Re: Using path expressions to override stencils

[Thomas Morley]

2016-02-16 19:40 GMT+01:00 Paul Booker <address@hidden>:
> Paul Morris <paul <at> paulwmorris.com> writes:
>
>>
>> > On Feb 16, 2016, at 8:35 AM, Paul Booker <Paul <at> homebass.net> wrote:
>> >
>> > I've only narrowed the problem down to the function
>>
>> Hi Paul,  Can you send a full but tiny example that we can run/test with
> LilyPond?  See:
>>
>> http://lilypond.org/tiny-examples.html
>>
>> That will make it easier to see what’s going on.
>>
>> -Paul
>> _______________________________________________
>
> Thanks Paul
> Good point. I should also offer the full path of the error message:
>
>
> /home/gub/NewGub/gub/target/mingw/src/lilypond-git.sv.gnu.or
> g--lilypond.git-release-unstable/lily/grob-property.cc,
> Line 243
>
> Expression:scm_is_null (value) || scm_is_eq (value, marker)
>
> The tiny example here is taken from LSR 623, and you can uncomment the line
> in the "music" variable which switches between overrides to invoke the error.
> I've included (commented out) the original scaled staves which demonstrate
> the capacity of the function:
>
> \version "2.19.36"
> customClefStencil =
>   #(ly:make-stencil
>     `(path 0.1
>           `(moveto 0 0
>             curveto 0 1 0.7 2.5 1.5 1.5
>             lineto 1.5 -3
>             closepath)
>           'round
>           'round
>           #t)
>      (cons 0 1.5)
>      (cons -3 2))
> scaleCustomClefStencil =
> #(lambda (grob)
>     (let* ((sz (ly:grob-property grob 'font-size 0.0))
>            (mult (magstep sz)))
>         (set! (ly:grob-property grob 'stencil)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Here you set the stencil-property.

>           (ly:stencil-scale
>             customClefStencil
>             mult mult))))
> music =
> \relative c' {
>   \override Staff.Clef.stencil = \customClefStencil
>   %\override Staff.Clef.stencil = \scaleCustomClefStencil
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Here you try to do it again.
But \scaleCustomClefStencil returns #<unspecified>!!
This will be visible if you look at the output of:

  \override Staff.Clef.stencil =
    #(lambda (grob)
      (display (scaleCustomClefStencil grob))
      point-stencil)

>   c1 g1
> }
> \new Staff
> \music
>
> %{
>   <<
>     \new Staff \with {
>         fontSize = #-3
>         \override StaffSymbol.staff-space = #(magstep -3)
>         \override StaffSymbol.thickness = #(magstep -3)
>     }
>     \music
>   \new Staff
>   \music
>     \new Staff \with {
>         fontSize = #2
>         \override StaffSymbol.staff-space = #(magstep 2)
>         \override StaffSymbol.thickness = #(magstep 2)
>     }
>     \music
>   >>
> %}
> _______________________________________________
> lilypond-user mailing list
> address@hidden
> https://lists.gnu.org/mailman/listinfo/lilypond-user

Try instead:

scaleCustomClefStencil =
#(lambda (grob)
    (let* ((sz (ly:grob-property grob 'font-size 0.0))
           (mult (magstep sz)))
          (ly:stencil-scale
            customClefStencil
            mult mult)))
music =
\relative c' {
  \override Staff.Clef.stencil = \scaleCustomClefStencil
  c1 g1
}

The LSR-snippet is wrong in this regard.
But 2.18.2 was more lax tolerating such things than new devel-versions.
I'll correct the LSR-snippet.

 Cheers,
   Harm