\arrow markup command

[Simon Albrecht]

Hello,

I have just been annoyed by the fact that it takes four commands 
(\combine, \arrow-head, \override, and \draw-line) to draw an acceptable 
arrow-head (\override is to match the thickness of the line to the Feta 
glyph), so I proceeded to code an \arrow markup command simplifying the use.

Find the code with an example attached.

I will put it up for review as normal, but I want to ask one design 
question first:

It struck me as simplest to have this function supersede the \arrow-head 
function. I didn’t fully carry that out in the example, but I think the 
use cases for printing a single arrow-head are much fewer than for 
printing a complete arrow, and there are already so many markup 
functions around, that I think it would be better to have only one 
function. [1]

Though this actually raises a second question: Why does the Feta font 
have one glyph for each of the 4 directions in which an arrow head 
generated with \arrow-head can point? Why not simply rotate one glyph in 
the first place? (I’m sure the Metafont code does just that, though it 
would strike me more logical to do it on a ‘higher’ level.)

Best, Simon

[1] One could probably write a convert-ly rule as well (sorry, I can’t, 
not knowing Python), though such a rule would have to compute a rotation 
angle from the axis and dir properties:

axis 0/X  dir 1/RIGHT  ->  ang 0
axis 0/X  dir -1/LEFT  ->  ang 180
axis 1/Y  dir 1/UP     ->  ang 90
axis 1/Y  dir -1/DOWN  ->  ang -90

arrow.ly
Description: Text Data

arrow.preview.png
Description: PNG image