scheme function to extract a specific grob property from a music event?

[josé henrique padovani]

Hi,

I have tried to find in the manual and in the sources a scheme function 
that let me extract a specific grob from a music object...
I want to be able to know which is the 'staff-position (or should it be 
Y-offset?) grob-property of the notehead I am creating and use it to set 
the Y-offset of my markup.


As my last attempt storing and resetting scheme variables didn't worked, 
I'm following Mike Solomon suggestion and I have created a scheme 
function which writes everything I need...

Here is what I have until now....
The function has four entries: event-chord(music?) txt(markup?) 
numx(number?) numy(number?)
What I want to do is to eliminate the last argument by setting it to be 
equal to the same 'Y-offset (or 'staff-position, it is not clear to me 
yet) of the notehead....


%%%% CODE BEGIN
myfunction = #(define-music-function (parser location event-chord txt 
numx numy)
           (ly:music? markup? number? number?)
           (let ((result-event-chord (ly:music-deep-copy event-chord))
             (tscript-outside-staff-priority (make-music ;;\override 
TextScript #'outside-staff-priority = ##f
                              'ContextSpeccedMusic
                              'context-type
                              'Bottom
                              'element (make-music
                                'OverrideProperty
                                'pop-first
                                #t
                                'grob-property-path
                                (list (quote outside-staff-priority))
                                'grob-value
                                #f
                                'symbol
                                'TextScript)))
             (tscript-xoffset (make-music ;;;;;; \override TextScript 
#'X-offset = numx
                       'ContextSpeccedMusic
                       'context-type
                       'Bottom
                       'element
                       (make-music
                    'OverrideProperty
                    'pop-first
                    #t
                    'grob-property-path
                    (list (quote X-offset))
                    'grob-value
                    numx
                    'symbol
                    'TextScript)))
             (tscript-yoffset (make-music   ;;;;;  \override TextScript 
#'Y-offset = numy
                       'ContextSpeccedMusic
                       'context-type
                       'Bottom
                       'element
                       (make-music 'OverrideProperty
                    'pop-first
                    #t
                    'grob-property-path
                    (list (quote Y-offset))
                    'grob-value
                    numy
                    'symbol
                    'TextScript))))
        (set! (ly:music-property result-event-chord 'elements)
         (cons (make-music 'TextScriptEvent 'text (markup txt)) ;;;my 
markup
          (ly:music-property result-event-chord 'elements)))
        (make-music 'SequentialMusic 'elements (list 
tscript-outside-staff-priority tscript-xoffset tscript-yoffset 
result-event-chord))))

\score{
\relative c'{
%{
%\displayMusic
{
 \override TextScript #'outside-staff-priority = ##f
 \override TextScript #'X-offset = #2
 \override TextScript #'Y-offset = #0
 g'1-\markup{"<-"}
}
%}

\myfunction g'1 \markup{\sans "<-"} #2 #0
}
}

%%% CODE END


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