bug#67604: Motion problems with inline images

[Eli Zaretskii]

> From: JD Smith <jdtsmith@gmail.com>
> Date: Tue, 5 Dec 2023 23:33:42 -0500
> Cc: 67604@debbugs.gnu.org
> 
>  Not really, no.  But reproducing the problem is just a step towards
>  debugging it, so the alternative is for you to step through next-line
>  and its subroutines
> 
> I stepped through next-line and subroutines via edebug and landed via 
> line-move-visual on:
> 
>  (vertical-motion  (cons (or goal-column
>      (if (consp temporary-goal-column)
>  (car temporary-goal-column)
>        temporary-goal-column))
>  arg))
> 
> So vertical-motion is where all fingers point.

Did you verify that goal-column and temporary-goal-column have correct
values in the case where the problem happens?

>  It isn't like I'm the only
>  one who should be able to read the code and understand where it fails.
> 
> I agree with that, but unfortunately am not setup for it here and have next 
> to no familiarity with Emacs’
> C code.  I’m sorry I can’t be of more help.  But similar to how you were 
> unable to work with dvisvgm
> and other packages, I don’t have access to gdb, as it is not supported on my 
> architecture.

If someone can reproduce and debug the problem on a system other than
macOS, that would be some progress.  (If the problem is specific to
macOS, it is much less interesting, at least to me, since the display
code on macOS behaves differently in significant ways, and because
macOS is in general an idiosyncratic platform.)