From 7b2e3f7ff30d5dcf17cd5c00f0554a44eec2c2a1 Mon Sep 17 00:00:00 2001
From: Stefan Zager <szager@chromium.org>
Date: Thu, 24 Oct 2024 02:35:39 +0000
Subject: [PATCH] IntersectionObserver -- properly handle "unknown" occlusion state

If we most recently reported a target as "guaranteed visible", then in
the interest of avoiding false positives we must transition to "not
guaranteed visible" if the frame occlusion state becomes "unknown".

This CL also makes a child frame inherit its parent's "not visible"
occlusion state rather than calling it "unknown", which is technically
more correct.

Bug: chromium:371247941
Change-Id: I4d721dd252d013deac14a12f1f2922830ef2a8a4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5950965
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Commit-Queue: Stefan Zager <szager@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1373093}
---

diff --git a/third_party/blink/renderer/core/frame/frame_view.cc b/third_party/blink/renderer/core/frame/frame_view.cc
index 3d6d9a2..29981ce52 100644
--- a/third_party/blink/renderer/core/frame/frame_view.cc
+++ b/third_party/blink/renderer/core/frame/frame_view.cc
@@ -77,15 +77,20 @@
   gfx::Transform main_frame_transform_matrix;
   DocumentLifecycle::LifecycleState parent_lifecycle_state =
       owner_document.Lifecycle().GetState();
+
+  bool should_compute_occlusion = false;
   mojom::blink::FrameOcclusionState occlusion_state =
       owner_document.GetFrame()->GetOcclusionState();
-  bool should_compute_occlusion =
-      needs_occlusion_tracking &&
-      occlusion_state ==
-          mojom::blink::FrameOcclusionState::kGuaranteedNotOccluded &&
-      parent_lifecycle_state >= DocumentLifecycle::kPrePaintClean;
-  if (!should_compute_occlusion) {
+  if (occlusion_state ==
+      mojom::blink::FrameOcclusionState::kGuaranteedNotOccluded) {
+    // We can't propagate kGuaranteedNotOccluded from the parent without testing
+    // occlusion of this frame. If we don't ultimately do an occlusion test on
+    // this frame, then we should propagate "unknown".
     occlusion_state = mojom::blink::FrameOcclusionState::kUnknown;
+    if (needs_occlusion_tracking &&
+        parent_lifecycle_state >= DocumentLifecycle::kPrePaintClean) {
+      should_compute_occlusion = true;
+    }
   }
 
   LayoutEmbeddedContent* owner_layout_object =
@@ -159,8 +164,12 @@
         rect_in_parent_stable_since_for_iov2_ = base::TimeTicks::Now();
       }
     }
-    if (should_compute_occlusion && !geometry.IsVisible())
-      occlusion_state = mojom::blink::FrameOcclusionState::kPossiblyOccluded;
+    if (should_compute_occlusion) {
+      occlusion_state =
+          geometry.IsVisible()
+              ? mojom::blink::FrameOcclusionState::kGuaranteedNotOccluded
+              : mojom::blink::FrameOcclusionState::kPossiblyOccluded;
+    }
 
     // Generate matrix to transform from the space of the containing document
     // to the space of the iframe's contents.
@@ -248,11 +257,6 @@
     }
     main_frame_transform_matrix =
         child_frame_to_root_frame.AccumulatedTransform();
-  } else if (occlusion_state ==
-             mojom::blink::FrameOcclusionState::kGuaranteedNotOccluded) {
-    // If the parent LocalFrameView is throttled and out-of-date, then we can't
-    // get any useful information.
-    occlusion_state = mojom::blink::FrameOcclusionState::kUnknown;
   }
 
   // An iframe's content is always pixel-snapped, even if the iframe element has
diff --git a/third_party/blink/renderer/core/intersection_observer/intersection_observation.cc b/third_party/blink/renderer/core/intersection_observer/intersection_observation.cc
index a05620d..160254b6 100644
--- a/third_party/blink/renderer/core/intersection_observer/intersection_observation.cc
+++ b/third_party/blink/renderer/core/intersection_observer/intersection_observation.cc
@@ -179,11 +179,14 @@
       Observer()->trackVisibility()) {
     mojom::blink::FrameOcclusionState occlusion_state =
         target_->GetDocument().GetFrame()->GetOcclusionState();
-    // If we're tracking visibility, and we don't have occlusion information
-    // from our parent frame, then postpone computing intersections until a
-    // later lifecycle when the occlusion information is known.
-    if (occlusion_state == mojom::blink::FrameOcclusionState::kUnknown)
+    // If we're tracking visibility, and we aren't currently reporting the
+    // target visible, and we don't have occlusion information from our parent
+    // frame, then postpone computing intersections until a later lifecycle when
+    // the occlusion information is known.
+    if (!last_is_visible_ &&
+        occlusion_state == mojom::blink::FrameOcclusionState::kUnknown) {
       return false;
+    }
   }
   return true;
 }
diff --git a/third_party/blink/web_tests/external/wpt/intersection-observer/resources/v2-midframe.sub.html b/third_party/blink/web_tests/external/wpt/intersection-observer/resources/v2-midframe.sub.html
new file mode 100644
index 0000000..b9b055b6
--- /dev/null
+++ b/third_party/blink/web_tests/external/wpt/intersection-observer/resources/v2-midframe.sub.html
@@ -0,0 +1,18 @@
+<!DOCTYPE html>
+<style>
+iframe {
+  width: 300px;
+  height: 150px;
+  border: none;
+}
+</style>
+
+<iframe src="http://{{domains[www2]}}:{{ports[http][0]}}/intersection-observer/resources/v2-subframe.html"></iframe>
+
+<script>
+window.addEventListener("message", event => {
+  requestAnimationFrame(() => setTimeout(() => {
+    document.querySelector('iframe').contentWindow.postMessage(event.data, "*");
+  }));
+});
+</script>
diff --git a/third_party/blink/web_tests/external/wpt/intersection-observer/resources/v2-subframe.html b/third_party/blink/web_tests/external/wpt/intersection-observer/resources/v2-subframe.html
index 295bbf04..cfc82646 100644
--- a/third_party/blink/web_tests/external/wpt/intersection-observer/resources/v2-subframe.html
+++ b/third_party/blink/web_tests/external/wpt/intersection-observer/resources/v2-subframe.html
@@ -16,7 +16,7 @@
 
 window.addEventListener("message", event => {
   waitForNotification(() => {
-    window.parent.postMessage(results.map(e => e.isVisible), "*");
+    window.top.postMessage(results.map(e => e.isVisible), "*");
     results = [];
   });
 });
@@ -27,6 +27,6 @@
     results = entries;
   }, {trackVisibility: true, delay: delay});
   observer.observe(document.getElementById("target"));
-  window.parent.postMessage("", "*");
+  window.top.postMessage("", "*");
 };
 </script>
diff --git a/third_party/blink/web_tests/external/wpt/intersection-observer/v2/nested-cross-origin.sub.html b/third_party/blink/web_tests/external/wpt/intersection-observer/v2/nested-cross-origin.sub.html
new file mode 100644
index 0000000..42a69bf
--- /dev/null
+++ b/third_party/blink/web_tests/external/wpt/intersection-observer/v2/nested-cross-origin.sub.html
@@ -0,0 +1,61 @@
+<!DOCTYPE html>
+<meta name="viewport" content="width=device-width,initial-scale=1">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="../resources/intersection-observer-test-utils.js"></script>
+
+<style>
+pre, #log {
+  position: absolute;
+  top: 0;
+  left: 200px;
+}
+iframe {
+  width: 300px;
+  height: 150px;
+  border: none;
+}
+</style>
+
+<iframe src="http://{{domains[www1]}}:{{ports[http][0]}}/intersection-observer/resources/v2-midframe.sub.html"></iframe>
+
+<script>
+async_test(function(t) {
+  let iframe = document.querySelector("iframe");
+
+  function step0(event) {
+    assert_equals(event.data,"");
+  }
+
+  function step1(event) {
+    assert_equals(JSON.stringify(event.data),
+                  JSON.stringify([true]));
+    iframe.style.opacity = "0.9";
+  }
+
+  function step2(event) {
+    assert_equals(JSON.stringify(event.data),
+                  JSON.stringify([false]));
+    iframe.style.opacity = "";
+  }
+
+  function step3(event) {
+    assert_equals(JSON.stringify(event.data),
+                  JSON.stringify([true]));
+  }
+
+  let steps = [step0, step1, step2, step3];

diff --git a/third_party/blink/web_tests/external/wpt/intersection-observer/resources/v2-midframe.sub.html b/third_party/blink/web_tests/external/wpt/intersection-observer/resources/v2-midframe.sub.html
new file mode 100644
index 0000000..b9b055b6
--- /dev/null
+++ b/third_party/blink/web_tests/external/wpt/intersection-observer/resources/v2-midframe.sub.html
@@ -0,0 +1,18 @@
+<!DOCTYPE html>
+<style>
+iframe {
+  width: 300px;
+  height: 150px;
+  border: none;
+}
+</style>
+
+<iframe src="http://{{domains[www2]}}:{{ports[http][0]}}/intersection-observer/resources/v2-subframe.html"></iframe>
+
+<script>
+window.addEventListener("message", event => {
+  requestAnimationFrame(() => setTimeout(() => {
+    document.querySelector('iframe').contentWindow.postMessage(event.data, "*");
+  }));
+});
+</script>
diff --git a/third_party/blink/web_tests/external/wpt/intersection-observer/resources/v2-subframe.html b/third_party/blink/web_tests/external/wpt/intersection-observer/resources/v2-subframe.html
index 295bbf04..cfc82646 100644
--- a/third_party/blink/web_tests/external/wpt/intersection-observer/resources/v2-subframe.html
+++ b/third_party/blink/web_tests/external/wpt/intersection-observer/resources/v2-subframe.html
@@ -16,7 +16,7 @@
 
 window.addEventListener("message", event => {
   waitForNotification(() => {
-    window.parent.postMessage(results.map(e => e.isVisible), "*");
+    window.top.postMessage(results.map(e => e.isVisible), "*");
     results = [];
   });
 });
@@ -27,6 +27,6 @@
     results = entries;
   }, {trackVisibility: true, delay: delay});
   observer.observe(document.getElementById("target"));
-  window.parent.postMessage("", "*");
+  window.top.postMessage("", "*");
 };
 </script>
diff --git a/third_party/blink/web_tests/external/wpt/intersection-observer/v2/nested-cross-origin.sub.html b/third_party/blink/web_tests/external/wpt/intersection-observer/v2/nested-cross-origin.sub.html
new file mode 100644
index 0000000..42a69bf
--- /dev/null
+++ b/third_party/blink/web_tests/external/wpt/intersection-observer/v2/nested-cross-origin.sub.html
@@ -0,0 +1,61 @@
+<!DOCTYPE html>
+<meta name="viewport" content="width=device-width,initial-scale=1">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="../resources/intersection-observer-test-utils.js"></script>
+
+<style>
+pre, #log {
+  position: absolute;
+  top: 0;
+  left: 200px;
+}
+iframe {
+  width: 300px;
+  height: 150px;
+  border: none;
+}
+</style>
+
+<iframe src="http://{{domains[www1]}}:{{ports[http][0]}}/intersection-observer/resources/v2-midframe.sub.html"></iframe>
+
+<script>
+async_test(function(t) {
+  let iframe = document.querySelector("iframe");
+
+  function step0(event) {
+    assert_equals(event.data,"");
+  }
+
+  function step1(event) {
+    assert_equals(JSON.stringify(event.data),
+                  JSON.stringify([true]));
+    iframe.style.opacity = "0.9";
+  }
+
+  function step2(event) {
+    assert_equals(JSON.stringify(event.data),
+                  JSON.stringify([false]));
+    iframe.style.opacity = "";
+  }
+
+  function step3(event) {
+    assert_equals(JSON.stringify(event.data),
+                  JSON.stringify([true]));
+  }
+
+  let steps = [step0, step1, step2, step3];
+
+  window.addEventListener("message", event => {
+    if (steps.length) {
+      t.step(steps.shift(), t, event);
+      waitForFrame(t, () => {
+        iframe.contentWindow.postMessage("", "*");
+      });
+    } else {
+      t.done();
+    }
+  });
+
+}, "Intersection observer V2 test with nested cross-origin iframes.");
+</script>