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<!DOCTYPE html>
<html lang="en"><head>
<meta http-equiv="content-type" content="text/html; charset=UTF-8"><meta charset="utf-8">
<title>Testcase for checkerboarding with displayport multipliers dropped to zero</title>
<script type="application/javascript" src="apz_test_utils.js"></script>
<script src="/tests/SimpleTest/paint_listener.js"></script>
<meta name="viewport" content="width=device-width"/>
body, html {
margin: 0;
<div style="height: 5000px; background-color: green"></div>
<script type="application/javascript">
async function test() {
var utils = SpecialPowers.getDOMWindowUtils(window);
var scrollerId = utils.getViewId(document.scrollingElement);
// Zoom in a bunch
const scale = 3.0;
// And now we scroll the visual viewport to cover the range it has inside
// the layout viewport, plus a bit more so that we also cover the boundary
// case where the layout viewport has to move.
// At each scroll position, we make sure there's no checkerboarding.
// We advance the scroll position on each axis by 43 CSS pixels at a time,
// because 43 is a non-power-of-two/prime number and should give us reasonable
// coverage of different displayport tile alignment values. Making the
// increment too small increases runtime and too large might miss some
// alignment values so this seems like a good number.
async function scrollAndCheck(x, y) {
dump(`Scrolling visual viewport to ${x}, ${y}\n`);
utils.scrollToVisual(x, y, utils.UPDATE_TYPE_MAIN_THREAD, utils.SCROLL_MODE_INSTANT);
await promiseApzFlushedRepaints();
assertNotCheckerboarded(utils, scrollerId, `At ${x}, ${y}`);
let vv_scrollable_x = window.innerWidth - (window.innerWidth / scale);
for (var x = 0; x < vv_scrollable_x + 100; x += 43) {
await scrollAndCheck(x, 0);
ok(window.scrollX == 0, "Layout viewport couldn't move on the x-axis, page not scrollable that way");
let vv_scrollable_y = window.innerHeight - (window.innerHeight / scale);
for (var y = 0; y < vv_scrollable_y + 100; y += 43) {
await scrollAndCheck(0, y);
ok(window.scrollY > 0, `Layout viewport moved down to ${window.scrollY} on the y-axis`);
.then(subtestDone, subtestFailed)