[Webkit-unassigned] [Bug 104897] New: Text Autosizing: Descendants of a narrow overflow-x:scroll should use its width as an upper bound on cluster width

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=104897

           Summary: Text Autosizing: Descendants of a narrow
                    overflow-x:scroll should use its width as an upper
                    bound on cluster width
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: Unspecified
        OS/Version: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P3
         Component: Layout and Rendering
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: johnme at chromium.org
                CC: avayvod at chromium.org
            Blocks: 84186


Consider the following situation (after bug 103627 has landed):

<div style="width: 400px">
  <div style="overflow-x: scroll">
    <div style="width: 800px">
      This text should be autosized to 40px computed font size (16 * 800/320), since it's wider than the lowest common ancestor of its enclosing cluster and therefore becomes a cluster itself.<br>
      Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
    </div>
  </div>
</div>

The innermost div is 800px wide so will get a large textAutosizingMultiplier. But only 400px of the div will ever be visible at once, so the core assumption - that the user is going to zoom such that the full 800px of the div is onscreen at once - is false! Instead the innermost div should be autosized as if it were 400px wide (i.e. assume the user will zoom such that as much as possible [400px] of the div is onscreen at once).

In general, after computing the width of the lowest common ancestor of a cluster, this should be limited using the minimum of the widths of all overflow:scroll ancestors as an upper bound.

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