Detect change on the intersection of video and viewport.

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

Index: third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
diff --git a/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp b/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
index a1f0ce6a74d593703d34135af4a59c9ecdc1652e..6ff870222d36a03427e6b1f491a99a49914337f8 100644
--- a/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
@@ -39,6 +39,7 @@
 #include "core/dom/ElementTraversal.h"
 #include "core/dom/ElementVisibilityObserver.h"
 #include "core/dom/Fullscreen.h"
+#include "core/dom/IntersectionGeometry.h"
 #include "core/dom/TaskRunnerHelper.h"
 #include "core/dom/shadow/ShadowRoot.h"
 #include "core/events/Event.h"
@@ -126,6 +127,10 @@ using DocumentElementSetMap =
 
 namespace {
 
+constexpr int64_t kOneHundredPercent = 100;
+constexpr int64_t kMostlyFillViewportThresholdPercent = 85;
+constexpr double kMostlyFillViewportBecomeStableTime = 5;

[ojan, 2016/11/24 00:48:33]

Nit: I generally prefer time values to say the unit of time to be extra clear.
So, I'd make this kMostlyFillViewportBecomeStableSeconds.

[xjz, 2016/11/24 02:16:16]

Done.

+
 enum MediaControlsShow {
   MediaControlsShowAttribute = 0,
   MediaControlsShowFullscreen,
@@ -410,6 +415,9 @@ HTMLMediaElement::HTMLMediaElement(const QualifiedName& tagName,
       m_playbackProgressTimer(this,
                               &HTMLMediaElement::playbackProgressTimerFired),
       m_audioTracksTimer(this, &HTMLMediaElement::audioTracksTimerFired),
+      m_viewportFillDebouncerTimer(
+          this,
+          &HTMLMediaElement::viewportFillDebouncerTimerFired),
       m_playedTimeRanges(),
       m_asyncEventQueue(GenericEventQueue::create(this)),
       m_playbackRate(1.0f),
@@ -1192,6 +1200,8 @@ void HTMLMediaElement::startPlayerLoad(const KURL& playerProvidedUrl) {
 
   m_webMediaPlayer->load(loadType(), source, corsMode());
 
+  m_webMediaPlayer->stablyFilledMostViewport(m_mostlyFillingViewport);
+
   if (isFullscreen()) {
     // This handles any transition to or from fullscreen overlay mode.
     frame->chromeClient().enterFullscreenForElement(this);
@@ -2504,6 +2514,8 @@ void HTMLMediaElement::startPlaybackProgressTimer() {
 }
 
 void HTMLMediaElement::playbackProgressTimerFired(TimerBase*) {
+  checkViewportIntersectionChanged();
+
   if (!std::isnan(m_fragmentEndTime) && currentTime() >= m_fragmentEndTime &&
       getDirectionOfPlayback() == Forward) {
     m_fragmentEndTime = std::numeric_limits<double>::quiet_NaN();
@@ -4193,4 +4205,42 @@ IntRect HTMLMediaElement::AutoplayHelperClientImpl::absoluteBoundingBoxRect()
   return result;
 }
 
+void HTMLMediaElement::checkViewportIntersectionChanged() {

[ojan, 2016/11/24 00:48:33]

Can we early return if we're not tab casting so we only need to do this work
when tab casting? The intersection work isn't *very* expensive, but it's not
cheap either.

Looks like we don't plumb that data in today, but I think it should be possible
to via RemoteRenderingController? In either case, putting a TODO and doing so a
followup patch would be fine.

[xjz, 2016/11/24 02:16:16]

Add TODO comment for now. Will see if this can be resolved in a follow-up CL.

+  ExecutionContext* context = getExecutionContext();
+  DCHECK(context->isDocument());
+  Document& document = toDocument(*context);
+  IntersectionGeometry geometry(&document, this, Vector<Length>(), true);

[ojan, 2016/11/24 00:48:33]

Now that you're in the HTMLElement world, you can get to the document more
directly with document(). 

https://cs.chromium.org/chromium/src/third_party/WebKit/Source/core/dom/Node....

Also, we generally try to avoid boolean arguments to functions unless it's
obvious what the bool is because it makes it hard to know what they are. From
the C++ style guide "Consider changing the function signature to replace a bool
argument with an enum argument. This will make the argument values
self-describing."

The typical solution here is to create an enum:
enum class IntersectionGeometryBounds {
  kShouldReportRootBounds,
  kShouldNotReportRootBounds,
}

[xjz, 2016/11/24 02:16:16]

Done. Name the enum as ReportRootBounds.

+  geometry.computeGeometry();
+  IntRect intersectRect = geometry.intersectionIntRect();
+  if (m_currentIntersectRect == intersectRect)
+    return;
+
+  m_currentIntersectRect = intersectRect;
+  // Reset on any intersection change, since this indicates the user is
+  // scrolling around in the document, the document is changing layout, etc.
+  m_viewportFillDebouncerTimer.stop();
+  bool isMostlyFillingViewport =
+      (kOneHundredPercent * m_currentIntersectRect.size().area() >
+       kMostlyFillViewportThresholdPercent *

[ojan, 2016/11/24 00:48:33]

Nit: If you make this kMostlyFillViewportThreshold and have the value be 0.85
instead of 85, then you can avoid needing the kOneHundredPercent value at all.

[xjz, 2016/11/24 02:16:16]

Done. 

+           geometry.rootIntRect().size().area());
+  if (m_mostlyFillingViewport == isMostlyFillingViewport)
+    return;
+
+  if (!isMostlyFillingViewport) {
+    m_mostlyFillingViewport = isMostlyFillingViewport;
+    if (m_webMediaPlayer)
+      m_webMediaPlayer->stablyFilledMostViewport(false);

[ojan, 2016/11/24 00:48:33]

Nit: It took me a bit to understand these few lines. Partially it's because you
use false here and isMostlyFillingViewport on line 4230. Either way is fine, but
it would make the code easier to read if you either use false in both places or
isMostlyFillingViewport in both places.

[xjz, 2016/11/24 02:16:16]

Done.

+    return;
+  }
+
+  m_viewportFillDebouncerTimer.startOneShot(kMostlyFillViewportBecomeStableTime,
+                                            BLINK_FROM_HERE);

[ojan, 2016/11/24 00:48:33]

Indentation is off here. FWIW, I haven't used it much, but a lot of people use
"git cl format" to have git cl fix these sorts of issues for them instead of
doing it manually.

[xjz, 2016/11/24 02:16:16]

I always do "git cl format". Is the "indentation" here not correct? Anyway,
after renaming |kMostlyFillViewportBecomeStableTime|, this is not applicable.

+}
+
+void HTMLMediaElement::viewportFillDebouncerTimerFired(TimerBase*) {
+  m_mostlyFillingViewport = true;
+  if (m_webMediaPlayer)
+    m_webMediaPlayer->stablyFilledMostViewport(true);
+}
+
 }  // namespace blink