<!DOCTYPE HTML>
<meta charset=utf-8>
<meta name="viewport" content="width=device-width, minimum-scale=1">
<title>Largest Contentful Paint: size when image overflows</title>
<body>
<style>
body {
/* Preventing a scrollbar from showing and removing any margins simplifies
the calculations below. */
overflow: hidden;
margin: 0px;
}
</style>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="resources/largest-contentful-paint-helpers.js"></script>
<script>
setup({"hide_test_state": true});
let beforeRender;
const viewportWidth = document.documentElement.clientWidth;
const viewportHeight = document.documentElement.clientHeight;
const imgWidth = 100;
const imgHeight = 50;
async_test(function (t) {
assert_implements(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
const beforeLoad = performance.now();
new PerformanceObserver(
t.step_func_done(function(entryList) {
assert_equals(entryList.getEntries().length, 1);
const entry = entryList.getEntries()[0];
const url = window.location.origin + '/images/lcp-100x50.png';
// To compute the size, compute the percentage of the image visible and
// scale by its natural dimensions. In this test, the image is expanded to twice its size
// but place towards the bottom right corner of the viewport, so it is
// effectively clipped to 50% by 50% of its display size. Scaling by
// its natural width and height of 100px and 50px respectively, leads
// to a weighted size of 50 by 25.
const truncatedWidth = imgWidth / 2;
const truncatedHeight = imgHeight / 2;
const weightedSize = truncatedWidth * truncatedHeight;
checkImage(entry, url, 'image_id', weightedSize, beforeLoad);
})
).observe({type: 'largest-contentful-paint', buffered: true});
// Add an image, setting width and height equal to viewport.
img = document.createElement('img');
img.src = '/images/lcp-100x50.png';
img.id = 'image_id';
img.width = imgWidth * 2;
img.height = imgHeight * 2;
img.style.position = 'absolute';
img.style.left = viewportWidth - imgWidth + 'px';
img.style.top = viewportHeight - imgHeight + 'px';
document.body.appendChild(img);
}, 'The intersectionRect of an img element overflowing is computed correctly');
</script>
</body>
Codebase Browser
chromium