bug#51995: 29.0.50; `string-pixel-width' depends on the current window width

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sat, 20 Nov 2021 18:42:01 -0300
> From: Brahimi Saifullah <brahimi.saifullah@gmail.com>
> Cc: 51995@debbugs.gnu.org
> 
> >Since 'window-text-pixel-size' has to deal with arbitrary buffers, it is
> >not a good idea to set X-LIMIT or Y-LIMIT to very large values.  The
> >doc-string of 'window-text-pixel-size' explicitly warns about X-LIMIT
> >that
> >
> >   Since calculating the width of long lines can take some time, it's
> >   always a good idea to make this argument as small as possible; in
> >   particular, if the buffer contains long lines that shall be truncated
> >   anyway.
> 
> I saw the warnings, but I'm unsure of their validity.
> Here are some benchmarks that I did.  Each form was run on a fresh emacs -Q.
> Apologies in advance if there is something wrong about them:
> 
> ;;; X-LIMIT nil (window width is the limit)
> (benchmark-run 100000
>   (save-window-excursion
>     (with-temp-buffer
>       (set-window-buffer nil (current-buffer))
>       (insert "foo")
                 ^^^
He mean a REALLY long line.  Like thousands of characters.