bug#69602: 29.1; Image :map should adjust with :scale and :rotation

[Eli Zaretskii]

> From: Joseph Turner <joseph@breatheoutbreathe.in>
> Cc: 69602@debbugs.gnu.org, stephen.berman@gmx.net, juri@linkov.net
> Date: Wed, 06 Mar 2024 23:14:21 -0800
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> > The ELisp manual says about :map:
> >
> >      Note that the map's coordinates should reflect the displayed image
> >      after all transforms have been done (rotation, scaling and so on),
> >      and also note that Emacs (by default) performs auto-scaling of
> >      images, so to make things match up, you should either specify
> >      ‘:scale 1.0’ when creating the image, or use the result of
> >      ‘image-compute-scaling-factor’ to compute the elements of the map.
> >
> > Can this technique help?
> 
> Thank you for your help!
> 
> When the user runs `image-increase-size', where should third-party code
> recompute :map to fit the new image scale?
> 
> There's no `image-after-change-size-hook' nor `image-after-rotate-hook'.

I think the idea is to define the value of :map such that it runs
image-compute-scaling-factor as part of computing the coordinates of
the map.