Change stem stencil

[Jon Arnold]

Hi-

I am trying to notate a harp string muffle like here: https://s3.amazonaws.com/cdn.harpcenter.com/images/extras/MufflesEx10R10.jpg

I found a script by Peter Bjuhr that successfully replaces the stem (modified for glyph I need): https://lists.gnu.org/archive/html/lilypond-user/2014-02/msg00665.html

#(define (muffle-stem grob)

    (if (ly:stencil? (ly:stem::print grob))

      (let* ((stencil (ly:stem::print grob))

             (X-ext (ly:stencil-extent stencil X))

             (Y-ext (ly:stencil-extent stencil Y))

             (width (interval-length X-ext))

             (len (interval-length Y-ext)))

        (ly:stencil-translate

          (grob-interpret-markup grob

            (markup #:smuflglyph "stemDamp"))

          (cons 0 (interval-start Y-ext))))

      #f))

My only problem is that the Smufl glyph doesn't flip vertically with the stem, so it doesn't look right on down-stems. Can anyone help enhance the script to account for stem direction?

Thanks so much-

Jon Arnold