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<meta charset="utf-8">
<meta name="viewport" content="width=device-width; initial-scale=1.0">
<title>Dragging the mouse on a scrollbar for a scrollframe inside nested transforms</title>
<script type="application/javascript" src="apz_test_native_event_utils.js"></script>
<script type="application/javascript" src="apz_test_utils.js"></script>
<script src="/tests/SimpleTest/paint_listener.js"></script>
<script type="text/javascript">
async function test() {
var scrollableDiv = document.getElementById("scrollable");
let scrollPromise = new Promise(resolve => {
scrollableDiv.addEventListener("scroll", resolve, {once: true});
// Scroll down a small amount (10px). The bug in this case is that the
// scrollthumb "jumps" by an additional 40 pixels (height of the "gap" div)
// and the scrollframe scrolls by a corresponding amount. So after doing this
// drag we check the scroll position to make sure it hasn't scrolled by
// too much.
// Given the scrollable height of 2000px and scrollframe height of 400px,
// the scrollthumb should be approximately 80px tall, and dragging it 10px
// should scroll approximately 50 pixels. If the bug manifests, it will get
// dragged 50px and scroll approximately 250px.
var dragFinisher = await promiseVerticalScrollbarDrag(scrollableDiv, 10, 10);
if (!dragFinisher) {
ok(true, "No scrollbar, can't do this test");
// the events above might be stuck in APZ input queue for a bit until the
// layer is activated, so we wait here until the scroll event listener is
// triggered.
await scrollPromise;
await dragFinisher();
// Flush everything just to be safe
await promiseOnlyApzControllerFlushed();
// In this case we just want to make sure the scroll position moved from 0
// which indicates the thumb dragging worked properly.
ok(scrollableDiv.scrollTop < 100, "Scrollbar drag resulted in a scroll position of " + scrollableDiv.scrollTop);
.then(subtestDone, subtestFailed);
<div id="gap" style="min-height: 40px"></div>
<div style="height: 400px; transform: translateZ(0)">
<div style="height: 100%; opacity: 0.9; will-change: opacity">
<div id="scrollable" style="height: 100%; overflow-y: auto; transform: translateZ(0)">
<div style="min-height: 2000px">Yay text</div>