bug#37689: Fringe pixmaps, widgets, etc. look ridiculously tiny in hidpi screen

[Carlos Pita]

> > factor, thus solving points 1, 2 and 3 above.
>
> Sorry, problem 1 is still unsolved by the proposed approach, not
> without extending redisplay_interface.

Also, the scaling factor should probably be exposed to frame.c, since
it sets a default width of 8 that assumes a standard dpi monitor:

gui_set_left/right_fringe (struct frame *f, Lisp_Object new_value,
Lisp_Object old_value)
  ...
  new_width = (RANGED_FIXNUMP (-INT_MAX, new_value, INT_MAX)
       ? eabs (XFIXNUM (new_value)) : 8);

I've reached a point from where I'm unable to continue ahead on my
own, except for writing a private patch targeting my specific
resolution and backend. I would like to contribute but I see no way
without extending the interface and that's far beyond than what I can
decide.