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..efacfc60689c597d98367ad783bed465bbeead12 100644
--- a/third_party/WebKit/Source/core/html/AutoplayExperimentHelper.cpp
+++ b/third_party/WebKit/Source/core/html/AutoplayExperimentHelper.cpp
@@ -6,6 +6,7 @@
 #include "core/html/AutoplayExperimentHelper.h"
 
 #include "core/dom/Document.h"
+#include "core/frame/FrameView.h"
 #include "core/frame/Settings.h"
 #include "core/html/HTMLMediaElement.h"
 #include "core/layout/LayoutBox.h"
@@ -21,15 +22,22 @@ namespace blink {
 
 using namespace HTMLNames;
 
+// Seconds to wait after a video has stopped moving before playing it.
+static const double kViewportTimerPollDelay = 0.5;
+
 AutoplayExperimentHelper::AutoplayExperimentHelper(HTMLMediaElement& element)
     : m_element(element)
-    , m_mode(AutoplayExperimentConfig::Mode::Off)
+    , m_mode(Mode::ExperimentOff)
     , 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());
+        m_mode = fromString(document().settings()->autoplayExperimentMode());
 
-        if (m_mode != AutoplayExperimentConfig::Mode::Off) {
+        if (m_mode != Mode::ExperimentOff) {
             WTF_LOG(Media, "HTMLMediaElement: autoplay experiment set to %d",
                 m_mode);
         }
@@ -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 +94,163 @@ 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(IfViewport)) {
+        if (!enabled(IfPageVisible))
+            return;
+    }
+
+    if (LayoutObject* layoutObject = m_element.layoutObject()) {
+        LayoutMedia* layoutMedia = toLayoutMedia(layoutObject);
+        layoutMedia->setRequestPositionUpdates(true);
+    }
+
+    // Set this unconditionally, in case we have no layout object yet.
+    m_registeredWithLayoutObject = true;
+}
+
+void AutoplayExperimentHelper::unregisterForPositionUpdatesIfNeeded()
+{
+    if (m_registeredWithLayoutObject) {
+        if (LayoutObject* obj = m_element.layoutObject()) {
+            LayoutMedia* layoutMedia = toLayoutMedia(obj);
+            layoutMedia->setRequestPositionUpdates(false);
+        }
+    }
+
+    // Clear this unconditionally so that we don't re-register if we didn't
+    // have a LayoutObject now, but get one later.
+    m_registeredWithLayoutObject = false;
+}
+
+void AutoplayExperimentHelper::positionChanged(const IntRect& visibleRect)
+{
+    // 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.
+
+    m_lastVisibleRect = visibleRect;
+
+    if (!m_element.layoutObject())
+        return;
+
+    IntRect currentLocation = m_element.layoutObject()->absoluteBoundingBoxRect();
+    bool inViewport = meetsVisibilityRequirements();
+
+    if (m_lastLocation != currentLocation) {
+        m_lastLocationUpdateTime = monotonicallyIncreasingTime();
+        m_lastLocation = currentLocation;
+    }
+
+    if (inViewport && !m_wasInViewport) {
+        // Only reset the timer when we transition from not visible to
+        // visible, because resetting the timer isn't cheap.
+        m_viewportTimer.startOneShot(kViewportTimerPollDelay, BLINK_FROM_HERE);
+    }
+    m_wasInViewport = inViewport;
+}
+
+void AutoplayExperimentHelper::updatePositionNotificationRegistration()
+{
+    if (m_registeredWithLayoutObject) {
+        LayoutMedia* layoutMedia = toLayoutMedia(m_element.layoutObject());
+        layoutMedia->setRequestPositionUpdates(true);
+    }
+}
+
+void AutoplayExperimentHelper::triggerAutoplayViewportCheckForTesting()
+{
+    FrameView* view = document().view();
+    if (view)
+        positionChanged(view->rootFrameToContents(view->computeVisibleArea()));
+
+    // 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() - kViewportTimerPollDelay - 1;
+    viewportTimerFired(nullptr);
+}
+
+void AutoplayExperimentHelper::viewportTimerFired(Timer<AutoplayExperimentHelper>*)
+{
+    double now = monotonicallyIncreasingTime();
+    double delta = now - m_lastLocationUpdateTime;
+    if (delta < kViewportTimerPollDelay) {
+        // 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(kViewportTimerPollDelay - delta, BLINK_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
+{
+    if (enabled(IfPageVisible)
+        && m_element.document().pageVisibilityState() != PageVisibilityStateVisible)
+        return false;
+
+    if (!enabled(IfViewport))
+        return true;
+
+    if (m_lastVisibleRect.isEmpty())
+        return false;
+
+    LayoutObject* layoutObject = m_element.layoutObject();
+    if (!layoutObject)
+        return false;
+
+    IntRect currentLocation = layoutObject->absoluteBoundingBoxRect();
+
+    // If element completely fills the screen, then truncate it to exactly
+    // match the screen.  Any element that is wider just has to cover.
+    if (currentLocation.x() <= m_lastVisibleRect.x()
+        && currentLocation.x() + currentLocation.width() >= m_lastVisibleRect.x() + m_lastVisibleRect.width()) {
+        currentLocation.setX(m_lastVisibleRect.x());
+        currentLocation.setWidth(m_lastVisibleRect.width());
+    }
+
+    if (currentLocation.y() <= m_lastVisibleRect.y()
+        && currentLocation.y() + currentLocation.height() >= m_lastVisibleRect.y() + m_lastVisibleRect.height()) {
+        currentLocation.setY(m_lastVisibleRect.y());
+        currentLocation.setHeight(m_lastVisibleRect.height());
+    }
+
+    return m_lastVisibleRect.contains(currentLocation);
+}
+
 bool AutoplayExperimentHelper::maybeStartPlaying()
 {
     // See if we're allowed to autoplay now.
-    if (!isEligible()) {
+    if (!isEligible() || !meetsVisibilityRequirements()) {
         return false;
     }
 
@@ -99,6 +265,9 @@ bool AutoplayExperimentHelper::maybeStartPlaying()
 
 bool AutoplayExperimentHelper::isEligible() const
 {
+    if (m_mode == Mode::ExperimentOff)
+        return false;
+
     // If no user gesture is required, then the experiment doesn't apply.
     // This is what prevents us from starting playback more than once.
     // Since this flag is never set to true once it's cleared, it will block
@@ -106,46 +275,38 @@ bool AutoplayExperimentHelper::isEligible() const
     if (!m_element.isUserGestureRequiredForPlay())
         return false;
 
-    if (m_mode == AutoplayExperimentConfig::Mode::Off)
-        return false;
-
     // Make sure that this is an element of the right type.
-    if (!enabled(AutoplayExperimentConfig::Mode::ForVideo)
+    if (!enabled(ForVideo)
         && isHTMLVideoElement(m_element))
         return false;
 
-    if (!enabled(AutoplayExperimentConfig::Mode::ForAudio)
+    if (!enabled(ForAudio)
         && isHTMLAudioElement(m_element))
         return false;
 
     // If nobody has requested playback, either by the autoplay attribute or
     // a play() call, then do nothing.
-    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())
+    if (!m_playPending && !m_element.shouldAutoplay())
         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)
+    if (enabled(IfMobile)
         && !document().viewportDescription().isLegacyViewportType())
         return false;
 
-    // If media is muted, then autoplay when it comes into view.
-    if (enabled(AutoplayExperimentConfig::Mode::IfMuted))
+    // If we require muted media and this is muted, then it is eligible.
+    if (enabled(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;
 }
 
 void AutoplayExperimentHelper::muteIfNeeded()
 {
-    if (enabled(AutoplayExperimentConfig::Mode::PlayMuted)) {
+    if (enabled(PlayMuted)) {
         ASSERT(!isEligible());
         // If we are actually changing the muted state, then this will call
         // mutedChanged().  If isEligible(), then mutedChanged() will try
@@ -162,6 +323,7 @@ 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 +339,25 @@ Document& AutoplayExperimentHelper::document() const
     return m_element.document();
 }
 
+AutoplayExperimentHelper::Mode AutoplayExperimentHelper::fromString(const String& mode)
+{
+    Mode value = ExperimentOff;
+    if (mode.contains("-forvideo"))
+        value |= ForVideo;
+    if (mode.contains("-foraudio"))
+        value |= ForAudio;
+    if (mode.contains("-ifpagevisible"))
+        value |= IfPageVisible;
+    if (mode.contains("-ifviewport"))
+        value |= IfViewport;
+    if (mode.contains("-ifmuted"))
+        value |= IfMuted;
+    if (mode.contains("-ifmobile"))
+        value |= IfMobile;
+    if (mode.contains("-playmuted"))
+        value |= PlayMuted;
+
+    return value;
+}
+
 }