<!DOCTYPE html>
<title>Layout Instability: element with compositing layer hint</title>
<link rel="help" href="https://wicg.github.io/layout-instability/" />
<style>

#shift {
  position: relative;
  width: 500px;
  height: 200px;
  background: yellow;
}
#container {
  position: absolute;
  width: 350px;
  height: 400px;
  right: 50px;
  top: 100px;
  background: #ccc;
}
.promote { will-change: transform; }

</style>
<div id="container" class="promote">
  <div id="space"></div>
  <div id="shift" class="promote"></div>
</div>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="resources/util.js"></script>
<script>

promise_test(async () => {
  const watcher = new ScoreWatcher;

  // Wait for the initial render to complete.
  await waitForAnimationFrames(2);

  // Induce a shift.
  document.querySelector("#space").style = "height: 100px";

  // #shift is 400x200 after viewport intersection with correct application of
  // composited #container offset, and 100px lower after shifting, so impact
  // region is 400 * (200 + 100).
  const expectedScore = computeExpectedScore(400 * (200 + 100), 100);

  // Observer fires after the frame is painted.
  assert_equals(watcher.score, 0);
  await watcher.promise;
  assert_equals(watcher.score, expectedScore);
}, "Element with compositing layer hint.");

</script>
