Re: Catch direction operators

[Thomas Morley]

2013/9/29 David Kastrup <address@hidden>:
> Urs Liska <address@hidden> writes:
>
>>>You can write:
>>>
>>>#(define-music-function (parser location item)
>>>   (symbol-list-or-music?)
>>>   (define (grob-colorize-dir grob)
>>>     (let ((ev (event-cause grob)))
>>>       (case (ly:event-property ev 'direction)
>>>             ((1) red)
>>>             ((-1) blue)
>>>             (else '())))))
>>>   #{ \tweak color #grob-colorize-dir #item #})
>>
>> Thanks, this works perfectly.
>>
>> I would like to add this to a Frescobaldi addition and later (once
>> 2.18 is out) to a LilyPond addition proposal. Do you have any
>> objections?
>
> You can add it wherever you want.  I don't see it making any sense as an
> addition to LilyPond proper as it is a rather special use case.  It may
> still be nice as a snippet as it is simple, flexible, and powerful.  The
> use cases also show \tweak as an internal workhorse for both tweaks and
> overrides.
>
> As a snippet, it makes sense _in_ 2.18 as it illustrates current
> programming techniques.
>
> --
> David Kastrup



Hi,

I thought it would be nice to apply such a function to not only one
grob, but rather a list of grobs or all possible grobs.
Though, I didn't manage to generalize David K's tweak-function.
Instead I come up with the code below.
Frankly, I now have the problem that I don't know how to revert it in
a music-expression or how to apply it once. :(

\version "2.17.26"

%#(define highlighting-colors `(,(rgb-color 0 1 1) ,(x11-color 'SlateBlue2)))

#(cond ((not (defined? 'highlighting-colors))
        (define highlighting-colors `(,red ,green))))

#(define grob-colorize-dir
 (lambda (grob)
  (let* ((ev (event-cause grob))
         (color (if (ly:prob? ev)
                    (case (ly:event-property ev 'direction)
                       ((1) (car highlighting-colors))
                       ((-1) (cadr highlighting-colors))
                       (else '()))
                    '())))
    (ly:grob-set-property! grob 'color color))))

#(define (apply-colored-if-changed l)
  (let* ((grobs-copy all-grob-descriptions)
         (grobs-to-consider
           (cond ((eq? l 'all-grobs)
                   grobs-copy)
                 ((symbol? l)
                   (list (assoc l grobs-copy)))
                 ((list? l)
                   (map
                     (lambda (grob)
                       (assoc grob grobs-copy))
                       l))
                 (else '()))))

  (lambda (context)
   (let loop ((x grobs-to-consider))
    (if (not (null? x))
     (let ((grob-name (caar x)))
      (ly:context-pushpop-property
         context
         grob-name
         ;; TODO: Go for 'color directly?
         'after-line-breaking
         grob-colorize-dir)
      (loop (cdr x))))))))

colorChanges =
#(define-music-function (parser location s-or-l)
   (symbol-list-or-symbol?)

#{
        \applyContext #(apply-colored-if-changed s-or-l)
#})

%%%%%%%%%%%%%%%
% EXAMPLE
%%%%%%%%%%%%%%%

\layout {
  \context {
    \Voice
    %% possible use-cases:
    %\colorChanges #'all-grobs
    \colorChanges #'(Slur StringNumber TextScript)
    %\colorChanges #'Slur
  }
}

{
    a4-( b)
    a4^( b)
    a''4_( b)

    c''-3\4-"xy"
    c''_3^\4^"xy"
    c''^3_\4_"xy"
}

Nevertheless, hth
  Harm