third_party/WebKit/LayoutTests/intersection-observer/helper-functions.js

// Some of the js-test.js boilerplate will add stuff to the top of the document early
// enough to screw with frame offsets that are measured by the test.  Delay all that
// jazz until the actual test code is finished.
setPrintTestResultsLazily();
self.jsTestIsAsync = true;

function rectArea(rect) {
  return (rect.left - rect.right) * (rect.bottom - rect.top);
}

function rectToString(rect) {
  return "[" + rect.left + ", " + rect.right + ", " + rect.top + ", " + rect.bottom + "]";
}

function entryToString(entry) {
  var ratio = ((entry.intersectionRect.width * entry.intersectionRect.height) /
               (entry.boundingClientRect.width * entry.boundingClientRect.height));
  return (
      "boundingClientRect=" + rectToString(entry.boundingClientRect) + "\n" +
      "intersectionRect=" + rectToString(entry.intersectionRect) + "\n" +
      "visibleRatio=" + ratio + "\n" +
      "rootBounds=" + rectToString(entry.rootBounds) + "\n" +
      "target=" + entry.target + "\n" +
      "time=" + entry.time);
}

function intersectionRatio(entry) {
  var targetArea = rectArea(entry.boundingClientRect);
  if (!targetArea)
    return 0;
  return rectArea(entry.intersectionRect) / targetArea;
}