[LCP] Add animated image support

This CL adds support for better handling of animated images in LCP: * A new attribute is exposing the first animated frame's paint time (behind a flag). * `startTime` is not changed. * The PageLoadMetrics reported for LCP are set to that first frame paint time for animated images (behind another flag). * Entries are not emitted until the image is loaded. Relevant spec issue: w3c/largest-contentful-paint#83 Change-Id: I6bb01eacb4f200f9c032ffcfcd9a1a41126a7773 Bug: 1260953
web-platform-tests · Oct 26, 2021 · d993fee · d993fee
1 parent 1b3124b
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diff --git a/images/anim-tao.png b/images/anim-tao.png
diff --git a/images/anim-tao.png.headers b/images/anim-tao.png.headers
@@ -0,0 +1,2 @@
+Timing-Allow-Origin: *
+
diff --git a/images/webp-animated.webp b/images/webp-animated.webp
diff --git a/largest-contentful-paint/animated/observe-animated-image-gif.tentative.html b/largest-contentful-paint/animated/observe-animated-image-gif.tentative.html
@@ -0,0 +1,27 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset=utf-8>
+  <title>Largest Contentful Paint: observe image.</title>
+  <script src="/resources/testharness.js"></script>
+  <script src="/resources/testharnessreport.js"></script>
+  <script src="../resources/largest-contentful-paint-helpers.js"></script>
+</head>
+<body>
+  <script>
+    promise_test(async () => {
+      assert_implements(window.LargestContentfulPaint,
+                        "LargestContentfulPaint is not implemented");
+      const beforeLoad = performance.now();
+      // 136 is the size of the animated GIF up until the first frame.
+      // The trickle pipe delays the response after the first frame by 1 second.
+      const url = window.location.origin +
+                  `/images/anim-gr.gif?pipe=trickle(136:d${delay_pipe_value})`;
+      const entry = await load_and_observe(url);
+      // anim-gr.gif is 100 by 50.
+      const size = 100 * 50;
+      checkImage(entry, url, 'image_id', size, beforeLoad, ["animated"]);
+    }, "Same origin animated image is observable and has a first frame.");
+  </script>
+</body>
+</html>
diff --git a/largest-contentful-paint/animated/observe-animated-image-webp.tentative.html b/largest-contentful-paint/animated/observe-animated-image-webp.tentative.html
@@ -0,0 +1,27 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset=utf-8>
+  <title>Largest Contentful Paint: observe image.</title>
+  <script src="/resources/testharness.js"></script>
+  <script src="/resources/testharnessreport.js"></script>
+  <script src="../resources/largest-contentful-paint-helpers.js"></script>
+</head>
+<body>
+  <script>
+    promise_test(async () => {
+      assert_implements(window.LargestContentfulPaint,
+                        "LargestContentfulPaint is not implemented");
+      const beforeLoad = performance.now();
+      // 142 is the size of the animated WebP up until the first frame.
+      // The trickle pipe delays the response after the first frame by 1 second.
+      const url = window.location.origin +
+        `/images/webp-animated.webp?pipe=trickle(142:d${delay_pipe_value})`;
+      const entry = await load_and_observe(url);
+      // webp-animated.webp is 11 by 29.
+      const size = 11 * 29;
+      checkImage(entry, url, 'image_id', size, beforeLoad, ["animated"]);
+    }, "Same origin animated image is observable and has a first frame.");
+  </script>
+</body>
+</html>
diff --git a/largest-contentful-paint/animated/observe-animated-image.tentative.html b/largest-contentful-paint/animated/observe-animated-image.tentative.html
@@ -0,0 +1,29 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset=utf-8>
+  <title>Largest Contentful Paint: observe image.</title>
+  <script src="/resources/testharness.js"></script>
+  <script src="/resources/testharnessreport.js"></script>
+  <script src="../resources/largest-contentful-paint-helpers.js"></script>
+</head>
+<body>
+  <script>
+    promise_test(async () => {
+      assert_implements(window.LargestContentfulPaint,
+                        "LargestContentfulPaint is not implemented");
+      const beforeLoad = performance.now();
+      // 262 is the size of the animated PNG up until the first frame,
+      // including the chunk that starts the second frame (indicating that
+      // the first frame data is done).
+      // The trickle pipe delays the response after the first frame by 1 second.
+      const url = window.location.origin +
+                  `/images/anim-gr.png?pipe=trickle(262:d${delay_pipe_value})`;
+      const entry = await load_and_observe(url);
+      // anim-gr.png is 100 by 50.
+      const size = 100 * 50;
+      checkImage(entry, url, 'image_id', size, beforeLoad, ["animated"]);
+    }, "Same origin animated image is observable and has a first frame.");
+  </script>
+</body>
+</html>
diff --git a/largest-contentful-paint/animated/observe-cross-origin-animated-image.tentative.html b/largest-contentful-paint/animated/observe-cross-origin-animated-image.tentative.html
@@ -0,0 +1,30 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset=utf-8>
+  <title>Largest Contentful Paint: observe image.</title>
+  <script src="/resources/testharness.js"></script>
+  <script src="/resources/testharnessreport.js"></script>
+  <script src="../resources/largest-contentful-paint-helpers.js"></script>
+  <script src="/common/get-host-info.sub.js"></script>
+</head>
+<body>
+  <script>
+    promise_test(async () => {
+      assert_implements(window.LargestContentfulPaint,
+                        "LargestContentfulPaint is not implemented");
+      const beforeLoad = performance.now();
+      // 262 is the size of the animated PNG up until the first frame,
+      // including the chunk that starts the second frame (indicating that
+      //the first frame data is done).
+      const {REMOTE_ORIGIN} = get_host_info();
+      const url = REMOTE_ORIGIN +
+                  '/images/anim-gr.png?pipe=trickle(262:d1)';
+      const entry = await load_and_observe(url);
+      // anim-gr.png is 100 by 50.
+      const size = 100 * 50;
+      checkImage(entry, url, 'image_id', size, beforeLoad, ["renderTimeIs0", "animated-zero"]);
+    }, "Same origin animated image is observable and has a first frame.");
+  </script>
+</body>
+</html>
diff --git a/largest-contentful-paint/animated/observe-cross-origin-tao-animated-image.tentative.html b/largest-contentful-paint/animated/observe-cross-origin-tao-animated-image.tentative.html
@@ -0,0 +1,30 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset=utf-8>
+  <title>Largest Contentful Paint: observe image.</title>
+  <script src="/resources/testharness.js"></script>
+  <script src="/resources/testharnessreport.js"></script>
+  <script src="../resources/largest-contentful-paint-helpers.js"></script>
+  <script src="/common/get-host-info.sub.js"></script>
+</head>
+<body>
+  <script>
+    promise_test(async () => {
+      assert_implements(window.LargestContentfulPaint,
+                        "LargestContentfulPaint is not implemented");
+      const beforeLoad = performance.now();
+      // 262 is the size of the animated PNG up until the first frame,
+      // including the chunk that starts the second frame (indicating that
+      //the first frame data is done).
+      const {REMOTE_ORIGIN} = get_host_info();
+      const url = REMOTE_ORIGIN +
+                  '/images/anim-tao.png?pipe=trickle(262:d1)';
+      const entry = await load_and_observe(url);
+      // anim-gr.png is 100 by 50.
+      const size = 100 * 50;
+      checkImage(entry, url, 'image_id', size, beforeLoad, ["animated"]);
+    }, "Same origin animated image is observable and has a first frame.");
+  </script>
+</body>
+</html>
diff --git a/largest-contentful-paint/animated/observe-non-animated-image.tentative.html b/largest-contentful-paint/animated/observe-non-animated-image.tentative.html
@@ -0,0 +1,27 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset=utf-8>
+  <title>Largest Contentful Paint: observe image.</title>
+  <script src="/resources/testharness.js"></script>
+  <script src="/resources/testharnessreport.js"></script>
+  <script src="../resources/largest-contentful-paint-helpers.js"></script>
+</head>
+<body>
+  <script>
+    promise_test(async () => {
+      assert_implements(window.LargestContentfulPaint,
+                        "LargestContentfulPaint is not implemented");
+      const beforeLoad = performance.now();
+      // 262 is the size of the animated PNG up until the first frame,
+      // including the chunk that starts the second frame (indicating that
+      //the first frame data is done).
+      const url = window.location.origin + '/images/blue.png';
+      const entry = await load_and_observe(url);
+      // blue.png is 133 by 106.
+      const size = 133 * 106;
+      checkImage(entry, url, 'image_id', size, beforeLoad, ["animated-zero"]);
+    }, "Same origin animated image is observable and has a first frame.");
+  </script>
+</body>
+</html>
diff --git a/largest-contentful-paint/resources/largest-contentful-paint-helpers.js b/largest-contentful-paint/resources/largest-contentful-paint-helpers.js
@@ -1,3 +1,6 @@
+const image_delay = 1000;
+const delay_pipe_value = image_delay / 1000;
+
 // Receives an image LargestContentfulPaint |entry| and checks |entry|'s attribute values.
 // The |timeLowerBound| parameter is a lower bound on the loadTime value of the entry.
 // The |options| parameter may contain some string values specifying the following:
@@ -33,4 +36,33 @@ function checkImage(entry, expectedUrl, expectedID, expectedSize, timeLowerBound
   } else {
     assert_equals(entry.size, expectedSize);
   }
+  if (options.includes('animated')) {
+    assert_greater_than(entry.loadTime, entry.firstAnimatedFrameTime,
+      'firstAnimatedFrameTime should be smaller than loadTime');
+    assert_greater_than(entry.renderTime, entry.firstAnimatedFrameTime,
+      'firstAnimatedFrameTime should be smaller than renderTime');
+    assert_less_than(entry.firstAnimatedFrameTime, image_delay,
+      'firstAnimatedFrameTime should be smaller than the delay applied to the second frame');
+    assert_greater_than(entry.firstAnimatedFrameTime, 0,
+      'firstAnimatedFrameTime should be larger than 0');
+  }
+  if (options.includes('animated-zero')) {
+    assert_equals(entry.firstAnimatedFrameTime, 0, 'firstAnimatedFrameTime should be 0');
+  }
 }
+
+const load_and_observe = url => {
+  return new Promise(resolve => {
+    (new PerformanceObserver(entryList => {
+      for (let entry of entryList.getEntries()) {
+        if (entry.url == url) {
+          resolve(entryList.getEntries()[0]);
+        }
+      }
+    })).observe({type: 'largest-contentful-paint', buffered: true});
+    const img = new Image();
+    img.id = 'image_id';
+    img.src = url;
+    document.body.appendChild(img);
+  });
+};