PostScript file with /vertex and /poly definitions useful for drawing graphs, with demo

ps_done.ps

%!

0 setlinewidth

/Times-Roman findfont 12 scalefont setfont

newpath 8 99 moveto 601 99 lineto 601 692 lineto 8 692 lineto closepath stroke

/vertex { 2 copy 5 4 roll dup 4 1 roll
  newpath 0 360 arc closepath
  gsave 1.0 setgray fill grestore
  stroke
  12 ge { 
    newpath moveto
    gsave dup false charpath flattenpath pathbbox grestore
    exch 4 1 roll exch sub -.5 mul 3 1 roll sub -.5 mul exch
    rmoveto show
  } { pop pop pop } ifelse
} def

/txt {
  newpath moveto
  gsave dup false charpath flattenpath pathbbox grestore
  exch 4 1 roll exch sub -.5 mul 3 1 roll sub -.5 mul exch
  rmoveto show
} def

/txtdistdeg {
  newpath moveto
  gsave dup false charpath flattenpath pathbbox grestore
  exch 4 1 roll exch sub -.5 mul 3 1 roll sub -.5 mul exch
  5 3 roll gsave
  rotate 0 exch rmoveto
  rmoveto show
  grestore
} def

/poly {
  newpath
  moveto
  {
    count 0 eq { exit } if
    lineto
  } loop
} def


%% http://computer-programming-forum.com/36-postscript/3d1b79b93a578811.htm
/arrow          %% angle /arrow -- draws arrowhead
{
gsave
  currentpoint translate 90 sub rotate .5 .5 scale
  newpath
  0.1 setlinewidth
  0 -15 moveto
  -6 -18 lineto
  -4 -15 -1 -9 0 0 curveto
  1 -9 4 -15 6 -18 curveto
  0 -15 lineto
  fill
grestore
} def

/arrowto        %% x1 y1 arrowto -- draws line with arrowhead
{
2 copy                  % x1 y1 x1 y1
currentpoint            % x1 y1 x1 y1 x0 y0
3 -1 roll exch          % x1 y1 x1 x0 y1 y0
sub                     % x1 y1 x1 x0 y1-y0
3 1 roll                % x1 y1 y1-y0 x1 x0
sub                     % x1 y1 y1-y0 x1-x0
atan                    % x1 y1 theta
3 1 roll                % theta x1 y1
2 copy lineto           % theta x1 y1
2 copy stroke moveto    % theta x1 y1
3 -1 roll arrow         % x1 y1
moveto
} def

/rarrowto {     %%  dx dy rarrowto --
exch currentpoint       % dy dx x0 y0
4 1 roll                % y0 dy dx x0
add 3 1 roll            % x0+dx y0 dy
add arrowto
} def


%% len dist cr cg cb angle x1 y1
/parrow {
  gsave
  newpath translate 0 0 moveto
  rotate
  setrgbcolor
  0 exch rmoveto
  0 rarrowto 
  grestore
} def

.75 setgray 300 400 200 400 200 300 275 325 poly fill

0 setgray 300 400 200 400 200 300 275 325 poly closepath stroke 

(89) 18 300 400 vertex
(123) 12 200 400 vertex
(3) 6 200 300 vertex
(55) 9 275 325 vertex

(txt) 350 250 txt

() 0.3 390 270 vertex
12 60 (60 deg) 390 270 txtdistdeg
12 240 (240 deg) 390 270 txtdistdeg

() 0.3 380 350 vertex
30 6 0 1 0 60 380 350 parrow
30 6 0 0 1 240 380 350 parrow

showpage

Added color arrow vectors (parallel to undirected graph edge), based on 2000 public domain arrow code (bottom):
http://computer-programming-forum.com/36-postscript/3d1b79b93a578811.htm

%% len dist cr cg cb angle x1 y1
/parrow {
...
}
...
() 0.3 380 350 vertex
30 6 0 1 0 60 380 350 parrow
30 6 0 0 1 240 380 350 parrow

Not part of ps_done.ps anymore, but nice automatic "arrow at vertex" can be generated from code by NodeJS "vertex_indicator()" function
https://github.com/Hermann-SW/planar_graph_playground/blob/main/ps.js#L250-L289
to visualize "traversing a face":

https://forums.raspberrypi.com/viewtopic.php?t=333342&start=25#p2010496