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<!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>
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