uncomposite-and-composite-scroll.html

<!DOCTYPE html>
<script src='../../resources/testharness.js'></script>
<script src='../../resources/testharnessreport.js'></script>
<script src='../../resources/gesture-util.js'></script>
<style type="text/css">
    #outer {
      background: #fff;
      position: absolute
    }

    #inner {
      max-height: 300px;
      max-width: 116px;
      overflow-y: auto;
      will-change: transform;
    }

    /* Custom scrollbar so they're updated on the main thread only */
    ::-webkit-scrollbar {
      height: 16px;
      width: 16px
    }

    ::-webkit-scrollbar-thumb {
      background-color: grey;
    }

    /* An interesting background so we can tell we're scrolling */
    #spacer {
      height: 3000px;
      width: 100px;
      background-color: #FFF;
      background-size: 50px 50px;
      background-position: 0 0, 25px 25px;
      background-image: linear-gradient(45deg, black 25%, transparent 25%, transparent 75%, black 75%, black),
                        linear-gradient(45deg, black 25%, transparent 25%, transparent 75%, black 75%, black);

    }
</style>
<div id="outer">
   <div id="inner">
      <div id="spacer"></div>
   </div>
  <p>
    Scroll the above box with wheel or touch. If the scrollbar moves with the
    scroll the test passes.
  </p>
</div>
 <script>
    addEventListener('load', async () => {
      let scroller = document.getElementById('inner');

      // Add style that will cause the PaintLayer and associated compositing
      // layers to get deleted.
      scroller.style.overflowY = 'visible';
      scroller.style.willChange = 'auto';

      // Force a style and layout recalc.
      scroller.offsetHeight;

      // Remove the style so that a new PaintLayer and compositing layers are
      // re-added.
      scroller.style.willChange = '';
      scroller.style.overflowY = '';

      await waitForCompositorCommit();

      promise_test(async () => {
        const delta = 1000;
        const location = { x: 50, y: 50 };
        await smoothScroll(delta,
                           location.x,
                           location.y,
                           GestureSourceType.TOUCH_INPUT,
                           'down',
                           SPEED_INSTANT);

        // Will throw exception if window.scrollY not greater than 0.
        assert_greater_than(scroller.scrollTop, 0,
                            "Scroller should be scrolled.");
      }, 'Tests that composited scrolling works after de-and-re-compositing scroller.');


    });
 </script>
chromium/third_party/blink/web_tests/fast/scrolling/uncomposite-and-composite-scroll.html
