[GoLUG] Graphical output on xterm

[Kyle Terrien]

Hi all,

This is an old trick someone on Reddit told me years ago.  Did you
know that xterm can actually display vector graphics?

What you need:

+ GNU plotutils
+ xterm

Refer to “Simple examples using graph” [1].  Create a datafile with a
bunch of points like the following:

0.0  0.0
1.0  0.2
2.0  0.0
3.0  0.4
4.0  0.2
5.0  0.6

Then, in an xterm, run

graph -T tek < datafile

Xterm displays a secondary window with a line plot.

How does this work?

In $current_year, xterm can still emulate a Tektronix 4014 [2].  The
above graph command sends special escape codes that tell a Tektronix
terminal to switch to graphical mode and draw an image.  Xterm
understands these codes, opens a secondary window, and draws the
output.

Note that you must use xterm, because unfortunately more modern
VTE-based terminals like sakura, xfce4-terminal, and gnome-terminal do
not understand Tektronix codes.

Why is this so cool?

This is a 100% in-band method of drawing vector graphics over a pty.
It works over SSH, without X11 forwarding.  All you need is a
compatible terminal, i.e. xterm.

I suppose it is possible to display images using this method.  Such an
approach could be insanely useful for diagnostic commands because some
information is better formatted as a plot or image.  Maybe we could
have a graphical version of top that displays resource usage with
actual plots updated in real time.  Or maybe we can graph dependency
relationships of system services.

Someone wrote a tool for converting raster images to Tektronix codes
[3].  I suppose there must be a way to convert SVG, or maybe ditch the
SVG step entirely and output raw vector Tektronix codes.
(systemd-analyze plot should implement this.)

Another fun use would be to write games that use the Tektronix mode.
Because this is a vector format, I suppose it is possible to output
Asteroids.  Missile Command and Snake are other good contenders, or if
you are feeling truly edgy, try to reimplement “International
Thermonuclear War” from the movie /Wargames/.  It would look very
oldschool in this format.

--Kyle


[1]: https://www.gnu.org/software/plotutils/manual/en/html_node/Simple-Examples.html
[2]: https://en.wikipedia.org/wiki/Tektronix_4010
[3]: https://github.com/rricharz/make-tek-image

-- 
[*] Kyle Terrien
    Terrenus => from the Earth, to the Cloud
    https://terren.us/

Dilexisti justitiam, et odisti iniquitatem.  -- Psalmus 44:8