bug#41513: `compute-motion' can miscount buffer positions in the presence of 'before-string/'after-string overlays

[Eli Zaretskii]

> From: Stephen Bach <sjbach@sjbach.com>
> Date: Sun, 24 May 2020 15:55:09 -0400
> Cc: 41513@debbugs.gnu.org
> 
> > There are other functions that can do the same job.  If you describe
> > what you need to do, I could try suggesting some alternatives that
> > will work.
> 
> Thanks Eli. Specifically, I'm measuring the jagged contour of a buffer's
> layout within a particular window, i.e. relating the final column of
> each visual row (as displayed within the window) to concrete buffer
> positions. This is notionally straightforward but complicated in
> practice, as you will know -- e.g. line continuation/truncation,
> `word-wrap', `visual-line-mode', `adaptive-wrap-prefix-mode',
> multi-columnar glyphs. Text properties or overlays using 'display, and
> so on.

Please tell more.  What exactly would you like to measure?  Is it the
width of each screen line? or just the maximum width of the longest
line among those shown in the window? or something else?