Source code

Revision control

Copy as Markdown

Other Tools

<meta charset="utf-8">
<meta name="viewport" content="width=device-width; initial-scale=1.0">
<title>Test for bug 1719913</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 subframe = document.getElementById("scroller");
let scrollPromise = new Promise(resolve => {
subframe.addEventListener("scroll", resolve, {once: true});
// Scroll down a small amount (5px). The bug in this case is that the
// scrollthumb "jumps" further down the scroll track because with the bug,
// incorrect location of a transform in the WebRender scroll nodes results
// in a miscalculation of the scroll position corresponding to a mouse event
// position during dragging.
var dragFinisher = await promiseVerticalScrollbarDrag(subframe, 5, 5);
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();
// The expected scroll position from the 5px of dragging, based on local
// testing, is 49px. With the bug, it's 1038px. We check that it's < 100
// which should rule out the bug while allowing for minor variations in
// scrollbar sizing etc.
ok(subframe.scrollTop < 100, "Scrollbar drag resulted in a scroll position of " + subframe.scrollTop);
.then(subtestDone, subtestFailed);
.columns {
position: absolute;
top: 0;
right: 0;
bottom: 0;
left: 0;
overflow: auto;
.column {
position: relative;
width: 50%;
height: 500px;
.header {
height: 100px;
.scroller {
overflow: auto;
will-change: transform;
height: 100%;
.content {
height: 5000px;
width: 100%;
background: linear-gradient(green, blue);
<div class="columns">
<div class="column">
<div class="header"></div>
<div class="scroller" id="scroller">
<div class="content"></div>
<div class="column"></div>