test_scrolling_repaints.html

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<!DOCTYPE HTML>

<html>

<head>

  <title>Test that we don't get unnecessary repaints due to subpixel shifts</title>

  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>

  <script src="chrome://mochikit/content/tests/SimpleTest/paint_listener.js"></script>

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

</head>

<!-- Need a timeout here to allow paint unsuppression before we start the test -->

<body onload="setTimeout(startTest,0)">

<div id="t" style="width:400px; height:100px; background:yellow; overflow:hidden">

  <div style="height:40px;"></div>

  <div id="e" style="height:30px; background:lime"></div>

  <div style="height:60.4px; background:pink"></div>

</div>

<pre id="test">

<script type="application/javascript">

SimpleTest.waitForExplicitFinish();

var t = document.getElementById("t");

var e = document.getElementById("e");

var utils = window.windowUtils;

function startTest() {

  // Do a scroll to ensure we trigger activity heuristics.

  waitForAllPaintsFlushed(function () {

    t.scrollTop = 5;

	// Scroll down as far as we can, to put our rendering layer at a subpixel offset within the layer

    waitForAllPaintsFlushed(function () {

      t.scrollTop = 1000;

      waitForAllPaintsFlushed(function () {

        // Clear paint state now and scroll again.

        utils.checkAndClearPaintedState(e);

		// scroll up a little bit. This should not cause anything to be repainted.

        t.scrollTop = t.scrollTop - 10;

        waitForAllPaintsFlushed(function () {

          var painted = utils.checkAndClearPaintedState(e);

          is(painted, false, "Fully-visible scrolled element should not have been painted");

          SimpleTest.finish();

});

});

});

});

</script>

</pre>

</body>

</html>