helper_checkerboard_zoom_during_load.html

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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"/>

<style>

body, html {

    margin: 0;

</style>

<body>

 <div style="height: 5000px; background-color: green"></div>

</body>

<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.

  utils.setResolutionAndScaleTo(2);

  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");

  utils.resetMobileViewportManager();

  // 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.

  utils.advanceTimeAndRefresh(0);

  assertNotCheckerboarded(utils, utils.getViewId(document.scrollingElement), `Should not see checkerboarding`);

waitUntilApzStable()

.then(test)

.then(subtestDone, subtestFailed);

</script>