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 "core/dom/IntersectionObservation.h"
+
+#include "core/dom/ElementRareData.h"
+#include "core/dom/IntersectionObserver.h"
+#include "core/frame/FrameView.h"
+#include "core/layout/LayoutBox.h"
+#include "core/layout/LayoutText.h"
+#include "core/layout/LayoutView.h"
+#include "core/paint/PaintLayer.h"
+
+namespace blink {
+
+IntersectionObservation::IntersectionObservation(IntersectionObserver& observer, Element& target, bool shouldReportRootBounds)
+    : m_observer(observer)
+    , m_target(target.ensureIntersectionObserverData().createWeakPtr(&target))
+    , m_active(true)
+    , m_shouldReportRootBounds(shouldReportRootBounds)
+    , m_lastThresholdIndex(0)
+{
+    target.ensureIntersectionObserverData().addObservation(*this);

[haraken, 2015/12/22 01:13:30]

The logic around here is messy...

- IntersectionObserver::m_observations.add is called by IntersectionObserver.
- IntersectionObserver::m_observations.remove is called by
IntersectionObservation::disconnect.
- ElementIntersectionObserverData::m_intersectionObservations.add is called by
IntersectionObservation's constructor.
- ElementIntersectionObserverData::m_intersectionObservations.remove is called
by IntersectionObservation::disconnect.

Can we refactor the code as follows?

- IntersectionObservation's constructor calls
ElementIntersectionObserverData::addObservation. It calls
IntersectionObserver::m_observations.add and
ElementIntersectionObserverData::m_intersectionObservations.add.
- IntersectionObservation::disconnect calls
ElementIntersectionObserverData::removeObservation. It calls
IntersectionObserver::m_observations.remove and
ElementIntersectionObserverData::m_intersectionObservations.remove.

[esprehn, 2015/12/22 07:50:32]

Yeah it's nice if the constructor has no side effects and instead the caller
does the hook up.

[szager1, 2015/12/22 07:53:41]

I think this would be much more confusing, because it obscures the fact that two
different instances of ElementIntersetionObserverData are touched: one for the
root, and another for the target.  Calling from the target
ElementIntersectionObserverData instance into the root
ElementIntersectionObserverData is subtle and confusing.

I'll think about other ways to refactor this for clarity.

[szager1, 2015/12/22 08:49:50]

Moved the addObservation() call into the caller.

+}
+
+void IntersectionObservation::initializeGeometry(IntersectionGeometry& geometry)
+{
+    LayoutObject* targetLayoutObject = m_target->layoutObject();
+    if (targetLayoutObject->isBoxModelObject())
+        geometry.targetRect = toLayoutBoxModelObject(targetLayoutObject)->visualOverflowRect();
+    else
+        geometry.targetRect = toLayoutText(targetLayoutObject)->visualOverflowRect();
+    geometry.intersectionRect = geometry.targetRect;
+}
+
+void IntersectionObservation::clipToRoot(LayoutRect& rect)
+{
+    // Map and clip rect into root element coordinates.
+    LayoutObject* rootLayoutObject = m_observer->rootLayoutObject();
+    LayoutObject* targetLayoutObject = m_target->layoutObject();
+    targetLayoutObject->mapToVisibleRectInContainerSpace(toLayoutBoxModelObject(rootLayoutObject), rect, nullptr);
+    if (rootLayoutObject->hasOverflowClip()) {
+        LayoutBox* rootLayoutBox = toLayoutBox(rootLayoutObject);
+        LayoutRect clipRect(LayoutPoint(), LayoutSize(rootLayoutBox->layer()->size()));
+        m_observer->applyRootMargin(clipRect);
+        rootLayoutBox->flipForWritingMode(rect);

[esprehn, 2015/12/22 07:50:32]

ugh, writing mode incantations all over. Do we have a test for this?

[szager1, 2015/12/22 08:49:49]

No, this was cargo culted from
LayoutBox::applyCachedClipAndScrollOffsetForPaintInvalidation.  Added a TODO to
write a test.

+        rect.intersect(clipRect);
+        rootLayoutBox->flipForWritingMode(rect);
+    }
+}
+
+void IntersectionObservation::clipToFrameView(IntersectionGeometry& geometry)
+{
+    Element* rootElement = m_observer->root();
+    LayoutObject* rootLayoutObject = m_observer->rootLayoutObject();
+    if (rootElement == rootElement->document().documentElement()) {
+        geometry.rootRect = LayoutRect(rootElement->document().view()->visibleContentRect());
+        m_observer->applyRootMargin(geometry.rootRect);
+        geometry.intersectionRect.intersect(geometry.rootRect);
+    } else {
+        if (rootLayoutObject->isBox())
+            geometry.rootRect = LayoutRect(toLayoutBox(rootLayoutObject)->absoluteContentBox());
+        else
+            geometry.rootRect = LayoutRect(rootLayoutObject->absoluteBoundingBoxRect());
+        m_observer->applyRootMargin(geometry.rootRect);
+    }
+
+    LayoutPoint scrollPosition(rootElement->document().view()->scrollPosition());
+    geometry.targetRect.moveBy(-scrollPosition);
+    geometry.intersectionRect.moveBy(-scrollPosition);
+    geometry.rootRect.moveBy(-scrollPosition);
+}
+
+static void mapRectToDocumentCoordinates(LayoutObject* layoutObject, LayoutRect& rect)

[esprehn, 2015/12/22 07:50:32]

reference for layoutObject

[szager1, 2015/12/22 08:49:50]

Done.

+{
+    rect = LayoutRect(layoutObject->localToAbsoluteQuad(FloatQuad(FloatRect(rect)), UseTransforms | ApplyContainerFlip | TraverseDocumentBoundaries).boundingBox());
+}
+
+bool IntersectionObservation::computeGeometry(IntersectionGeometry& geometry)
+{
+    LayoutObject* rootLayoutObject = m_observer->rootLayoutObject();
+    LayoutObject* targetLayoutObject = m_target->layoutObject();
+    if (!rootLayoutObject->isBoxModelObject())
+        return false;
+    if (!targetLayoutObject->isBoxModelObject() && !targetLayoutObject->isText())

[esprehn, 2015/12/22 07:50:32]

hmm, how can target be a Text? observe() on a Text should throw, can an Element
get a Text layouter? Maybe <br> ?

[szager1, 2015/12/22 08:49:49]

Yeah, I think <br> would do it.  And I think there was interest in extending the
spec to cover text nodes at some point.

+        return false;
+
+    // Initialize targetRect and intersectionRect to bounds of target, in target's coordinate space.
+    initializeGeometry(geometry);
+
+    // TODO(szager): Support intersection observations for zero-area targets.  For now, we just
+    // punt on the observation.
+    if (!geometry.targetRect.size().width() || !geometry.targetRect.size().height())
+        return false;
+
+    // Clip intersectionRect to the root, and map it to root coordinates.
+    clipToRoot(geometry.intersectionRect);
+
+    // Map targetRect into document coordinates.
+    mapRectToDocumentCoordinates(targetLayoutObject, geometry.targetRect);
+
+    // Map intersectionRect into document coordinates.
+    mapRectToDocumentCoordinates(rootLayoutObject, geometry.intersectionRect);
+
+    // Clip intersectionRect to FrameView visible area if necessary, and map all geometry to frame coordinates.
+    clipToFrameView(geometry);
+
+    if (geometry.intersectionRect.size().isZero())
+        geometry.intersectionRect = LayoutRect();
+    if (!m_shouldReportRootBounds)
+        geometry.rootRect = LayoutRect();
+
+    return true;
+}
+
+void IntersectionObservation::computeIntersectionObservations(double timestamp)
+{
+    Element* targetElement = target();
+    if (!targetElement || !isActive())
+        return;
+    LayoutObject* targetLayoutObject = targetElement->layoutObject();
+    // TODO(szager): Support SVG
+    if (!targetLayoutObject || (!targetLayoutObject->isBox() && !targetLayoutObject->isInline()))
+        return;
+
+    IntersectionGeometry geometry;
+    if (!computeGeometry(geometry))
+        return;
+
+    float intersectionArea = geometry.intersectionRect.size().width().toFloat() * geometry.intersectionRect.size().height().toFloat();
+    float targetArea = geometry.targetRect.size().width().toFloat() * geometry.targetRect.size().height().toFloat();
+    if (!targetArea)
+        return;
+    float newVisibleRatio = intersectionArea / targetArea;
+    unsigned newThresholdIndex = observer()->firstThresholdGreaterThan(newVisibleRatio);
+    if (m_lastThresholdIndex != newThresholdIndex) {
+        IntersectionObserverEntry* newEntry = new IntersectionObserverEntry(
+            timestamp / 1000.0,
+            pixelSnappedIntRect(geometry.targetRect),
+            pixelSnappedIntRect(geometry.rootRect),
+            pixelSnappedIntRect(geometry.intersectionRect),
+            targetElement);
+        observer()->enqueueIntersectionObserverEntry(*newEntry);
+    }
+    setLastThresholdIndex(newThresholdIndex);
+}
+
+void IntersectionObservation::disconnect()
+{
+    observer()->disconnect(*this);
+    if (m_target)
+        m_target->ensureIntersectionObserverData().removeObservation(*this->observer());

[haraken, 2015/12/22 01:13:30]

I think you should clear m_target here.

[szager1, 2015/12/22 07:53:41]

Can you explain why?  In oilpan world, IntersectionObservation and m_target will
create a reference cycle (since I have changed m_target to be a Member), so they
should get gc'ed together.  In pre-oilpan world, m_target is a weak reference,
so IntersectionObserver will not keep it alive.

+}
+
+DEFINE_TRACE(IntersectionObservation)
+{
+    visitor->trace(m_observer);
+    visitor->trace(m_target);
+}
+
+} // namespace blink {