test_hit_test_no_display_list_build.html

Enable keyboard shortcuts

<!DOCTYPE HTML>

<html>

<head>

<meta charset="utf-8">

<title>Test that hit testing does not mark a frame's display list as built (bug 2043935)</title>

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

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

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

<style>

  #target { width: 100px; height: 100px; background: green; }

</style>

</head>

<body>

<div id="target"></div>

<script>

SimpleTest.waitForExplicitFinish();

const utils = SpecialPowers.getDOMWindowUtils(window);

async function runTest() {

  const docElement = document.documentElement;

  const target = document.getElementById("target");

  // Positive control: the initial paint builds the document's display list, so

  // the flag must be set. This also clears it for the measurement below, and

  // guards against the fix simply never recording the build.

  await promiseAllPaintsDone(null, /* flush = */ true);

  ok(utils.checkAndClearDisplayListState(docElement),

     "Painting should mark the document element's display list as built");

  // elementFromPoint performs main-thread hit testing, which builds a display

  // list in EventDelivery mode over the root frame. Hit testing must not mark

  // the frame's display list as built; only painting display list builds are

  // recorded (see nsDisplayListBuilder::IsForPainting). The whole sequence runs

  // synchronously, so no paint can interleave between the clear above and the

  // check below.

  const rect = target.getBoundingClientRect();

  const x = Math.floor(rect.left + rect.width / 2);

  const y = Math.floor(rect.top + rect.height / 2);

  for (let i = 0; i < 5; i++) {

    is(document.elementFromPoint(x, y), target,

       "elementFromPoint should hit the target (so a hit test really happened)");

  is(utils.checkAndClearDisplayListState(docElement), false,

     "Hit testing should not mark the document element's display list as built");

  SimpleTest.finish();

SimpleTest.waitForFocus(runTest);

</script>

</body>

</html>