Re: grace note bug?

[David Nalesnik]

Hi Jaime,

On Sat, Jan 3, 2015 at 6:02 PM, Jaime E Oliver <address@hidden> wrote:

Hi everyone,

I am not sure if this is a bug, or just improper use, but, when using a single grace note _expression_ with two notes such as:
\slashedGrace {a'32 a32}
I get the expected result.

But when I use two subsequent ones such as:
\slashedGrace {a'32} \slashedGrace {a32}
I get the wrong score representation.

There is no support (as far as I know) for slashed grace note groups.

There is a workaround, however.  Try this:

\version "2.19.15"

%%%%% A better slash snippet %%%

% The argument `ang' is the amount of slant, expressed in degrees.

%

% Stem-fraction is the distance between the point the slash crosses the stem

% and the notehead-end of the stem.  It is expressed as a number between 0 and 1.

%

% The argument `protrusion' is the extra distance the slash

% extends beyond its intersection with stem and beam

slash =

#(define-music-function (parser location ang stem-fraction protrusion)

   (number? number? number?)

   (remove-grace-property 'Voice 'Stem 'direction) ; necessary?

   #{

     \once \override Stem #'stencil =

     #(lambda (grob)

        (let* ((X-parent (ly:grob-parent grob X))

               (is-rest? (ly:grob? (ly:grob-object X-parent 'rest))))

          (if is-rest?

              empty-stencil

              (let* ((ang (degrees->radians ang))

                     ; We need the beam and its slope so that slash will

                     ; extend uniformly past the stem and the beam

                     (beam (ly:grob-object grob 'beam))

                     (beam-X-pos (ly:grob-property beam 'X-positions))

                     (beam-Y-pos (ly:grob-property beam 'positions))

                     (beam-slope (/ (- (cdr beam-Y-pos) (car beam-Y-pos))

                                   (- (cdr beam-X-pos) (car beam-X-pos))))

                     (beam-angle (atan beam-slope))

                     (stem-Y-ext (ly:grob-extent grob grob Y))

                     ; Stem.length is expressed in half staff-spaces

                     (stem-length (/ (ly:grob-property grob 'length) 2.0))

                     (dir (ly:grob-property grob 'direction))

                     ; if stem points up. car represents segment of stem

                     ; closest to notehead; if down, cdr does

                     (stem-ref (if (= dir 1) (car stem-Y-ext) (cdr stem-Y-ext)))

                     (stem-segment (* stem-length stem-fraction))

                     ; Where does slash cross the stem?

                     (slash-stem-Y (+ stem-ref (* dir stem-segment)))

                     ; These are values for the portion of the slash that

                     ; intersects the beamed group.

                     (dx (/ (- stem-length stem-segment)

                           (- (tan ang) (* dir beam-slope))))

                     (dy (* (tan ang) dx))

                     ; Now, we add in the wings

                     (protrusion-dx (* (cos ang) protrusion))

                     (protrusion-dy (* (sin ang) protrusion))

                     (x1 (- protrusion-dx))

                     (y1 (- slash-stem-Y (* dir protrusion-dy)))

                     (x2 (+ dx protrusion-dx))

                     (y2 (+ slash-stem-Y

                           (* dir (+ dy protrusion-dy))))

                     (th (ly:staff-symbol-line-thickness grob))

                     (stil (ly:stem::print grob)))

                (ly:stencil-add

                 stil

                 (make-line-stencil th x1 y1 x2 y2))))))

   #})

\new Staff {

  \relative c'' {

    a4

    \grace {

      \slash 50 0.6 1.0 a'32 a

    }

    d,4 d2

  }

}

Code comes from the following discussion: http://www.mail-archive.com/lilypond-user%40gnu.org/msg86544.html

Hope this helps,

David