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| 1 | +<!DOCTYPE html> |
| 2 | +<meta name="viewport" content="width=device-width,initial-scale=1"> |
| 3 | +<link rel="help" href="https://drafts.csswg.org/css-scroll-snap/#re-snap" /> |
| 4 | +<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1978946"> |
| 5 | +<script src="/resources/testharness.js"></script> |
| 6 | +<script src="/resources/testharnessreport.js"></script> |
| 7 | +<style> |
| 8 | +#scroller { |
| 9 | + overflow-y: auto; |
| 10 | + scroll-snap-type: y mandatory; |
| 11 | + width: 100vw; |
| 12 | + height: calc(100svh - 80px); |
| 13 | +} |
| 14 | +.child { |
| 15 | + scroll-snap-align: start; |
| 16 | + scroll-snap-stop: always; |
| 17 | + width: 100%; |
| 18 | + height: calc(100svh - 80px); |
| 19 | + font-size: 30px; |
| 20 | +} |
| 21 | +.child:last-child { |
| 22 | + background-image: linear-gradient(to right, black 1px, transparent 1px), |
| 23 | + linear-gradient(to bottom, black 1px, transparent 1px); |
| 24 | + background-size: 64px 64px; |
| 25 | + height: 200%; |
| 26 | +} |
| 27 | +</style> |
| 28 | +<div id="scroller"> |
| 29 | + <div class="child">1</div> |
| 30 | + <div class="child">2</div> |
| 31 | +</div> |
| 32 | +<script> |
| 33 | +promise_test(async () => { |
| 34 | + assert_equals(scroller.scrollTop, 0); |
| 35 | + |
| 36 | + const scrollendPromise = new Promise(resolve => { |
| 37 | + scroller.addEventListener("scrollend", resolve); |
| 38 | + }); |
| 39 | + |
| 40 | + const expectedPosition = |
| 41 | + scroller.children[0].getBoundingClientRect().height + 100; |
| 42 | + // Try to scroll downward, it will snap to a position inside |
| 43 | + // the second child. |
| 44 | + scroller.scrollTo(0, expectedPosition); |
| 45 | + await scrollendPromise; |
| 46 | + |
| 47 | + assert_equals(scroller.scrollTop, expectedPosition, |
| 48 | + "The scroll position is the expected one"); |
| 49 | + |
| 50 | + // Change the second child width, it will re-evaluate the snap position. |
| 51 | + scroller.querySelector(":last-child").style.width = "99%"; |
| 52 | + |
| 53 | + // Give a chance to scroll if it happens. |
| 54 | + await new Promise(resolve => { |
| 55 | + requestAnimationFrame(() => requestAnimationFrame(resolve)); |
| 56 | + }); |
| 57 | + |
| 58 | + assert_equals(scroller.scrollTop, expectedPosition, |
| 59 | + "Should stay at the last snap point"); |
| 60 | +}, "Keep the same snap position on overflowing-snap-area when re-snapping"); |
| 61 | +</script> |
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