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

[Eli Zaretskii]

> From: Carlos Pita <carlosjosepita@gmail.com>
> Date: Mon, 14 Oct 2019 12:32:58 -0300
> Cc: Alan Third <alan@idiocy.org>, Robert Pluim <rpluim@gmail.com>, 
> 37689@debbugs.gnu.org
> 
> > 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

The image-handling code is in image.c.  The display engine in xdisp.c
uses that to perform layout calculations, and then the backends
actually display the images, e.g. look at x_draw_image_glyph_string
and its subroutines.  Fringe bitmaps use separate backend-dependent
code for the actual display, see x_draw_fringe_bitmap as one example.

> Later we can tackle "widgets" (which is the right name for them?

I suggest "images".