Re: Moving objects using "wrong" extent --- a question, valid solution needed!

[Mark Polesky]

Dmytro O. Redchuk wrote:
> I've found that it's possible to move objects (scripts,
> dynamics..) with "wrong" Y-extent so that they start to overlay
> other objects --- specifying Y-extent like #'(1 . -1) or like
> that
>
> [ ... ]
>
> So, now "i have a lot of questions", specifically:
> 1. Is it "valid" way? May this behavior be changed?
> 2. Which way would be more "valid"?


As documented in the IR, The default height of a hairpin is 0.6666
staff-spaces, so if you want the hairpin to make only enough space
for itself with no extra padding, you could do:

  \override DynamicLineSpanner #'Y-extent #'(-0.3333 . 0.3333)

If you want the surrounding items to be placed as if there were no
hairpin, use:

  \override DynamicLineSpanner #'Y-extent #'(0 . 0)

Personally, I don't see the benefit in making the lower extent
higher than the upper extent.  I think it makes things needlessly
confusing, and I don't think it was designed to be used that way.

Anyway, once you've overridden the DynamicLineSpanner, then you
can adjust the #'Y-offset, though I'd suggest overriding the
#'Y-offset for the Hairpin grob instead of the DynamicLineSpanner:

  \override DynamicLineSpanner #'Y-extent = #'(0 . 0)
  \override Hairpin #'Y-offset = #0.6666

So setting the Hairpin grob's #'Y-offset to its height value
(0.6666) centers the tip on the bottom staff-line.  Adding 1 to
the Y-offset moves it up another line.

If you want to be really fancy, you could write a music function
to do all the work for you:

setHairpinPosition =
#(define-music-function
     (parser location staff-position)
     (number?)
   #{
      \once \override DynamicLineSpanner #'Y-extent = #'(0 . 0)
      \once \override Hairpin #'Y-offset =
        #(lambda (hairpin-grob)
           (let ((hairpin-height
                  (ly:grob-property hairpin-grob 'height)))
             (+ 2 hairpin-height (/ $staff-position 2))))
   #})

Then you can just do:

  \setHairpinPosition #0

to put the hairpin tip on the middle line.  The music function
here interprets the numeric argument as a staff-position (ie.,
bottom line = -4, middle line = 0, top line = 4).

I also recommend using \once (as I've done in the above music
function).  Things get really confusing when an override is still
in effect from 4 pages ago.

Okay, so the only problem with all of this is that by overriding
the DynamicLineSpanner #'Y-extent, you not only affect the Hairpin
grobs, but unfortunately also the DynamicText grobs, and off the
top of my head, I don't see a trivial way around this.  This means
that if you do:

  \setHairpinPosition #0 c4\f\> c c c\!

...then the "f" dynamic will be open to collisions, such as with
the staff itself.  But maybe that won't be an issue with your
current project?  I don't know.

By the way, if you want the hairpin outside the staff, you'll
probably want to set the DynamicLineSpanner's #'Y-extent to
something other than #'(0 . 0).

Well, hopefully this points you in a better direction at least.
It's a bad idea to get in the habit of abusing syntax.

Hope this helps.
- Mark