bug#67533: SVG images confound position pixel measurements

[Eli Zaretskii]

> From: JD Smith <jdtsmith@gmail.com>
> Date: Fri, 1 Dec 2023 10:45:00 -0500
> Cc: Manuel Giraud <manuel@ledu-giraud.fr>,
>  67533@debbugs.gnu.org
> 
> 
> 
> > On Dec 1, 2023, at 10:36 AM, Eli Zaretskii <eliz@gnu.org> wrote:
> > 
> >> 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?
> 
> Depends on what the natural height on a non-existent line is.  Zero makes 
> sense to me.  But I suppose returning height=nil or something else to 
> indicate “I gave up” would also be reasonable. 

A non-existent line can have any height, including an infinite one.
Since that line doesn't exist, any assertion about it cannot be
disproved.