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<!DOCTYPE html>
<html>
<body>
<style>
#space {
height: 300vh;
width: 300vw;
position: absolute;
}
#scroller {
overflow-y: scroll;
scroll-snap-type: y mandatory;
width: 450px;
height: 450px;
border: solid 1px black;
position: relative;
}
.box {
height: 200px;
width: 200px;
position: absolute;
background-color: green;
scroll-snap-align: start;
}
.box:target {
background-color: red;
}
.toprow { top: 0px; }
.midrow { top: 210px; }
.bottomrow { top: 420px; }
.leftcol { left: 0px; }
.midcol { left: 210px; }
.rightcol { left: 420px; }
</style>
<div id="scroller">
<div id="space"></div>
<div class="leftcol toprow box" id="box1"></div>
<div class="midcol toprow box" id="box2"></div>
<div class="rightcol toprow box" id="box3"></div>
<div class="leftcol midrow box" id="box4"></div>
<div class="midcol midrow box" id="box5"></div>
<div class="rightcol midrow box" id="box6"></div>
<div class="leftcol bottomrow box" id="box7"></div>
<div class="midcol bottomrow box" id="box8"></div>
<div class="rightcol bottomrow box" id="box9"></div>
</div>
<script>
// This test sets up a 3x3 grid within scroller:
// -------------------------
// | Box 1 | Box 2 | Box 3 |
// ------------------------
// | Box 4 | Box 5 | Box 6 |
// -------------------------
// | Box 7 | Box 8 | Box 9 |
// -------------------------
// This function just gets the numbers beside |box_number| on each row.
// E.g. 4: 4%3 = 1; so the numbers we want are 5 (4+1) and 6 (4+2).
function getAlignedNumbers(n) {
n = parseInt(n);
const mod_3 = n % 3;
if (mod_3 == 1) {
return [n + 1, n + 2];
} else if (mod_3 == 2) {
return [n - 1, n + 1];
}
return [n - 1, n - 2];
}
function stashResult(key, result) {
fetch(`/css/css-scroll-snap/snap-after-relayout` +
`/multiple-aligned-targets/stash.py?key=${key}`, {
method: "POST",
body: result
}).then(() => {
window.close();
});
}
function assert_equals(v1, v2) {
if (v1 != v2) {
throw new Error(`Expected equality of v1(${v1}) and v2(${v2}).`);
}
}
async function record() {
let key = (new URL(document.location)).searchParams.get("key");
try {
// Get the id of that targeted element.
const target_id = location.hash.substring(1);
const box_number = target_id.substring(3);
// Get the elements aligned with the targeted element.
const target = document.getElementById(target_id);
if (target == null) {
throw new Error("Null hash fragment target.");
}
let [aligned_number_1, aligned_number_2] =
getAlignedNumbers(box_number);
const aligned_box_1 = document.getElementById(`box${aligned_number_1}`);
const aligned_box_2 = document.getElementById(`box${aligned_number_2}`);
// Make sure all the boxes are equally aligned.
assert_equals(aligned_box_1.offsetTop, target.offsetTop);
assert_equals(aligned_box_1.offsetTop, aligned_box_2.offsetTop);
// Scroll to the aligned boxes if necessary.
if (scroller.scrollTop != target.offsetTop) {
const scrollend_promise = new Promise((res) => {
scroller.addEventListener(res);
});
scroller.scrollTop = target.offsetTop;
await scrollend_promise;
}
// Save target's original top and move it down by 100px;
const original_top = getComputedStyle(target).top;
target.style.top = `${target.offsetTop + 100}px`;
// Assert that scroller followed target as it moved down.
assert_equals(scroller.scrollTop, target.offsetTop);
// Cleanup: undo style change.
target.style.top = `${original_top}px`;
// Stash result.
stashResult(key, "PASS");
} catch (error) {
stashResult(key, error.message);
}
}
window.onload = () => {
window.requestAnimationFrame(function () {
window.requestAnimationFrame(record);
})
}
</script>
</body>
</html>
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