bug#67533: SVG images confound position pixel measurements

[Eli Zaretskii]

> From: JD Smith <jdtsmith@gmail.com>
> Date: Fri, 1 Dec 2023 10:21:19 -0500
> Cc: Manuel Giraud <manuel@ledu-giraud.fr>,
>  67533@debbugs.gnu.org
> 
> 
> > Btw, I wonder what you and JD expect from the (cons (point) -1)
> > argument.  The doc string says:
> > 
> >  If FROM is a cons, its car specifies a buffer position, and its cdr
> >  specifies the vertical offset in pixels from that position to the
> >  first screen line to be measured.
> > 
> > What is the meaning of negative offset from the first line of the
> > buffer? there's no screen line at that offset, so what do you expect
> > that to do?  Or what am I missing?
> 
> In that case I would expect zero pixel height is returned.

Why zero?  Why not consider that undefined behavior?

> I’ll work up a simpler reproducer in non-truncated and/or visual-line-mode.

Thanks.