IntersectionObserver: second cut.

third_party/WebKit/Source/core/dom/IntersectionObserverController.cpp

Index: third_party/WebKit/Source/core/dom/IntersectionObserverController.cpp
diff --git a/third_party/WebKit/Source/core/dom/IntersectionObserverController.cpp b/third_party/WebKit/Source/core/dom/IntersectionObserverController.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..b5d828231fbf1a3d044e08059b0cfab23869d274
--- /dev/null
+++ b/third_party/WebKit/Source/core/dom/IntersectionObserverController.cpp
@@ -0,0 +1,66 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "core/dom/IntersectionObserverController.h"
+
+#include "core/dom/Document.h"
+
+namespace blink {
+
+typedef HeapVector<Member<IntersectionObserver>> IntersectionObserverVector;
+
+IntersectionObserverController::IntersectionObserverController()
+    : m_timer(this, &IntersectionObserverController::deliverIntersectionObservations)
+{
+}
+
+IntersectionObserverController::~IntersectionObserverController() { }
+
+void IntersectionObserverController::scheduleIntersectionObserverForDelivery(IntersectionObserver& observer)
+{
+    // TODO(szager): use idle callback with a timeout
+    if (!m_timer.isActive())
+        m_timer.startOneShot(0, BLINK_FROM_HERE);
+    m_pendingIntersectionObservers.add(&observer);
+}
+
+void IntersectionObserverController::deliverIntersectionObservations(Timer<IntersectionObserverController>*)
+{
+    IntersectionObserverVector observers;
+    copyToVector(m_pendingIntersectionObservers, observers);
+    m_pendingIntersectionObservers.clear();
+    for (auto& observer : observers)
+        observer->deliver();
+}
+
+void IntersectionObserverController::computeTrackedIntersectionObservations()
+{
+    // TODO(szager): Need to define timestamp.
+    double timestamp = currentTime();
+    for (auto& observer : m_trackedIntersectionObservers)

[haraken, 2016/01/07 00:48:17]

Just to confirm: It is not possible that m_trackedIntersectionObservers is
mutated while calling computeIntersectionObservations, right? (i.e., you don't
need to copy the hash set to a vector before starting the iteration.)

[szager1, 2016/01/07 07:12:22]

That's correct.  Javascript cannot run during the iteration, and there's nothing
in computeIntersectionObservations() that could alter
m_trackedIntersectionObservers.

+        observer->computeIntersectionObservations(timestamp);
+}
+
+void IntersectionObserverController::addTrackedObserver(IntersectionObserver& observer)
+{
+    m_trackedIntersectionObservers.add(&observer);
+}
+
+void IntersectionObserverController::removeTrackedObserversForRoot(const Element& root)
+{
+    HeapVector<Member<IntersectionObserver>> toRemove;
+    for (auto& observer : m_trackedIntersectionObservers) {
+        if (observer->root() == &root)
+            toRemove.append(observer);
+    }
+    m_trackedIntersectionObservers.removeAll(toRemove);
+}
+
+DEFINE_TRACE(IntersectionObserverController)
+{
+    visitor->trace(m_trackedIntersectionObservers);
+    visitor->trace(m_pendingIntersectionObservers);
+}
+
+} // namespace blink