test_devicePixelRatio_with_zoom.html

Enable keyboard shortcuts

<!DOCTYPE HTML>

<html>

<head>

  <title>DevicePixelRatios with Zoom</title>

  <script src="/tests/SimpleTest/SimpleTest.js"></script>

  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css">

</head>

<body>

<div>Testing devicePixelRatio with different zoom levels</div>

<script type="application/javascript">

// We're creating a table of zooms and expected devicePixelRatio (DPR) strings.

// The values in the table are specific to the "native" DPR at zoom level 100%.

// If we don't have a table for a native DPR value, we'll trivially report

// a successful test with a note that we didn't have a table.

// For the moment, we only have a table for native DPR of 2.

let zoomsAndDPRsToTest;

const originalZoom = SpecialPowers.getFullZoom(window);

const zoom = 1;

SpecialPowers.setFullZoom(window, zoom);

const dprAtZoom1 = window.devicePixelRatio;

if (dprAtZoom1 == 1) {

  zoomsAndDPRsToTest = [

    [300, "3"],

    [250, "2.5"],

    [200, "2"],

    [167, "1.6666666666666667"],

    [150, "1.5"],

    [133, "1.3333333333333333"],

    [120, "1.2"],

    [110, "1.0909090909090908"],

    [100, "1"],

    [90,  "0.8955223880597015"],

    [80,  "0.8"],

    [67,  "0.6666666666666666"],

    [50,  "0.5"],

];

} else if (dprAtZoom1 == 2) {

  zoomsAndDPRsToTest = [

    [300, "6"],

    [250, "5"],

    [200, "4"],

    [167, "3.3333333333333335"],

    [150, "3"],

    [133, "2.608695652173913"], // there's a trailing 0 here unreported by JS

    [120, "2.4"],

    [110, "2.2222222222222223"],

    [100, "2"],

    [90,  "1.8181818181818181"],

    [80,  "1.5789473684210527"],

    [67,  "1.3333333333333333"],

    [50,  "1"],

];

if (!zoomsAndDPRsToTest.length) {

  // Need to run at least one test function to keep mochitest harness happy.

  ok(true, `No table of data for devicePixelRatio of ${dprAtZoom1} at zoom level 100%.`);

for (let i = 0; i < zoomsAndDPRsToTest.length; ++i) {

  let data = zoomsAndDPRsToTest[i];

  let zoomPercent = data[0];

  let targetDPR = data[1];

  let relativeZoom = zoom * zoomPercent / 100;

  SpecialPowers.setFullZoom(window, relativeZoom);

  // Force conversion to string for string comparison to targetDPR.

  let actualDPR = window.devicePixelRatio + "";

  is(actualDPR, targetDPR, `At ${zoomPercent}% zoom, window.devicePixelRatio is rounded correctly.`);

// Reset the zoom when the test is done.

SpecialPowers.setFullZoom(window, originalZoom);

</script>

</body>

</html>