containertiming-largest-painted-element.html

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This WPT test may be referenced by the following Test IDs:
- /container-timing/tentative/containertiming-largest-painted-element.html - WPT Dashboard Interop Dashboard

<!DOCTYPE HTML>

<meta charset=utf-8>

<title>Container Timing: lastPaintedElement is the largest element, not the last painted</title>

<body>

<style>

body {

  margin: 0;

</style>

<script src="/resources/testharness.js"></script>

<script src="/resources/testharnessreport.js"></script>

<script src="/container-timing/resources/container-timing-helpers.js"></script>

<script>

  let beforeRender;

  async_test(function (t) {

    assert_implements(window.PerformanceContainerTiming, "PerformanceContainerTiming is not implemented");

    const observer = new PerformanceObserver(

      t.step_func_done(function(entryList) {

        assert_equals(entryList.getEntries().length, 1);

        const entry = entryList.getEntries()[0];

        // The small image is painted last, but the big one has the largest area

        // of its own, so it is the one reported.

        checkContainerEntry(entry, 'div_ct', 'big_id', beforeRender)

        checkContainerIntersectionRect(entry, [0, 240, 0, 240])

        checkContainerSize(entry, 11600);

})

);

    observer.observe({entryTypes: ['container']});

    // Add a div that is the container timing root

    const div = document.createElement('div');

    div.setAttribute('containertiming', 'div_ct');

    document.body.appendChild(div);

    // 100x100 = 10000 for the big one, 40x40 = 1600 for the small one.

    const big = document.createElement('img');

    big.src = '/container-timing/resources/square100.png';

    big.setAttribute('id', 'big_id');

    big.style.position = 'absolute';

    big.style.left = '0px';

    big.style.top = '0px';

    big.style.width = '100px';

    big.style.height = '100px';

    div.appendChild(big);

    const small = document.createElement('img');

    small.src = '/container-timing/resources/square100.png';

    small.setAttribute('id', 'small_id');

    small.style.position = 'absolute';

    small.style.left = '200px';

    small.style.top = '200px';

    small.style.width = '40px';

    small.style.height = '40px';

    div.appendChild(small);

    beforeRender = performance.now();

  }, 'lastPaintedElement reports the largest element painted.');

</script>

</body>