percentage-mousewheel-large-scroll-offset.html

<!doctype html>
<script src="../../resources/testharness.js"></script>
<script src="../../resources/testharnessreport.js"></script>
<script src="../../resources/gesture-util.js"></script>
<style>
#scroll-div {
  width:400px; height:100px;
  overflow: auto;
  position:relative;
}
#range-div {
  width:4194410px; height: 4194410px;
  border:1px solid red;
  position:absolute;
  top: 10px;
  left: 10px;
}
</style>
<div id="scroll-div">
  <div id="range-div"></div>
</div>
<script>
  const scroller = document.querySelector("#scroll-div");
  // Scroll div to some large offset that is > 0.5*4194410
  const LARGE_SCROLL_OFFSET = 2097206;
  scroller.scrollTop = LARGE_SCROLL_OFFSET;
  scroller.scrollLeft = LARGE_SCROLL_OFFSET;
  const SCROLL_PERCENTAGE = 0.1;
  promise_test(async () => {
    // Scroll the inner scroller by the SCROLL_PERCENTAGE.
    const originalTopOffset = scroller.scrollTop;
    const originalLeftOffset = scroller.scrollLeft;

    const x = 50;
    const y = 50;
    await mouseMoveTo(x, y);

    // Use negative scroll percentages because we want to scroll up and left
    await percentScroll(-SCROLL_PERCENTAGE, -SCROLL_PERCENTAGE,
                        x, y, GestureSourceType.MOUSE_INPUT);

    function isCorrectOffset() {
      return scroller.scrollTop <=
          Math.round(originalTopOffset - scroller.clientHeight * SCROLL_PERCENTAGE);
    }
    await waitForScrollEnd(
              scroller, isCorrectOffset, true,
              "Scrolling by 10% must scroll the correct amount.");

    assert_less_than(scroller.scrollTop, originalTopOffset,
        "Must be able to scroll vertically by percentage even when at large " +
        "offset");
    assert_less_than(scroller.scrollLeft, originalLeftOffset,
        "Must be able to scroll horizontally by percentage even when at " +
        "large offset");
  }, "Can scroll by percentage at large offset");
</script>
chromium/third_party/blink/web_tests/fast/scrolling/percentage-mousewheel-large-scroll-offset.html
