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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 after zooming during page load</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">
// This function runs after page load, but simulates what might happen if
// the user does a zoom during page load. It's hard to actually do this
// during page load, because the specific behaviour depends on interleaving
// between paints and the load event which is hard to control from a test.
// So instead, we do the zoom after page load, and then trigger a MVM reset
// which simulates what happens during the pageload process.
async function test() {
var utils = SpecialPowers.getDOMWindowUtils(window);
// Make it so that the layout and visual viewports diverge. We do this by
// zooming and then moving the visual viewport.
var x = window.innerWidth / 2;
var y = window.innerHeight / 2;
utils.scrollToVisual(x, y, utils.UPDATE_TYPE_MAIN_THREAD, utils.SCROLL_MODE_INSTANT);
dump("Done scrollToVisual\n");
// Next, kick off a paint transaction to APZ, so that it sets appropriate
// displayport margins with visual/layout adjustment factors.
await promiseApzFlushedRepaints();
// Once that's done, we want to trigger the MobileViewportManager to update
// the displayport margins.
dump("Resetting MVM...\n");
// The bug is that at this point, paints end up checkerboarding because the
// MVM code to update the displayport margins doesn't preserve the layout
// adjustment factor needed.
assertNotCheckerboarded(utils, utils.getViewId(document.scrollingElement), `Should not see checkerboarding`);
.then(subtestDone, subtestFailed);