Hi everyone,
I was trying to use the \displaceHeads function from snippet 861 [1] [2]
on an eight-note chord, but found that it completely removes the beam
for some reason. I reduced it down to the following code:
\version "2.18.2"
{
\tweak before-line-breaking #(lambda (grob)
(ly:grob-property (ly:grob-object grob
'stem) 'stencil))
c'8[ c']
}
You can find a screenshot of the result at [3]. The function here
doesn’t mutate anything, but apparently just accessing the stem is
enough to render the associated beam invisible (at a guess, I’d say the
beam’s stencil is being unset somehow – it still influences the layout
otherwise). Is that a bug in LilyPond?
The \displaceHeads problem was previously reported at [4] (and I’ve
added the author to CC for this email), but as far as I can see the
thread didn’t go anywhere. (To answer the question in the reply [5] –
changing before-line-breaking to after-line-breaking fixes the beam, but
also removes the displacement effect, so as far as I can tell you might
as well just get rid of the \displaceHeads completely.) I hope the
reduced example above will help to get this bug (if it is one) fixed :)
An ugly workaround (back at the \displaceHeads level) is to remove all
the stem-related code and instead hard-code a value for the stem width –
the default seems to be 0.065. For convenience, you can find the result
at [6]. (If your stem width is different, take the original function,
replace the ly:grob-translate-axis! call with (display x-corr) in order
to print the correct value, and then substitute that.)
Cheers,
Lucas
[1]: http://lsr.di.unimi.it/LSR/Item?id=861
[2]: http://lsr.di.unimi.it/LSR/Snippet?id=861
[3]: https://i.imgur.com/hslsBDG.png
[4]: https://lists.gnu.org/archive/html/lilypond-user/2017-01/msg00214.html
[5]: https://lists.gnu.org/archive/html/lilypond-user/2017-01/msg00220.html
[6]:
https://gist.github.com/lucaswerkmeister/5ae87eaa3695b8a39f5d1e05bc9b077c
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