<!DOCTYPE html>
<style>
body {
  display: flex;
  flex-wrap: wrap;
}
div {
  position: relative;
  padding: 2px;
  border: 1px solid black;
  min-width: 10px;
  min-height: 10px;
}
</style>

<body></body>

<script src='../resources/runner.js'></script>
<script src='../resources/generate-chrome-class-name.js'></script>
<script>

// To generate profile data for analysis with pprof, set generateProfile to
// 'true' and run chrome with "--enable-gpu-benchmarking --no-sandbox".
const generateProfile = false;

// How many targets.
const breadth = 32;
// How many levels of DOM hierarchy above each target.
const depth = 16;
// How many observers.
const redundancy = 1000;

// The total number of observations is breadth * redundancy.

function populate(level) {
  let div = document.createElement('div');
  if (level == 0) {
    div.classList = ['leaf'];
  } else {
    let child = populate(level - 1);
    div.appendChild(child);
  }
  return div;
}

for (let i = 0; i < breadth; i++) {
  document.body.appendChild(populate(depth));
}

for (let i = 0; i < redundancy; i++) {
  let observer = new IntersectionObserver(() => {});
  document.querySelectorAll('.leaf').forEach((target) => { observer.observe(target) });
}

PerfTestRunner.measureFrameTime({
  description: 'Frame time with lots of intersection observers in a deep layer tree.',
  tracingCategories: 'blink',
  traceEventsToMeasure: ['LocalFrameView::UpdateViewportIntersectionsForSubtree'],
  setup: () => {
    document.querySelectorAll('.leaf').forEach(leaf => {
      leaf.innerText = generateChromeClassName();
    });
    // Force layout so that layout cost isn't included in measured time.
    document.querySelector('.leaf').offsetTop;
    if (window.internals)
      internals.clearGeometryMapperCache();
    if (generateProfile && self.chrome && chrome.gpuBenchmarking) {
      chrome.gpuBenchmarking.startProfiling('perf.data');
    }
  },
  run: () => {},
  done: () => {
    if (generateProfile && self.chrome && chrome.gpuBenchmarking) {
      chrome.gpuBenchmarking.stopProfiling();
    }
  }
});
</script>