1 files changed, 54 insertions, 0 deletions
diff --git a/testing/web-platform/tests/largest-contentful-paint/image-not-fully-visible.html b/testing/web-platform/tests/largest-contentful-paint/image-not-fully-visible.html
new file mode 100644
index 0000000000..8990fd14c0
--- /dev/null
+++ b/testing/web-platform/tests/largest-contentful-paint/image-not-fully-visible.html
@@ -0,0 +1,54 @@
+<!DOCTYPE HTML>
+<meta charset=utf-8>
+<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>
+  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/green-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/green-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>