IntersectionObserver: compute correct intersection ratio for 0x0 elements

third_party/WebKit/Source/core/dom/IntersectionObservation.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/IntersectionObservation.h"
 
 #include "core/dom/ElementRareData.h"
 #include "core/dom/IntersectionObserver.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
@@ skipping 193 matching lines @@
   //     - 0 means not intersecting.
   //     - 1 means intersecting.
   //     No other threshold crossings are possible.
   //   - Otherwise:
   //     - If root and target do not intersect, the threshold index is 0.
   //     - If root and target intersect but the intersection has zero-area
   //       (i.e., they have a coincident edge or corner), we consider the
   //       intersection to have "crossed" a zero threshold, but not crossed
   //       any non-zero threshold.
   unsigned newThresholdIndex;
-  float newVisibleRatio = 0;
-  if (geometry.targetRect.isEmpty()) {
-    newThresholdIndex = geometry.doesIntersect ? 1 : 0;
-  } else if (!geometry.doesIntersect) {
+  float newVisibleRatio;
+  if (geometry.doesIntersect) {
+    if (geometry.targetRect.isEmpty()) {
+      newVisibleRatio = 1;
+    } else {
+      float intersectionArea =
+          geometry.intersectionRect.size().width().toFloat() *
+          geometry.intersectionRect.size().height().toFloat();
+      float targetArea = geometry.targetRect.size().width().toFloat() *
+                         geometry.targetRect.size().height().toFloat();
+      newVisibleRatio = intersectionArea / targetArea;
+    }
+    newThresholdIndex = observer().firstThresholdGreaterThan(newVisibleRatio);
+  } else {
+    newVisibleRatio = 0;
     newThresholdIndex = 0;
-  } else {
-    float intersectionArea =
-        geometry.intersectionRect.size().width().toFloat() *
-        geometry.intersectionRect.size().height().toFloat();
-    float targetArea = geometry.targetRect.size().width().toFloat() *
-                       geometry.targetRect.size().height().toFloat();
-    newVisibleRatio = intersectionArea / targetArea;
-    newThresholdIndex = observer().firstThresholdGreaterThan(newVisibleRatio);
   }
   if (m_lastThresholdIndex != newThresholdIndex) {
     IntRect snappedRootBounds = pixelSnappedIntRect(geometry.rootRect);
     IntRect* rootBoundsPointer =
         m_shouldReportRootBounds ? &snappedRootBounds : nullptr;
     IntersectionObserverEntry* newEntry = new IntersectionObserverEntry(
         timestamp, newVisibleRatio, pixelSnappedIntRect(geometry.targetRect),
         rootBoundsPointer, pixelSnappedIntRect(geometry.intersectionRect),
         target());
     observer().enqueueIntersectionObserverEntry(*newEntry);
@@ skipping 12 matching lines @@
     target()->ensureIntersectionObserverData().removeObservation(observer());
   m_observer.clear();
 }
 
 DEFINE_TRACE(IntersectionObservation) {
   visitor->trace(m_observer);
   visitor->trace(m_target);
 }
 
 }  // namespace blink