Re: Using path expressions to override stencils

[Paul Booker]

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) 
          (ly:stencil-scale
            customClefStencil
            mult mult))))
music =
\relative c' {
  \override Staff.Clef.stencil = \customClefStencil
  %\override Staff.Clef.stencil = \scaleCustomClefStencil
  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
  >>
%}