Bug 1979223 [wpt PR 53971] - WebKit export of https://bugs.webkit.org/show_bug.cgi?id=290993, a=testonly

Automatic update from web-platform-tests
WebKit export of https://bugs.webkit.org/show_bug.cgi?id=290993 (#53971)

--

wpt-commits: 90baf42ec656dacc24a35d1c7dc7ab6734a4fff2
wpt-pr: 53971

UltraBlame original commit: 665bf8ee74f53c4e0b6fa581fb2e2cf88646b1e7

Author: marco-c

testing/web-platform/tests/web-animations/timing-model/animations/setting-the-start-time-of-an-animation.html

@@ -325,5 +325,58 @@
 }, 'Setting the start time on a reverse running animation updates the play '
    + 'state');
 
+promise_test(async t => {
+  const make_animation = () => createDiv(t).animate(null, 100 * MS_PER_SEC);
+
+  // Wait for a couple of page rendering updates to run and record the timeline time.
+  await waitForAnimationFrames(2);
+  const timelineTimeForFirstPageRenderingUpdate = document.timeline.currentTime;
+
+  // Create a first animation that is created during the page rendering update.
+  // This animation should have its start time set to the current timeline time.
+  const animStartedDuringPageRenderingUpdate = make_animation();
+
+  // Wait for a new JS call frame and start another animation. This animation
+  // should have its start time set to the timeline time of the next page
+  // rendering update.
+  await new Promise(setTimeout);
+  const animStartedAfterTimeout = make_animation();
+
+  // Wait for another new JS call frame and start another animation. This
+  // animation, like the previous one, should have its start time set to
+  // the timeline time of the next page rendering update.
+  await new Promise(setTimeout);
+  const animStartedAfterAnotherTimeout = make_animation();
+
+  // Now wait until the next page rendering update and record the timeline time.
+  await waitForAnimationFrames(1);
+  const timelineTimeForSecondPageRenderingUpdate = document.timeline.currentTime;
+
+  // Create an animation that is created during this second page rendering update.
+  // This animation should have its start time set to the new timeline time.
+  const animStartedDuringSecondPageRenderingUpdate = make_animation();
+
+  // All animations should be ready by the next animation frame.
+  await waitForAnimationFrames(1);
+
+  const assert_start_time = (animation, expected, description) => {
+    assert_approx_equals(animation.startTime, expected, 0.0001,
+      `Start time of animation started ${description}`);
+  };
+
+  assert_start_time(animStartedDuringPageRenderingUpdate,
+    timelineTimeForFirstPageRenderingUpdate,
+    "during the first page rendering update");
+  assert_start_time(animStartedAfterTimeout,
+    timelineTimeForSecondPageRenderingUpdate,
+    "after waiting for a new JS call frame");
+  assert_start_time(animStartedAfterAnotherTimeout,
+    timelineTimeForSecondPageRenderingUpdate,
+    "after waiting for another new JS call frame");
+  assert_start_time(animStartedDuringSecondPageRenderingUpdate,
+    timelineTimeForSecondPageRenderingUpdate,
+    "during the second page rendering update");
+}, 'Checking the start time of animations started at various times between two page rendering updates');
+
 </script>
 </body>