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<!DOCTYPE html>
<link rel="help" href="https://drafts.csswg.org/css-scroll-snap-1/#scroll-snap-type" />
<title>Mouse-wheel scroll snapping speed</title>
<meta name="assert"
content="Test passes if mousewheel snaps without pausing">
<style>
#scroller {
scroll-snap-type: block mandatory;
overflow: scroll;
height: 400px;
width: 400px
}
#space {
width: 200px;
height: 4000px;
}
.box {
scroll-snap-align: start;
background: blue;
margin-bottom: 10px;
width: 100px;
height: 100px;
}
</style>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/resources/testdriver.js"></script>
<script src="/resources/testdriver-vendor.js"></script>
<script src="/resources/testdriver-actions.js"></script>
<script src="../support/common.js"></script>
<div id="scroller">
<div class="box"></div>
<div class="box"></div>
<div id="space"></div>
</div>
<script>
promise_test(async t => {
const scroller = document.getElementById("scroller");
scroller.scrollTo(0, 0);
assert_equals(scroller.scrollTop, 0, "verify test pre-condition");
const scrollTop = () => {
return scroller.scrollTop;
};
const scrollPromise = waitForScrollEvent(scroller);
const wheelPromise = waitForWheelEvent(scroller);
const actions = new test_driver.Actions()
.scroll(50, 50, 0, 50, {origin: scroller, duration: 100});
await actions.send();
await wheelPromise;
await scrollPromise;
let scrollEndTime;
let snapEndTime;
// Detect first pause in scrolling.
const scrollStabilizedPromise =
waitForAnimationEnd(scrollTop).then((timestamp) => {
scrollEndTime = timestamp;
});
const snapEndPromise =
waitForScrollTo(scroller, () => {
return scroller.scrollTop;
}, 110).then((evt) => {
snapEndTime = evt.timestamp;
});
await Promise.all([scrollStabilizedPromise, snapEndPromise]);
assert_equals(scroller.scrollTop, 110,
'Failed to advance to next snap target');
assert_true(snapEndTime < scrollEndTime,
'Detected pause in scrolling before reaching snap target');
}, "Wheel-scroll triggers snap to target position immediately.");
</script>
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