Implementing image support for kitty terminal

[Jose Antonio Ortega Ruiz <jao@gnu.org>]

Hi,

The kitty terminal emulator (which runs under X11 and wayland) offers a
simple protocol for displaying images, fully described at
<https://sw.kovidgoyal.net/kitty/graphics-protocol/>.  

In a nutshell, it accepts an escape sequence that make it enter "graphic
mode", followed by either encoded image data or a path to an image file
or a shared memory location to display.  Among several other niceties,
the protocol allows drawing to rectangles specified in cell units. As a
simple example, the sequence:

   <ESC>_Gf=100,t=f,c=50,r=100;<encoded /path/to/file.png><ESC>\

would make kitty draw the image in file.png rescaling it to 50 columns
and 100 rows.  By default, the current cursor position is used, but it's
also possible to specify pixel offsets and sizes.

At first sight, it looks as if adding support for this protocol to
emacs's tty terminal (when kitty, or the capability (it seems other
terminals support the same protocol) is detected) shouldn't be too
complex, and with that, perhaps, provide direct support for the
elisp-level image- API for these terminals (so that, for instance,
doc-view or pdf-tools or displaying images in eww buffers would work out
of the box).  Am i wrong?

On a personal note, if that were possible it would put emacs on a kitty
terminal on the same league as the full graphical version for my needs,
with the added benefit of dramatically reduced RAM footprint, faster
display and, last but not least, a truly great alternative to pgtk in
wayland.  So, if the implementation is feasible, i'd be willing to help
if needed.

Thanks,
jao
-- 
千里之行始於足下
The journey of a thousand miles begins with a single step.
  — 老子 (Lao Tsu) in Chapter 64 of 道德经 (Tao Te Ching)