What I want to do:
Percussion music has rolls, and while there are many references to
typesetting them, I haven't found good references to how to get them to
playback in a \midi {} block. My fantasy ideal is to have a "\roll" event
so I could do something like this:
sn4 sn4\roll sn4 sn4
and have the "sn4\roll" term effectively translated to "\repeat tremolo 16
sn64". This needs to be a function, as both the drumtype and note value
could be different (i.e. I could have a bd8\roll or other duration rolls on
other instruments).
I first tried this define-event-function:
Roll = #(define-event-function (myMusic) (ly:music?)
(make-music
'TremoloRepeatedMusic
'elements
'()
'repeat-count
16
'element
(make-music
'NoteEvent
'drum-type
'll
'duration
(ly:make-duration 6)
)
)
)
(I hardcoded the repeat-count and drum-type for testing before trying to
dynamically calulate those)
this generates the error:
error: post event function cannot return \repeat tremolo 16 sn64
So my assumption was that the "repeat tremolo" simply can't be in a post
event (please correct me if i'm wrong on this)
Changing to a music function:
Roll = #(define-music-function (myMusic) (ly:music?)
(make-music
'TremoloRepeatedMusic
'elements
'()
'repeat-count
16
'element
(make-music
'NoteEvent
'drum-type
'sn
'duration
(ly:make-duration 6)
)
)
)
This works with syntax of "sn4 \roll sn4 sn4 \roll sn4" (i.e. specifying
/roll before the note to indicate the next note is a roll) but is still
hardcoded values.
To get the make-music function to calculate the repeat-count, it should be
(64/duration) since an quarter note equals sixteen 64th notes, an eighth
note is eight sixteenth, etc. So I replaced the "16" value with "#(/ 64
ly:music-property myMusic 'duration)" so the function would do the math;
this generates the error of:
/usr/local/lilypond/usr/share/lilypond/current/scm/music-functions.scm:1407:9:
In procedure ly:repeated-music::unfolded-music-length in expression
(ly:music-length music):
/usr/local/lilypond/usr/share/lilypond/current/scm/music-functions.scm:1407:9:
Wrong type (expecting exact integer): #(/ 64 ly:music-property myMusic
(quote duration))
I'll admit I'm barely competent in Scheme, but this seems to say that the
math function is not returning an integer, but I'm not sure how to force
that.
Secondly, when I replace "'sn" with "ly:music-property myMusic 'drum-type"
I get this error:
fatal error: bad make-music argument: #<Duration 64 >
This i can't even begin to parse to understand what it doesn't like.
I'm lost, and would love some assistance on this. Even if that help is in
the form "you're on the completely wrong track, you should do xx.yy.zz
instead" that would be great.
Just for completeness, I'm attaching my full sample file in case the error
is not in the function itself but because I booched something else in the
file.
Thanks!
~Matt
\version "2.19.83"
Roll = #(define-music-function (myMusic) (ly:music?)
(make-music
'TremoloRepeatedMusic
'elements
'()
'repeat-count
#(/ 64 ly:music-property myMusic 'duration)
'element
(make-music
'NoteEvent
'drum-type
ly:music-property myMusic 'drum-type
'duration
(ly:make-duration 6)
)
)
)
one = {
\new DrumStaff
\drummode {sn4 \Roll sn4 sn4 sn4 }
}
\score {
\one
\layout { }
}
\score {
\unfoldRepeats \one
\midi { }
}
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