test_pixel_lengths.html

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<!DOCTYPE HTML>

<html>

<head>

  <title>Test that pixel lengths don't change based on DPI</title>

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

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

</head>

<body>

<div id="display">

<div id="pt" style="width:90pt; height:90pt; background:lime;">pt</div>

<div id="pc" style="width:5pc; height:5pc; background:yellow;">pc</div>

<div id="mm" style="width:25.4mm; height:25.4mm; background:orange;">mm</div>

<div id="cm" style="width:2.54cm; height:2.54cm; background:purple;">cm</div>

<div id="in" style="width:1in; height:1in; background:magenta;">in</div>

<div id="q" style="width:101.6q; height:101.6q; background:blue;">q</div>

</div>

<pre id="test">

<script class="testbody" type="text/javascript">

var oldDPI = SpecialPowers.getIntPref("layout.css.dpi");

var dpi = oldDPI;

function check(id, val) {

  var e = document.getElementById(id);

  is(Math.round(e.getBoundingClientRect().width), Math.round(val),

     "Checking width in " + id + " at " + dpi + " DPI");

  is(Math.round(e.getBoundingClientRect().height), Math.round(val),

     "Checking height in " + id + " at " + dpi + " DPI");

function checkPixelRelativeUnits() {

  check("pt", 120);

  check("pc", 80);

  check("mm", 96);

  check("cm", 96);

  check("in", 96);

  check("q", 96);

checkPixelRelativeUnits();

SimpleTest.waitForExplicitFinish();

SpecialPowers.pushPrefEnv({'set': [['layout.css.dpi', dpi=96]]}, test1);

function test1() {

  checkPixelRelativeUnits();

  SpecialPowers.pushPrefEnv({'set': [['layout.css.dpi', dpi=192]]}, test2);

function test2() {

  checkPixelRelativeUnits();

  SimpleTest.finish();

</script>

</pre>

</body>

</html>