[Webkit-unassigned] [Bug 207089] New: Fixed elements should stay fixed with pinch-to-zoom

Sat Feb 1 01:38:12 PST 2020

https://bugs.webkit.org/show_bug.cgi?id=207089

            Bug ID: 207089
           Summary: Fixed elements should stay fixed with pinch-to-zoom
           Product: WebKit
           Version: Safari 13
          Hardware: Macintosh
                OS: macOS 10.15
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Scrolling
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: cc.glows at gmail.com

When pinch-to-zooming, `fixed` elements don't stay fixed for a period and can be scrolled, but elements positioned relative to it with `fixed` get positioned incorrectly when using `getBoundingClientRect()`. This doesn't occur when zoomed out normally (0:00 - 0:05).

When pinch to zooming as well, fixed elements can suddenly disappear after zooming in with pinch-to-zoom. Scroll down to the bottom right of the page in the repro and zoom in.

Minimal reproduction:

<!DOCTYPE html> <title>Basic Visual Test</title>

<style>
  body {
    height: 3000px;
    width: 3000px;
  }

  #reference {
    position: fixed;
    top: 150px;
    left: 150px;
    width: 200px;
    height: 200px;
    background-color: red;
    box-shadow: inset 0 0 0 1px black;
  }

  #popper {
    width: 100px;
    height: 100px;
    background-color: rebeccapurple;
    box-shadow: inset 0 0 0 1px black;
  }
</style>

<div id="reference">Reference Box</div>
<div id="popper">Popper Box</div>

<script>
  popper.style.position = 'fixed';

  function update() {
    const refRect = reference.getBoundingClientRect();
    const popRect = popper.getBoundingClientRect();

    popper.style.left = `${refRect.right}px`;
    popper.style.top = `${refRect.top + popRect.height / 2}px`;
  }

  window.addEventListener('scroll', update);
  update();
</script>

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