helper_displayport_estimation.html

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<title>Test for making sure that an instant scroll update on the main-thread is reflected to displayport</title>

<meta charset="utf-8">

<meta name="viewport" content="width=device-width,initial-scale=1">

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

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

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

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

<style>

html {

  overflow: scroll;

  scrollbar-width: none;

</style>

<body>

<div style="height: 50000px"></div>

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<script>

// Displayport alignment multiplier calculation; see AsyncPanZoomController::GetDisplayportAlignmentMultiplier

// https://searchfox.org/mozilla-central/rev/380b8fd795e7d96d8a5a3e6ec2b50a9f2b65854a/gfx/layers/apz/src/AsyncPanZoomController.cpp#4467-4472

function GetDisplayportAlignmentMultiplier(aBaseHeight) {

  let multiplier = 1;

  let baseHeight = aBaseHeight;

  while (baseHeight > 500) {

    baseHeight /= 2;

    multiplier *= 2;

    if (multiplier >= 8) {

      break;

  return multiplier;

async function test() {

  const resolution = await getResolution();

  const deviceScale = window.devicePixelRatio;

  // Invoke scrollToVisual to diverge the visual scroll offset from the

  // layout scroll offset.

  const utils = SpecialPowers.getDOMWindowUtils(window);

  utils.scrollToVisual(0, 1000,

                       utils.UPDATE_TYPE_MAIN_THREAD,

                       utils.SCROLL_MODE_INSTANT);

  await promiseApzFlushedRepaints();

  const initialVisualOffset = visualViewport.offsetTop;

  info(`The visualViewport.offsetTop is now ${visualViewport.offsetTop}`);

  ok(visualViewport.offsetTop > 0, `The visual viewport has scrolled`);

  info(`The visualViewport.pageTop is now ${visualViewport.pageTop}`);

  const initialScrollY = window.scrollY;

  info(`The window.scrollY is now ${window.scrollY}`);

  ok(window.scrollY > 0, `The layout viewport has scrolled`);

  is(initialScrollY + initialVisualOffset, 1000,

     "The visual scroll offset + the layout scroll offset should equal to 1000");

  // Start in a requestAnimationFrame callback so that awaiting an additional

  // requestAnimationFrame callback should result a paint.

  await promiseFrame();

  const currentTime = document.timeline.currentTime;

  // Do an instant relative scroll operation on the main-thread.

  // NOTE: Until the next paint this scroll position update will not be sent

  // to APZ.

  window.scrollBy(0, 1000);

  // Wait a frame so that a paint should have happened.

  await promiseFrame();

  // Make sure now that refresh driver's time has advanced.

  ok(document.timeline.currentTime > currentTime,

    `${document.timeline.currentTime} > ${currentTime}`);

  // Displayport margins calculation; see DisplayPortMargins::GetRelativeToLayoutViewport

  // https://searchfox.org/mozilla-central/rev/380b8fd795e7d96d8a5a3e6ec2b50a9f2b65854a/layout/base/DisplayPortUtils.cpp#85-92

  const margin = initialVisualOffset * resolution * deviceScale;

  const clientHeightInScreen = document.documentElement.clientHeight * deviceScale;

  const multiplier = GetDisplayportAlignmentMultiplier(clientHeightInScreen);

  // These calculations need to be same as the ones in GetDisplayPortFromMarginsData().

  // https://searchfox.org/mozilla-central/rev/380b8fd795e7d96d8a5a3e6ec2b50a9f2b65854a/layout/base/DisplayPortUtils.cpp#169

  const currentScrollPosition = initialScrollY + 1000;

  const currentScrollPositionInScreen = currentScrollPosition * resolution * deviceScale;

  const notAlignedDisplayportPosition = currentScrollPositionInScreen + margin;

  const displayportAlignment = 128 * multiplier;

  const alignedDisplayportPosition =

      displayportAlignment * Math.floor(notAlignedDisplayportPosition / displayportAlignment);

  let displayport = getLastContentDisplayportFor(document.documentElement.id);

  isfuzzy(displayport.y,

     (alignedDisplayportPosition - currentScrollPositionInScreen) / (resolution * deviceScale),

     1.0, // getLastContentDisplayportFor returns rounded interger values.

     "The displayport y should be reflecting the instant scroll distance");

// Scale 2.0x to diverge the visual scroll offset from the layout scroll

// offset by calling nsIDOMWindowUtils.scrollToVisual.

SpecialPowers.DOMWindowUtils.setResolutionAndScaleTo(2.0);

waitUntilApzStable()

.then(test)

.then(subtestDone, subtestFailed);

</script>

</html>