Add root margin support for IntersectionObserver.

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

 // 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/IntersectionObserver.h"
 
 #include "bindings/core/v8/ExceptionState.h"
 #include "core/css/parser/CSSParserTokenRange.h"
 #include "core/css/parser/CSSTokenizer.h"
 #include "core/dom/ElementIntersectionObserverData.h"
 #include "core/dom/ExceptionCode.h"
 #include "core/dom/ExecutionContext.h"
 #include "core/dom/IntersectionObserverCallback.h"
 #include "core/dom/IntersectionObserverController.h"
 #include "core/dom/IntersectionObserverEntry.h"
 #include "core/dom/IntersectionObserverInit.h"
 #include "core/html/HTMLFrameOwnerElement.h"
 #include "core/layout/LayoutView.h"
 #include "platform/Timer.h"
 #include "wtf/MainThread.h"
 #include <algorithm>
 
 namespace blink {
 
+static void parseRootMargin(String rootMarginParameter, Vector<Length>& rootMargin, ExceptionState& exceptionState)

[ojan, 2016/01/12 01:08:49]

TODO: We need to make sure this exact algorithm is specced somewhere.

[szager1, 2016/01/12 19:24:43]

Added TODO.

+{
+    // The root margin argument accepts syntax similar to that for CSS margin:
+    //
+    // "1px" = top/right/bottom/left
+    // "1px 2px" = top/bottom left/right
+    // "1px 2px 3px" = top left/right bottom
+    // "1px 2px 3px 4px" = top left right bottom
+    //
+    // Any extra stuff after the first four tokens is ignored.
+    CSSTokenizer::Scope tokenizerScope(rootMarginParameter);
+    CSSParserTokenRange tokenRange = tokenizerScope.tokenRange();
+    while (rootMargin.size() < 5 && tokenRange.peek().type() != EOFToken && !exceptionState.hadException()) {
+        const CSSParserToken& token = tokenRange.consumeIncludingWhitespace();
+        switch (token.type()) {
+        case PercentageToken:
+            rootMargin.append(Length(token.numericValue(), Percent));
+            break;
+        case DimensionToken:
+            switch (token.unitType()) {
+            case CSSPrimitiveValue::UnitType::Pixels:
+                rootMargin.append(Length(static_cast<int>(floor(token.numericValue())), Fixed));
+                break;
+            case CSSPrimitiveValue::UnitType::Percentage:
+                rootMargin.append(Length(token.numericValue(), Percent));
+                break;
+            default:
+                exceptionState.throwTypeError("rootMargin must be specified in pixels or percent.");
+            }
+            break;
+        default:
+            exceptionState.throwTypeError("rootMargin must be specified in pixels or percent.");
+        }
+    }
+}
+
 static void parseThresholds(const DoubleOrDoubleArray& thresholdParameter, Vector<float>& thresholds, ExceptionState& exceptionState)
 {
     if (thresholdParameter.isDouble()) {
         thresholds.append(static_cast<float>(thresholdParameter.getAsDouble()));
     } else {
         for (auto thresholdValue : thresholdParameter.getAsDoubleArray())
             thresholds.append(static_cast<float>(thresholdValue));
     }
 
     for (auto thresholdValue : thresholds) {
@@ skipping 15 matching lines @@
         ASSERT(context->isDocument());
         Frame* mainFrame = toDocument(context)->frame()->tree().top();
         if (mainFrame && mainFrame->isLocalFrame())
             root = toLocalFrame(mainFrame)->document()->documentElement();
     }
     if (!root) {
         exceptionState.throwDOMException(HierarchyRequestError, "Unable to get root element in main frame to track.");
         return nullptr;
     }
 
+    Vector<Length> rootMargin;
+    if (observerInit.hasRootMargin())
+        parseRootMargin(observerInit.rootMargin(), rootMargin, exceptionState);
+    if (exceptionState.hadException())
+        return nullptr;
+
     Vector<float> thresholds;
     if (observerInit.hasThreshold())
         parseThresholds(observerInit.threshold(), thresholds, exceptionState);
     else
         thresholds.append(0);
     if (exceptionState.hadException())
         return nullptr;
 
-    return new IntersectionObserver(callback, *root, thresholds);
+    return new IntersectionObserver(callback, *root, rootMargin, thresholds);
 }
 
-IntersectionObserver::IntersectionObserver(IntersectionObserverCallback& callback, Element& root, const Vector<float>& thresholds)
+IntersectionObserver::IntersectionObserver(IntersectionObserverCallback& callback, Element& root, const Vector<Length>& rootMargin, const Vector<float>& thresholds)
     : m_callback(&callback)
     , m_root(root.ensureIntersectionObserverData().createWeakPtr(&root))
     , m_thresholds(thresholds)
 {
+    switch (rootMargin.size()) {
+    case 0:
+        break;
+    case 1:
+        m_topMargin = m_rightMargin = m_bottomMargin = m_leftMargin = rootMargin[0];
+        break;
+    case 2:
+        m_topMargin = m_bottomMargin = rootMargin[0];
+        m_rightMargin = m_leftMargin = rootMargin[1];
+        break;
+    case 3:
+        m_topMargin = rootMargin[0];
+        m_rightMargin = m_leftMargin = rootMargin[1];
+        m_bottomMargin = rootMargin[2];
+        break;
+    case 4:
+        m_topMargin = rootMargin[0];
+        m_rightMargin = rootMargin[1];
+        m_bottomMargin = rootMargin[2];
+        m_leftMargin = rootMargin[3];
+        break;
+    default:
+        ASSERT_NOT_REACHED();
+        break;
+    }
     root.document().ensureIntersectionObserverController().addTrackedObserver(*this);
 }
 
 LayoutObject* IntersectionObserver::rootLayoutObject()
 {
     Element* rootElement = root();
     if (rootElement == rootElement->document().documentElement())
         return rootElement->document().layoutView();
     return rootElement->layoutObject();
 }
@@ skipping 32 matching lines @@
     if (m_root.get() == target) {
         exceptionState.throwDOMException(HierarchyRequestError, "Cannot use the same element for root and target.");
         return;
     }
     if (!isDescendantOfRoot(target)) {
         exceptionState.throwDOMException(HierarchyRequestError, "Observed element must be a descendant of the observer's root element.");
         return;
     }
 
     bool shouldReportRootBounds = target->document().frame()->securityContext()->securityOrigin()->canAccess(root()->document().frame()->securityContext()->securityOrigin());
+    if (!shouldReportRootBounds && hasPercentMargin()) {
+        exceptionState.throwDOMException(HierarchyRequestError, "Cannot observe a cross-origin target because the observer has a root margin value specified as a percent.");

[ojan, 2016/01/12 01:08:49]

TODO: I wonder if we should have a TODO or something to add a URL to this
description that can point people at some documentation explaining this. Or
maybe we should just make sure the IO documentation covers this.

[szager1, 2016/01/12 19:24:43]

Added a TODO.

+        return;
+    }
 
     if (target->ensureIntersectionObserverData().getObservationFor(*this))
         return;
 
     IntersectionObservation* observation = new IntersectionObservation(*this, *target, shouldReportRootBounds);
     target->ensureIntersectionObserverData().addObservation(*observation);
     m_observations.add(observation);
 }
 
 void IntersectionObserver::unobserve(Element* target, ExceptionState&)
@@ skipping 37 matching lines @@
     entries.swap(m_entries);
     return entries;
 }
 
 void IntersectionObserver::enqueueIntersectionObserverEntry(IntersectionObserverEntry& entry)
 {
     m_entries.append(&entry);
     toDocument(m_callback->executionContext())->ensureIntersectionObserverController().scheduleIntersectionObserverForDelivery(*this);
 }
 
+static LayoutUnit computeMargin(const Length& length, LayoutUnit referenceLength)
+{
+    if (length.type() == Percent)
+        return LayoutUnit(static_cast<int>(referenceLength.toFloat() * length.percent() / 100.0));
+    return LayoutUnit(length.intValue());

[ojan, 2016/01/12 01:08:49]

ASSERT(length.type() == Fixed); ?

[szager1, 2016/01/12 19:24:43]

Done.

+}
+
+void IntersectionObserver::applyRootMargin(LayoutRect& rect) const
+{
+    LayoutUnit topMargin = computeMargin(m_topMargin, rect.height());
+    LayoutUnit rightMargin = computeMargin(m_rightMargin, rect.width());

[ojan, 2016/01/12 01:08:49]

TODO: We should make sure the spec is clear that the left/right margins resolve
with respect to the width and not the height (since with most css layouts they
resolve against the height).

[szager1, 2016/01/12 19:24:43]

Added TODO.

+    LayoutUnit bottomMargin = computeMargin(m_bottomMargin, rect.height());
+    LayoutUnit leftMargin = computeMargin(m_leftMargin, rect.width());
+
+    rect.setX(rect.x() - leftMargin);
+    rect.setWidth(rect.width() + leftMargin + rightMargin);
+    rect.setY(rect.y() - topMargin);
+    rect.setHeight(rect.height() + topMargin + bottomMargin);
+}
+
 unsigned IntersectionObserver::firstThresholdGreaterThan(float ratio) const
 {
     unsigned result = 0;
     while (result < m_thresholds.size() && m_thresholds[result] < ratio)
         ++result;
     return result;
 }
 
 void IntersectionObserver::deliver()
 {
     checkRootAndDetachIfNeeded();
 
     if (m_entries.isEmpty())
         return;
 
     HeapVector<Member<IntersectionObserverEntry>> entries;
     entries.swap(m_entries);
     m_callback->handleEvent(entries, *this);
 }
 
 void IntersectionObserver::setActive(bool active)
 {
     checkRootAndDetachIfNeeded();
     for (auto& observation : m_observations)
         observation->setActive(m_root && active && isDescendantOfRoot(observation->target()));
 }
 
+bool IntersectionObserver::hasPercentMargin() const
+{
+    return (m_topMargin.type() == Percent
+        || m_rightMargin.type() == Percent
+        || m_bottomMargin.type() == Percent
+        || m_leftMargin.type() == Percent);
+}
+
 void IntersectionObserver::checkRootAndDetachIfNeeded()
 {
 #if ENABLE(OILPAN)
     // TODO(szager): Pre-oilpan, ElementIntersectionObserverData::dispose() will take
     // care of this cleanup.  When oilpan ships, there will be a potential leak of the
     // callback's execution context when the root goes away.  For a detailed explanation:
     //
     //   https://goo.gl/PC2Baj
     //
     // When that happens, this method should catch most potential leaks, but a complete
     // solution will still be needed, along the lines described in the above link.
     if (m_root)
         return;
     disconnect();
 #endif
 }
 
 DEFINE_TRACE(IntersectionObserver)
 {
     visitor->trace(m_callback);
     visitor->trace(m_root);
     visitor->trace(m_observations);
     visitor->trace(m_entries);
 }
 
 } // namespace blink