bug#67533: SVG images confound position pixel measurements

[Eli Zaretskii <eliz@gnu.org>]

> From: Manuel Giraud <manuel@ledu-giraud.fr>
> Cc: JD Smith <jdtsmith@gmail.com>,  67533@debbugs.gnu.org
> Date: Fri, 01 Dec 2023 15:40:59 +0100
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > Does the patch below fix the issue?  (It should fix the recipe you
> > posted, but you hinted that this is just the simplest way of seeing a
> > more general problem, so I wonder whether that more general problem is
> > also fixed.)
> 
> Hi,
> 
> I have applied your patch to master and here are the results I get with
> the recipe at the end of this message:
> 
> With a not large enough window:
>   FIRST LINE: (925 24 1); ABOVE IMAGE: (925 24 119)
> 
> With a large enough window (i.e., that can display the whole first
> line):
>   FIRST LINE: (1053 24 1); ABOVE IMAGE: (1062 24 119)

If you think these results still show a problem, please elaborate.
Since you did this on your system, with your fonts and frame
dimensions, I cannot know whether the numbers are correct or not.

The patch I posted is supposed to fix only one issue: the fact that
the Y-dimension of the line above the image was shown as zero.  AFAIU,
it is indeed not zero in the output you show above.

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?