[LargestContentfulPaint] Ignore full viewport images

Bug: 1133883
Change-Id: Id4aac54f834ca7bcf017e8afbbaa4a151d8492b0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2441732
Commit-Queue: Nicolás Peña Moreno <npm@chromium.org>
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Reviewed-by: Annie Sullivan <sullivan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812992}

third_party/blink/renderer/core/paint/image_paint_timing_detector.cc

@@ -137,6 +137,7 @@ ImageRecord* ImagePaintTimingDetector::UpdateCandidate() {
 
 void ImagePaintTimingDetector::OnPaintFinished() {
   frame_index_++;
+  viewport_size_ = base::nullopt;
   if (need_update_timing_at_frame_end_) {
     need_update_timing_at_frame_end_ = false;
     frame_view_->GetPaintTimingDetector()
@@ -297,6 +298,18 @@ uint64_t ImagePaintTimingDetector::ComputeImageRectSize(
   FloatRect float_visual_rect =
       frame_view_->GetPaintTimingDetector().BlinkSpaceToDIPs(
           FloatRect(image_border));
+  if (!viewport_size_.has_value()) {
+    FloatRect viewport = frame_view_->GetPaintTimingDetector().BlinkSpaceToDIPs(
+        FloatRect(frame_view_->GetScrollableArea()->VisibleContentRect()));
+    viewport_size_ = viewport.Size().Area();
+  }
+  // An SVG image size is computed with respect to the virtual viewport of the
+  // SVG, so |rect_size| can be larger than |*viewport_size| in edge cases. If
+  // the rect occupies the whole viewport, disregard this candidate by saying
+  // the size is 0.
+  if (rect_size >= *viewport_size_)
+    return 0;
+
   rect_size = DownScaleIfIntrinsicSizeIsSmaller(
       rect_size, intrinsic_size.Area(),
       float_visual_rect.Width() * float_visual_rect.Height());

third_party/blink/renderer/core/paint/image_paint_timing_detector.h

@@ -10,6 +10,7 @@
 #define THIRD_PARTY_BLINK_RENDERER_CORE_PAINT_IMAGE_PAINT_TIMING_DETECTOR_H_
 
 #include "base/memory/weak_ptr.h"
+#include "base/optional.h"
 #include "third_party/blink/public/web/web_widget_client.h"
 #include "third_party/blink/renderer/core/dom/dom_node_ids.h"
 #include "third_party/blink/renderer/core/loader/resource/image_resource_content.h"
@@ -292,6 +293,10 @@ class CORE_EXPORT ImagePaintTimingDetector final
   void RegisterNotifySwapTime();
   void ReportCandidateToTrace(ImageRecord&);
   void ReportNoCandidateToTrace();
+  // Computes the size of an image for the purpose of LargestContentfulPaint,
+  // downsizing the size of images with low intrinsic size. Images that occupy
+  // the full viewport are special-cased and this method returns 0 for them so
+  // that they are not considered valid candidates.
   uint64_t ComputeImageRectSize(const IntRect&,
                                 const IntSize&,
                                 const PropertyTreeStateOrAlias&,
@@ -317,6 +322,11 @@ class CORE_EXPORT ImagePaintTimingDetector final
   // |FindLargestPaintCandidate| occur during the paint tree walk.
   bool need_update_timing_at_frame_end_ = false;
 
+  // We cache the viewport size computation to avoid performing it on every
+  // image. This value is reset when paint is finished and is computed if unset
+  // when needed. 0 means that the size has not been computed.
+  base::Optional<uint64_t> viewport_size_;
+
   ImageRecordsManager records_manager_;
   Member<LocalFrameView> frame_view_;
   Member<PaintTimingCallbackManager> callback_manager_;

third_party/blink/web_tests/external/wpt/largest-contentful-paint/image-TAO.sub.html

@@ -8,9 +8,7 @@
 <div id='my_div'></div>
 <script>
   async_test(t => {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_implements(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
     const remote_img = 'http://{{domains[www]}}:{{ports[http][1]}}/element-timing/resources/TAOImage.py?'
         + 'origin=' + window.location.origin +'&tao=';
     const valid_tao = ['wildcard', 'origin', 'multi', 'multi_wildcard', 'match_origin', 'match_wildcard'];

third_party/blink/web_tests/external/wpt/largest-contentful-paint/image-full-viewport.html

+<!DOCTYPE HTML>
+<meta charset=utf-8>
+<title>Largest Contentful Paint: size when image overflows</title>
+<!-- In this test, an image with an intrinsic size of 100 x 50 is added, but
+  scaled up in order to overflow the viewport. It should not be reported. -->
+<body>
+<style>
+body {
+  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>
+  const viewportWidth = document.documentElement.clientWidth;
+  const viewportHeight = document.documentElement.clientHeight;
+  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, 'Should have received only one entry!');
+        const entry = entryList.getEntries()[0];
+        if (entry.url)
+          assert_unreached('Should not have received an image entry!');
+      })
+    ).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 = viewportWidth * 2;
+    img.height = viewportHeight * 2;
+    img.onload = () => {
+      const p = document.createElement('p');
+      p.innerHTML = 'a';
+      p.style = 'position: absolute; top: 10px; left: 10px;';
+      document.body.appendChild(p);
+    }
+    document.body.appendChild(img);
+  }, 'The intersectionRect of an img element overflowing is computed correctly');
+</script>
+</body>

third_party/blink/web_tests/external/wpt/largest-contentful-paint/image-inside-svg.html

@@ -6,9 +6,7 @@
 <script src="resources/largest-contentful-paint-helpers.js"></script>
 <script>
 async_test(function (t) {
-  if (!window.PerformanceElementTiming) {
-    assert_unreached("PerformanceElementTiming is not implemented");
-  }
+  assert_implements(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
   const beforeLoad = performance.now();
   new PerformanceObserver(
     t.step_func_done(entryList => {

third_party/blink/web_tests/external/wpt/largest-contentful-paint/image-not-fully-visible.html

 <!DOCTYPE HTML>
 <meta charset=utf-8>
 <title>Largest Contentful Paint: size when image overflows</title>
-<!-- In this test, an image with an intrinsic size of 100 x 50 is added, but
-  scaled up in order to overflow the viewport. -->
 <body>
 <style>
 body {
@@ -19,10 +17,10 @@ body {
   let beforeRender;
   const viewportWidth = document.documentElement.clientWidth;
   const viewportHeight = document.documentElement.clientHeight;
+  const imgWidth = 100;
+  const imgHeight = 50;
   async_test(function (t) {
-    if (!window.PerformanceElementTiming) {
-      assert_unreached("PerformanceElementTiming is not implemented");
-    }
+    assert_implements(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
     const beforeLoad = performance.now();
     new PerformanceObserver(
       t.step_func_done(function(entryList) {
@@ -30,13 +28,13 @@ body {
         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 twice
-        // the viewport width and twice the viewport height, so it is
+        // 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 = 100 / 2;
-        const truncatedHeight = 50 / 2;
+        const truncatedWidth = imgWidth / 2;
+        const truncatedHeight = imgHeight / 2;
         const weightedSize = truncatedWidth * truncatedHeight;
         checkImage(entry, url, 'image_id', weightedSize, beforeLoad);
       })
@@ -45,8 +43,11 @@ body {
     img = document.createElement('img');
     img.src = '/images/green-100x50.png';
     img.id = 'image_id';
-    img.width = viewportWidth * 2;
-    img.height = viewportHeight * 2;
+    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>

third_party/blink/web_tests/external/wpt/largest-contentful-paint/observe-text.html

@@ -34,7 +34,7 @@ p {
     );
     observer.observe({type: 'largest-contentful-paint', buffered: true});
     beforeRender = performance.now();
-  }, 'Element with elementtiming attribute is observable.');
+  }, 'Text element is observable as a LargestContentfulPaint candidate.');
 </script>
 
 <p id='my_text'>This is important text! :)</p>

third_party/blink/web_tests/external/wpt/largest-contentful-paint/resources/largest-contentful-paint-helpers.js

-// Receives an image PerformanceElementTiming |entry| and checks |entry|'s attribute values.
+// 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:
 // * 'renderTimeIs0': the renderTime should be 0 (image does not pass Timing-Allow-Origin checks).