IntersectionObserver: second cut.

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

+// Copyright 2015 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 "config.h"
+#include "core/dom/IntersectionObservation.h"
+
+#include "core/dom/IntersectionObserver.h"
+#include "core/layout/LayoutObject.h"
+
+namespace blink {
+
+IntersectionObservation::IntersectionObservation(IntersectionObserver& observer, Element* target)

[dcheng, 2015/12/10 00:37:09]

target can't be null here, so make it a reference to make that clear.

[szager1, 2015/12/10 22:38:54]

That will be in the next patch.

+    : m_observer(observer)
+    , m_target(target->createWeakPtr())
+    , m_lastVisibleRatio(0)
+{
+    setActive(true);
+    target->addIntersectionObservation(*this);
+}
+
+void IntersectionObservation::setActive(bool active)
+{
+    m_active = active;
+    if (active)
+        m_canReportRootBounds = m_target->document().frame()->securityContext()->securityOrigin()->canAccess(m_observer->root()->document().frame()->securityContext()->securityOrigin());
+}
+
+void IntersectionObservation::computeIntersectionObservations(int timestamp)
+{
+    // TODO: rootMargin is not yet supported; need to clarify how it interacts with
+    // ancestor clipping (https://github.com/slightlyoff/IntersectionObserver/issues/70)
+    Element* targetElement = target();
+    if (!targetElement || !isActive())

[dcheng, 2015/12/10 00:37:09]

I don't see how this observation is ever cleaned up in the 'element was removed
and gced' case. It seems like it depends on the actual IntersectionObserver to
be cleaned up.

[szager1, 2015/12/10 22:38:54]

The target element is the only thing that holds a hard reference to the
IntersectionObservation.  If the target element gets gc'ed, then the observation
will get gc'ed at the same time.

+        return;
+    Element* rootElement = observer()->root();
+    LayoutObject* targetLayoutObject = targetElement->layoutObject();
+    // TODO: Support SVG
+    if (!targetLayoutObject || (!targetLayoutObject->isBox() && !targetLayoutObject->isInline()))
+        return;
+
+    LayoutRect targetRect, rootRect, intersectionRect;
+    if (!targetElement->computeIntersection(rootElement, targetRect, rootRect, intersectionRect))
+        return;
+    if (!m_canReportRootBounds)
+        rootRect = LayoutRect();
+
+    float intersectionArea = intersectionRect.size().width().toFloat() * intersectionRect.size().height().toFloat();
+    float targetArea = targetRect.size().width().toFloat() * targetRect.size().height().toFloat();
+    if (!targetArea)
+        return;
+    float newVisibleRatio = intersectionArea / targetArea;
+    size_t newThresholdIndex = observer()->firstThresholdGreaterThan(newVisibleRatio);
+    size_t oldThresholdIndex = observer()->firstThresholdGreaterThan(lastVisibleRatio());
+    setLastVisibleRatio(newVisibleRatio);
+    if (oldThresholdIndex != newThresholdIndex)
+        observer()->enqueueIntersectionObserverEntry(new IntersectionObserverEntry(timestamp / 1000., pixelSnappedIntRect(targetRect), pixelSnappedIntRect(rootRect), pixelSnappedIntRect(intersectionRect), targetElement));
+}
+
+void IntersectionObservation::disconnect()
+{
+    observer()->disconnect(*this);
+    if (m_target)
+        m_target->removeIntersectionObservation(*this);
+}
+
+DEFINE_TRACE(IntersectionObservation)
+{
+    visitor->trace(m_observer);
+    visitor->trace(m_target);
+}
+
+} // namespace blink {