<!DOCTYPE html>
<title>
Updating the snap alignment of a snap container's content should make the snap
container resnap accordingly.
</title>
<link rel="help" href="https://drafts.csswg.org/css-scroll-snap/#re-snap" />
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
div {
position: absolute;
margin: 0;
}
#scroller {
height: 200px;
width: 200px;
overflow: hidden;
scroll-snap-type: both mandatory;
}
#initial-target {
width: 300px;
height: 300px;
top: 100px;
left: 100px;
background-color: green;
scroll-snap-align: start;
}
#other-target {
width: 300px;
height: 300px;
top: 300px;
left: 300px;
background-color: red;
scroll-snap-align: start;
}
.area {
width: 2000px;
height: 2000px;
}
.snap-area {
scroll-snap-align: start !important;
}
</style>
<div id="scroller">
<div class="area"></div>
<div id="initial-target"></div>
<div id="other-target"></div>
</div>
<script>
const initial_target = document.getElementById("initial-target");
const other_target = document.getElementById("other-target");
const scroller = document.getElementById("scroller");
function cleanup() {
initial_target.style.setProperty("scroll-snap-align", "start");
other_target.style.setProperty("scroll-snap-align", "start");
initial_target.removeAttribute("class");
}
test(t => {
t.add_cleanup(cleanup);
scroller.scrollTo(0,0);
assert_equals(scroller.scrollTop, 100);
assert_equals(scroller.scrollLeft, 100);
initial_target.style.setProperty("scroll-snap-align", "end");
// scroller maintains scroll position which is still valid as the target's
// snap area covers the snap port.
assert_equals(scroller.scrollTop, 100);
assert_equals(scroller.scrollLeft, 100);
}, "Changing a large target's snap alignment shouldn't make the scroller" +
" resnap if the scroller is already in a valid snap position.");
// Similar to above test case except targets are too small to cover snap port,
// so scroller must snap in response to change in scroll-snap-align.
test(t => {
t.add_cleanup(cleanup);
const initial_target_height = initial_target.offsetHeight;
const initial_target_width = initial_target.offsetWidth;
const other_target_height = initial_target.offsetHeight;
const other_target_width = initial_target.offsetWidth;
t.add_cleanup(() => {
initial_target.style.setProperty("height", `${initial_target_height}px`);
initial_target.style.setProperty("width", `${initial_target_width}px`);
other_target.style.setProperty("height", `${other_target_height}px`);
other_target.style.setProperty("width", `${other_target_width}px`);
})
scroller.scrollTo(0,0);
assert_equals(scroller.scrollTop, 100);
assert_equals(scroller.scrollLeft, 100);
initial_target.style.setProperty("height", `${scroller.clientHeight * 2/3 }px`);
initial_target.style.setProperty("width", `${scroller.clientWidth * 2/3 }px`);
other_target.style.setProperty("height", `${scroller.clientHeight * 2/3 }px`);
other_target.style.setProperty("width", `${scroller.clientWidth * 2/3 }px`);
// scroll (and snap) to top left of other target.
scroller.scrollTo(other_target.offsetTop,
other_target.offsetLeft);
assert_equals(scroller.scrollTop, other_target.offsetTop,);
assert_equals(scroller.scrollLeft, other_target.offsetLeft);
other_target.style.setProperty("scroll-snap-align", "end");
// should be scrolled so as to align scroller's bottom-right with
// other_target's bottom-right.
assert_equals(scroller.scrollTop,
other_target.offsetTop + other_target.offsetHeight - scroller.clientHeight);
assert_equals(scroller.scrollLeft,
other_target.offsetLeft + other_target.offsetWidth - scroller.clientWidth);
}, "Changing the current (non-covering) target's snap alignment should make " +
"the scroller snap according to the new alignment.");
</script>
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