IntersectionObserver: compute correct intersection ratio for 0x0 elements

When a 0x0 element is in view, its intersection ratio is defined[1] to be 1. BUG=662826 [1] https://wicg.github.io/IntersectionObserver/#update-intersection-observations-algo Review-Url: https://codereview.chromium.org/2556243003 Cr-Commit-Position: refs/heads/master@{#437617}

IntersectionObserver: compute correct intersection ratio for 0x0 elements
When a 0x0 element is in view, its intersection ratio is defined[1] to be 1. BUG=662826 [1] https://wicg.github.io/IntersectionObserver/#update-intersection-observations-algo Review-Url: https://codereview.chromium.org/2556243003 Cr-Commit-Position: refs/heads/master@{#437617}
8296d3b0 · skyostil · Commit bot · 804d3453 · 8296d3b0 · 8296d3b0
Commit 8296d3b0 authored Dec 09, 2016 by skyostil Committed by Commit bot Dec 09, 2016
3 changed files
--- a/third_party/WebKit/LayoutTests/intersection-observer/zero-area-element-hidden.html
+++ b/third_party/WebKit/LayoutTests/intersection-observer/zero-area-element-hidden.html
+<!DOCTYPE html>
+<script src="../resources/intersection-observer-helper-functions.js"></script>
+<script src="../resources/testharness.js"></script>
+<script src="../resources/testharnessreport.js"></script>
+
+<title>Ensure that a hidden zero-area element is treated correctly</title>
+
+<div id='target' style='width: 0px; height: 0px; position: fixed; top: -1000px'</div>"
+
+<script>
+'use strict';
+
+async_test(t => {
+  let target = document.getElementById('target');
+  let entries = [];
+  new IntersectionObserver(changes => {
+    entries.push(...changes);
+  }).observe(target);
+  waitForNotification(t.step_func_done(() => {
+    // Since the element is initially assumed to be hidden, there are no entries.
+    assert_equals(entries.length, 0);
+  }));
+});
+</script>
--- a/third_party/WebKit/LayoutTests/intersection-observer/zero-area-element-visible.html
+++ b/third_party/WebKit/LayoutTests/intersection-observer/zero-area-element-visible.html
+<!DOCTYPE html>
+<script src="../resources/intersection-observer-helper-functions.js"></script>
+<script src="../resources/testharness.js"></script>
+<script src="../resources/testharnessreport.js"></script>
+
+<title>Ensure that a visible zero-area element is given the correct intersection ratio</title>
+
+<div id='target' style='width: 0px; height: 0px'</div>"
+
+<script>
+'use strict';
+
+async_test(t => {
+  let target = document.getElementById('target');
+  let entries = [];
+  new IntersectionObserver(changes => {
+    entries.push(...changes);
+  }).observe(target);
+  waitForNotification(t.step_func_done(() => {
+    assert_equals(entries.length, 1);
+    assert_equals(entries[0].intersectionRatio, 1);
+  }));
+});
+</script>
--- a/third_party/WebKit/Source/core/dom/IntersectionObservation.cpp
+++ b/third_party/WebKit/Source/core/dom/IntersectionObservation.cpp
@@ -50,19 +50,22 @@ void IntersectionObservation::computeIntersectionObservations(
  //       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()) {
-    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;
+  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;
  }
  if (m_lastThresholdIndex != newThresholdIndex) {
    IntRect snappedRootBounds = geometry.rootIntRect();