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<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Skip re-snapping during scrollbar dragging</title>
<script src="apz_test_utils.js"></script>
<script src="apz_test_native_event_utils.js"></script>
<script src="/tests/SimpleTest/paint_listener.js"></script>
<style>
body {
margin: 0;
}
div {
position: absolute;
}
#scroller {
width: 100%;
height: 500px;
overflow-y: scroll;
scroll-snap-type: y mandatory;
}
.child {
width: 100%;
height: 100px;
background-color: blue;
scroll-snap-align: start;
}
</style>
</head>
<body>
<div id="scroller">
<div class="child" style="top: 0px;"></div>
<div id="spacer" style="width: 100%; height: 2000px;"></div>
</div>
<script type="application/javascript">
async function test() {
is(scroller.scrollTop, 0, "The initial snap point is at 0px");
// Move onto the scroll thumb for the scroller element.
let w = {}, h = {};
SpecialPowers.DOMWindowUtils.getScrollbarSizes(scroller, w, h);
if (w.value == 0) {
ok(true, "No scrollbar, can't do this test");
return;
}
const x = scroller.clientWidth + w.value / 2;
await promiseNativeMouseEventWithAPZ({
target: scroller,
offsetX: x,
offsetY: w.value + 5,
type: "mousemove"});
// Start dragging the thumb.
await promiseNativeMouseEventWithAPZ({
target: scroller,
offsetX: x,
offsetY: w.value + 5,
type: "mousedown",
});
// Move down the thumb to scroll.
let scrollEventPromise = waitForScrollEvent(scroller);
await promiseNativeMouseEventWithAPZ({
target: scroller,
offsetX: x,
offsetY: w.value + 10,
type: "mousemove"});
await scrollEventPromise;
ok(scroller.scrollTop > 0, "Dragging the scroll thumb should scroll");
// Expand the scrollable region during the dragging.
spacer.style.height = "2200px";
isnot(scroller.scrollTop, 0, "Do not re-snap to the original 0px");
let previousScrollPosition = scroller.scrollTop;
scrollEventPromise = waitForScrollEvent(scroller);
// Release the mouse button, it will trigger snapping.
await promiseNativeMouseEventWithAPZ({
target: scroller,
offsetX: x,
offsetY: 10,
type: "mouseup"});
await scrollEventPromise;
// Make sure the new scroll positions have reached to the main-thread.
await promiseApzFlushedRepaints();
// There's no good way to tell whether the snapping has finished, has
// reached to the snap destination, so we just check whether the current
// scroll position is a bit scrolled back toward the snap destination.
ok(scroller.scrollTop < previousScrollPosition,
"Releasing the mouse button should trigger snapping toward 0px");
}
waitUntilApzStable()
.then(test)
.then(subtestDone, subtestFailed);
</script>
</body>
</html>
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