Hi all,
Ideally, for this sort of thing there should be a special grob. This grob
could also encompass the very common piano notation that shows that a note
ought to be taken by the other hand (the bracket with one wing).
The attached file creates a basic grob, which I've called PianoBracket.
Note that you can override its various properties like any other grob.
(I've shown some of what you can do in the file.) The vertical extent of
the brackets might be changed through PianoBracket.positions. (Which
function is lifted from the arpeggio code...differentiation can come later.)
The method for creating this is based on the regression test
input/regression/scheme-text-spanner.ly.
Note that what I've done here is not orthodox--it's "messing with
internals" as LilyPond currently has no user interface for building new
grobs. (You will get errors talking about redefinition of properties if
you compile multiple files at once using this engraver.)
Anyway, hope this proves useful!
--David
\version "2.19.15"
%% functions for grob creation are adapted from `scheme-text-spanner.ly'
#(define-event-class 'piano-bracket-event 'music-event)
#(define (add-grob-definition grob-name grob-entry)
(let* ((meta-entry (assoc-get 'meta grob-entry))
(class (assoc-get 'class meta-entry))
(ifaces-entry (assoc-get 'interfaces meta-entry)))
(set-object-property! grob-name 'translation-type? ly:grob-properties?)
(set-object-property! grob-name 'is-grob? #t)
(set! ifaces-entry (append (case class
((Item) '(item-interface))
((Spanner) '(spanner-interface))
((Paper_column) '((item-interface
paper-column-interface)))
((System) '((system-interface
spanner-interface)))
(else '(unknown-interface)))
ifaces-entry))
(set! ifaces-entry (uniq-list (sort ifaces-entry symbol<?)))
(set! ifaces-entry (cons 'grob-interface ifaces-entry))
(set! meta-entry (assoc-set! meta-entry 'name grob-name))
(set! meta-entry (assoc-set! meta-entry 'interfaces
ifaces-entry))
(set! grob-entry (assoc-set! grob-entry 'meta meta-entry))
(set! all-grob-descriptions
(cons (cons grob-name grob-entry)
all-grob-descriptions))))
#(define piano-bracket
(lambda (grob)
(let* ((th (ly:grob-property grob 'thickness 0.2))
(pro (ly:grob-property grob 'protrusion -0.5))
(pos (ly:grob-property grob 'positions))
(bracket (ly:bracket Y pos th pro))
(layout (ly:grob-layout grob))
(props (ly:grob-alist-chain grob
(ly:output-def-lookup layout 'text-font-defaults)))
(text (ly:grob-property grob 'text))
(text-stil
(ly:text-interface::interpret-markup layout props text))
(text-stil (ly:stencil-aligned-to text-stil Y 0))
(bracket-ext (interval-length (ly:stencil-extent bracket Y)))
(mid-bracket-pos (/ (+ (cdr pos) (car pos)) 2))
(text-stil
(ly:stencil-translate-axis text-stil mid-bracket-pos Y))
(padding (ly:grob-property grob 'padding))
(bracket
(ly:stencil-combine-at-edge bracket X 1 text-stil padding)))
bracket)))
#(add-grob-definition
'PianoBracket
`(
(direction . ,RIGHT)
(padding . 0.5)
(positions . ,ly:arpeggio::calc-positions)
(script-priority . 0)
(side-axis . ,X)
(staff-position . 0.0)
(stencil . ,piano-bracket)
(Y-extent . ,(grob::unpure-Y-extent-from-stencil ly:arpeggio::pure-height))
(Y-extent . ,grob::unpure-Y-extent-from-stencil)
(X-offset . ,ly:side-position-interface::x-aligned-side)
(Y-offset . ,ly:staff-symbol-referencer::callback)
(meta . ((class . Item)
(interfaces . (font-interface
side-position-interface
staff-symbol-referencer-interface
text-interface))))))
#(define piano-bracket-types
'(
(PianoBracketEvent
. ((description . "Used to signal vertical brackets to indicate hands in piano music.")
(types . (general-music piano-bracket-event event))
))
))
#(set!
piano-bracket-types
(map (lambda (x)
(set-object-property! (car x)
'music-description
(cdr (assq 'description (cdr x))))
(let ((lst (cdr x)))
(set! lst (assoc-set! lst 'name (car x)))
(set! lst (assq-remove! lst 'description))
(hashq-set! music-name-to-property-table (car x) lst)
(cons (car x) lst)))
piano-bracket-types))
#(set! music-descriptions
(append piano-bracket-types music-descriptions))
#(set! music-descriptions
(sort music-descriptions alist<?))
%%% based on `arpeggio-engraver.cc'
#(define piano-bracket-engraver
(lambda (grob)
(let ((event #f)
(bracket #f))
`((listeners
(piano-bracket-event .
,(lambda (engraver ev)
(if (not event)
(set! event ev)))))
(acknowledgers
(stem-interface .
,(lambda (engraver grob source-engraver)
(if (ly:grob? bracket)
(begin
(if (not (ly:grob-parent bracket Y))
(set! (ly:grob-parent bracket Y) grob))
(ly:pointer-group-interface::add-grob bracket 'stems grob)))))
(rhythmic-head-interface .
,(lambda (engraver grob source-engraver)
(if (ly:grob? bracket)
(ly:pointer-group-interface::add-grob bracket 'side-support-elements grob)))))
(process-music .
,(lambda (trans)
(if event
(set! bracket
(ly:engraver-make-grob trans 'PianoBracket event)))))
(stop-translation-timestep .
,(lambda (trans)
(set! event #f)
(set! bracket #f)))))))
pianoBracket = #(make-music 'PianoBracketEvent)
%%%%%%%%%%%%%%%%%%%%%% EXAMPLE %%%%%%%%%%%%%%%%%%%%%%%%%%%%
\score {
\new PianoStaff <<
\set PianoStaff.connectArpeggios = ##t
\new Staff {
s1
}
\new Staff <<
\clef bass
\new Voice {
\voiceOne
\override PianoBracket.text = #"RH"
\pianoBracket <e g b! dis'>2\arpeggio
\override PianoBracket.font-size = #-2
\pianoBracket <e g b! dis'>2\arpeggio
}
\new Voice {
\voiceTwo
\override PianoBracket.text = #"LH"
\pianoBracket <e, f, bes,>2\arpeggio
\override PianoBracket.protrusion = #-2
\override PianoBracket.font-size = #-2
\override PianoBracket.font-shape = #'italic
\pianoBracket <e, f, bes,>2\arpeggio
}
>>
>>
\layout {
\context {
\Global
\grobdescriptions #all-grob-descriptions
}
\context {
\Voice
\consists #piano-bracket-engraver
}
}
}
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