    if (!frame)
+        return;
+
+    Page* page = frame->page();
+    if (!page)
+        return;
+
+    m_visibilityState = page->visibilityState();
+
+    if (!element.layoutObject())
+        return;
+
+    const LayoutBox* elementBox = element.layoutObject()->enclosingBox();
+    if (!elementBox)
+        return;
+
+    float zoom = elementBox->style()->effectiveZoom();
+    m_element = IntRect(elementBox->offsetLeft().toInt()
+        , elementBox->offsetTop().toInt()
+        , elementBox->clientWidth().toInt()
+        , elementBox->clientHeight().toInt());
+
+    m_screen = IntRect(domWindow->scrollX()*zoom
+        , domWindow->scrollY()*zoom
+        , domWindow->innerWidth()*zoom
+        , domWindow->innerHeight()*zoom);
+}
+
+bool AutoplayExperimentHelper::LocationState::isElementVisible() const
+{
+    // Check if we're in the viewport.  If the element is bigger than the
+    // viewport, then be happy if it covers it.
+
+    IntRect element = m_element;
+    // If element completely fills the screen, then truncate it to exactly
+    // match the screen.  Any element that is wider just has to cover.
+    if (element.x() <= m_screen.x()
+        && element.x() + element.width() >= m_screen.x() + m_screen.width()) {
+        element.setX(m_screen.x());
+        element.setWidth(m_screen.width());
+    }
+
+    if (element.y() <= m_screen.y()
+        && element.y() + element.height() >= m_screen.y() + m_screen.height()) {
+        element.setY(m_screen.y());
+        element.setHeight(m_screen.height());
+    }
+
+    return m_screen.contains(element);
+}
+
+bool AutoplayExperimentHelper::LocationState::isPageVisible() const
+{
+    return m_visibilityState == PageVisibilityStateVisible;
+}
+
+bool AutoplayExperimentHelper::LocationState::operator==(const LocationState& them) const
+{
+    // As a special case, if either is missing position information, then
+    // they are not equal.
+    return !m_element.isEmpty() && !them.element().isEmpty()
+        && !m_screen.isEmpty() && !them.screen().isEmpty()
+        && m_visibilityState == them.visibilityState()
+        && m_screen == them.screen()
+        && m_element == them.element();
+}
+
+bool AutoplayExperimentHelper::LocationState::operator!=(const LocationState& them) const
+{
+    return !(*this == them);
+}
+
 }