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[animation-trigger] Don't update attachments if layout is needed #56989

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Merged
chromium-wpt-export-bot merged 1 commit into from
Jan 5, 2026
Merged

[animation-trigger] Don't update attachments if layout is needed #56989

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145 changes: 145 additions & 0 deletions scroll-animations/animation-trigger/timeline-trigger-toggle.tentative.html
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Original file line number Diff line number Diff line change
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<!DOCTYPE html>
<html>

<head>
<link rel="help" src="https://drafts.csswg.org/css-animations-2/#animation-trigger">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/web-animations/testcommon.js"></script>
<script src="/dom/events/scrolling/scroll_support.js"></script>
<script src="support/support.js"></script>
</head>

<body>
<style>
@keyframes expand {
from {
width: 100px;
}

to {
width: 100px;
}
}

#scroller {
width: 300px;
height: 300px;
overflow: scroll;
}

#source {
height: 100px;
width: 100px;
background-color: seagreen;
}

.trigger-source {
timeline-trigger: --trigger view() contain;
}

.blob {
height: 50px;
background-color: lightgrey;
}

.blob:nth-child(even) {
background-color: darkgrey;
}

#target {
background-color: tomato;
position: absolute;
animation: expand linear 1s both;
animation-trigger: --trigger play-forwards play-backwards;
width: 50px;
}
</style>
<div id=scroller>
<div class=blob></div>
<div class=blob></div>
<div id=source>Source</div>
<div id=target>Target</div>
<div class=blob></div>
<div class=blob></div>
<div class=blob></div>
<div class=blob></div>
<div class=blob></div>
<div class=blob></div>
</div>
<hr>
<button id=button>Toggle timeline-trigger</button>
<pre id=pre></pre>
<hr>
<script>
const scroller = document.getElementById("scroller");
const source = document.getElementById("source");
const target = document.getElementById("target");
const animation = target.getAnimations()[0];

async function scrollSourceOutOfView() {
// First, scroll source to the top of the viewport.
let scrollend_promise =
waitForScrollEndFallbackToDelayWithoutScrollEvent(scroller);
source.scrollIntoView({block: "start"});
await scrollend_promise;
// Now scroll a litte further to push it just out of view.
scrollend_promise =
waitForScrollEndFallbackToDelayWithoutScrollEvent(scroller);
scroller.scrollBy({top: 50});
await scrollend_promise;
await waitForCompositorCommit();
}

async function scrollSourceIntoView() {
let scrollend_promise =
waitForScrollEndFallbackToDelayWithoutScrollEvent(scroller);
source.scrollIntoView({block: "center"});
await scrollend_promise;
await waitForCompositorCommit();
}

promise_test(async(test) => {
assert_equals(getComputedStyle(source).timelineTrigger, "none");
assert_equals(animation.playState, "paused");

// Toggle the trigger on.
source.style.timelineTrigger = "--trigger view() contain";
assert_equals(getComputedStyle(source).timelineTrigger,
"--trigger view() contain");
await waitForCompositorCommit();

// Animation should be playing forwards as source is already in view.
assert_equals(animation.playState, "running");

// Simulate the animation finishing (instead of stalling the test).
animation.finish();
assert_equals(animation.playState, "finished");

await scrollSourceOutOfView();
// Animation should be playing backwards.
assert_equals(animation.playState, "running");

// Simulate the backwards finish.
animation.finish();
assert_equals(animation.playState, "finished");
assert_equals(animation.currentTime, 0);

// Toggle the trigger off.
source.style.timelineTrigger = "initial";
assert_equals(getComputedStyle(source).timelineTrigger, "none");
await waitForCompositorCommit();

// There should be no change to the animation.
assert_equals(animation.playState, "finished");

await scrollSourceIntoView();

// There should still be no change to the animation.
assert_equals(animation.playState, "finished");
assert_equals(animation.currentTime, 0);
}, "Toggling trigger on starts controlling attached animation; toggling " +
"off stops");
</script>
</body>
</html>