helper_zero_delta_pan_with_prevent_default.html

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<html>

<head>

  <meta charset="utf-8">

  <meta name="viewport" content="width=device-width; initial-scale=1.0">

  <title>Test that a zero-delta pan-start event does not defeat preventDefault() on subsequent events in the same pan gesture</title>

  <script src="apz_test_utils.js"></script>

  <script src="apz_test_native_event_utils.js"></script>

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

  <style>

    #spacer {

      height: 500vh;

  </style>

</head>

<body>

  <div id="spacer"></div>

</body>

<script>

async function test() {

  const preventDefault = e => e.preventDefault();

  window.addEventListener("wheel", preventDefault, { passive: false });

  // Start in the middle of the page so the test does not depend on the

  // scroll direction of the synthesized pan (which is reversed on Linux,

  // see bug 1889039).

  window.scrollTo(0, window.innerHeight * 2);

  await promiseApzFlushedRepaints();

  const startY = window.scrollY;

  ok(startY > 0, "Should start scrolled down");

  // The zero-delta pan-start does not result in a DOM wheel event, so the

  // listener cannot prevent it. It must not cause APZ to treat the block as

  // not prevented, and scroll in response to the next event before content

  // has had a chance to prevent that.

  const wheelPromise = promiseOneEvent(window, "wheel");

  await NativePanHandler.promiseNativePanEvent(

    window, 100, 100, 0, 0, NativePanHandler.beginPhase);

  await NativePanHandler.promiseNativePanEvent(

    window, 100, 100, 0, NativePanHandler.delta, NativePanHandler.updatePhase);

  await wheelPromise;

  // Wait for the content response for the pan-update to be sent, and for APZ

  // to process it.

  await promiseFrame();

  await promiseApzFlushedRepaints();

  is(window.scrollY, startY, "Should not have scrolled");

  await NativePanHandler.promiseNativePanEvent(

    window, 100, 100, 0, 0, NativePanHandler.endPhase);

  // Check that the same gesture does scroll without the listener, so that the

  // above check is not passing for some unrelated reason.

  window.removeEventListener("wheel", preventDefault, { passive: false });

  window.scrollTo(0, startY);

  await promiseApzFlushedRepaints();

  const scrollPromise = promiseOneEvent(window, "scroll");

  await NativePanHandler.promiseNativePanEvent(

    window, 100, 100, 0, 0, NativePanHandler.beginPhase);

  await NativePanHandler.promiseNativePanEvent(

    window, 100, 100, 0, NativePanHandler.delta, NativePanHandler.updatePhase);

  await scrollPromise;

  isnot(window.scrollY, startY, "Should have scrolled without the listener");

  await NativePanHandler.promiseNativePanEvent(

    window, 100, 100, 0, 0, NativePanHandler.endPhase);

waitUntilApzStable()

.then(test)

.then(subtestDone, subtestFailed);

</script>

</html>