Re: Can you determine why a grob is being typeset in scheme?

[Thomas Morley]

2015-04-20 23:45 GMT+02:00 David Nalesnik <address@hidden>:
> Hi Steven,
>
> On Mon, Apr 20, 2015 at 3:40 PM, Steven Weber <address@hidden> wrote:
>>
>> Since I always highlight clef changes in my music and I have access to a
>> color printer, I thought it’d be more efficient to let Lilypond do the
>> highlighting for me.  I wrote a handy function that places a filled-box
>> behind the clef grob, and it works great, as long as I add it manually for
>> every clef change.   What I really want is to add this to the Staff context
>> so I never have to think about it again.  So I created an override function
>> for the Staff.Clef.stencil which does the same thing as my manual function
>> and again, it does highlight the clefs.  Unfortunately, it highlights every
>> single clef (i.e., all the clefs at the beginning of the staves, not just
>> the clef changes), which is overkill and defeats the purpose of highlighting
>> things I need to pay attention to.
>>
>>
>>
>> Is there a way in scheme to say “is this grob being typeset because of an
>> explicit command (\clef bass), or implicitly (because of a line break)”?
>>
>>
>
>
> I can think of two ways to go about this.  Hopefully the first gives you
> what you want, because the second will take some doing.
>
> Breakable items like clefs have directions attached depending on where they
> are: -1 means end of line, 0 unbroken, and 1 beginning of line.  You can use
> the function ly:item-break-dir like so:
>
> \version "2.19"
>
> #(define highlight
>    (lambda (grob)
>      (let ((ibd (ly:item-break-dir grob)))
>        (if (= ibd 1) black green))))
>
> {
>   \override Staff.Clef.color = #highlight
>
>   c' d' e' f'
>   \clef bass
>   c d e f
>   \break
>   c d e f
>   \clef treble
>   c' d' e' f'
>   \break
>   c' d' e' f'
>   \clef bass
>   \break
>   c d e f
> }
>
>
> %%%
>
> One drawback here would be if you want to highlight both the cautionary clef
> and the beginning-of-line clef at the end of the example...  To do that and
> not catch other beginning-of-line clefs, we would have to use the other
> method, which is to insert the override into the music expression.
>
> I'm going to drop out at this point :)   But, as a head start, compare the
> results of running the following with the override left in or commented out:
>
> \displayMusic {
>   c'
>   %\override Staff.Clef.color = #highlight
>   \clef bass
>   c
> }
>
> The extending manual discusses this sort of manipulation with respect to
> music functions.  There are other useful commands like map-some-music which
> crop up periodically on the lists.
>
> Hope this is useful--
>
> David



Or maybe:

\version "2.19.18"

clef-color-engraver =
#(lambda (context)
 (let ((clef-props '()))

  `((acknowledgers
       (clef-interface
        . ,(lambda (engraver grob source-engraver)
             (let* ((clefGlyph (ly:context-property context 'clefGlyph))
                    (clefPosition (ly:context-property context 'clefPosition))
                    (clefTransposition
                      (ly:context-property context 'clefTransposition 0))
                    (new-clef-props
                      (list clefGlyph clefPosition clefTransposition)))
             ;(display (equal? clef-props new-clef-props))
             (if (and (not (equal? clef-props new-clef-props))
                      ;; to have the first clef colored as well
                      ;; comment next line
                      (not (null? clef-props))
                      )
                 (set! (ly:grob-property grob 'color) red))

             (set! clef-props new-clef-props))))))))

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

\layout {
  \context {
    \Staff
    \consists #clef-color-engraver
  }
}
<<
{
    \clef bass
    R1
    \break
    R1

    \clef alto
    R1
    \break
    \clef "G"
    R1
    \clef "G_8"
    R1
    \break
    R1
    \break
    R1
}

{
    R1
    \break
    R1
    R1
    \break
    \clef "mensural-c3"
    R1
    \clef "alto"
    R1
    \break
    R1
    \break
    R1
}
>>


Cheers,
  Harm