Creating arbitrary lines (or other postscript things)

[Andrew C. Smith]

Dear users,

I'm working on a piece of music where certain notes need to be connected by 
dotted lines. I've tried a few different things: using \glissando and 
overriding the stencil to get a different position, or just creating \markup 
with a stencil object. I've also tried writing it in postscript (which seems to 
be the ideal solution) but I can't figure out how to return certain values of 
the notehead object. I'd like to avoid drawing the lines in by hand later, 
because I want to generate scores algorithmically.

What would be ideal (as far as I can tell) is to have a global variable that's 
a list of pairs of ly:music, then at the end of the program run a function to 
cycle through this list and draw dotted lines between all the pairs. My problem 
is that I can't figure out how to get the x/y position of the NoteHead object 
from a string of text like "d4", because as far as I've seen (and this may be 
way wrong, so forgive me) the interfaces generally are built for modifying 
values, not returning values for use in other functions. Any ideas? Or, at 
least places I should have already looked?

Have to admit I don't know Lilypond super well, but I've googled this problem 
pretty hard and read the manual looking specifically for it. I know mostly 
C-related languages, so Scheme is kind of bending my brain a little. Any help 
from more experienced users would be excellent. 

Thanks,

Andrew