mozilla-central/testing/web-platform/tests/paint-timing/fcp-only/fcp-document-opacity-image.html

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Test Info: Warnings

<!DOCTYPE html>
<html class="hide">
<head>
<title>Performance Paint Timing Test: Image FCP due to the documentElement's opacity</title>
<style>
html {
will-change: opacity;
}
.hide {
opacity: 0;
}
</style>
</head>
<body>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="../resources/utils.js"></script>
<div id="main"></div>
<script>
// Load the image, add it to the DOM and make sure it's decoded.
const load_image = () => {
const img = document.createElement("img");
img.src = "../resources/circles.png";
document.body.appendChild(img);
return img.decode();
};
const change_opacity = () => {
document.documentElement.className = "";
}
promise_test(async t => {
assert_implements(window.PerformancePaintTiming, "Paint Timing isn't supported.");
await load_image();
await assertNoFirstContentfulPaint(t);
change_opacity();
await waitForAnimationFrames(3);
const fcp_entries = performance.getEntriesByName('first-contentful-paint');
assert_equals(fcp_entries.length, 1, "Got an FCP entry");
const lcp_entries = await new Promise(resolve => {new PerformanceObserver((list) => resolve(list.getEntries())).observe({type: 'largest-contentful-paint', buffered: true})});
assert_equals(lcp_entries.length, 1, "Got an LCP entry");
// TODO: Rewrite this assertion after the FCP and LCP precision alignment CL is landed. Currently FCP start time has a higher precision than that of LCP. That means, even if the two are intrinsically the same, FCP.startTime will be larger as it has more fractional digits.
isLess = fcp_entries[0].startTime < lcp_entries[0].startTime;
isEqualToMicrosecond = Math.abs(fcp_entries[0].startTime - lcp_entries[0].startTime) < 0.001;
assert_true(isLess || isEqualToMicrosecond, "FCP should be smaller than FCP.");
}, "Test that FCP after opacity change is not a larger value than LCP");
</script>
</body>
</html>