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

[Carlos Pita <carlosjosepita@gmail.com>]

> What you call "widgets" are images.  Fringes are also images, but
their format is fixed: they are always bitmaps.

> I think we covered all that, what is left is coding.  Right?

Well, I know they're images, I even known which images they are, I
just haven't spotted the place where they're actually dealt with in
the low level code and I was surprised that, being images, changes to
x_cr_render_image weren't having any effect on them (with the cairo
backend enabled, of course). To add to my confusion there are the
aforementioned differences between 26.3 and 27 in this regard. The
question of which code is dealing with these images (as opposed to
fringe bitmaps) was indeed left unanswered but, nevermind, I'll keep
looking for it myself. Any additional hint would be much appreciated,
though.

For the time being I will focus on fringe bitmaps and work under this
assumption (which I'm not sure is that mild as you seem to suggest):

> I don't think individual backends do any scaling, but if some do, it
> should be easy to disable the scaling in our code for those backends.

Later we can tackle "widgets" (which is the right name for them? They
are indeed defined in widget.el and wid-edit.el AFAICS).

Best regards
--
Carlos