Re: Directional NoteHead Stencil Support

[David Nalesnik]

Hi,

On Fri, Mar 20, 2015 at 7:14 AM, Paul Morris <address@hidden> wrote:

There's a snippet in the lsr for accessing grobs "laterally" from another grob's callback:

http://lsr.di.unimi.it/LSR/Item?id=621

...like accessing the stem grob from a note head grob.  There's also one on showing "grob ancestry" that's helpful for this kind of thing.

This is a helpful snippet.

If you look at the various interface pages, under "Internal Properties" in the Internals Reference, you'll find other grobs (single grobs or multiple grobs stored in a "grob-array") that your grob stores pointers to, meaning that you have easy access to the other object(s).  The grob NoteHead has "rhythmic-head-interface" (see bottom of page at http://lilypond.org/doc/v2.19/Documentation/internals/notehead).  Under the Internals page for that interface  

http://lilypond.org/doc/v2.19/Documentation/internals/rhythmic_002dhead_002dinterface

we find:

Internal properties:

dot (graphical (layout) object)

A reference to a Dots object.

stem (graphical (layout) object)

A pointer to a Stem object.

With ly:grob-object, we can get at either a Dot or a Stem.

So, with your function you could write:

#(define alt-notehead

   (lambda (grob)

     (let ((stem (ly:grob-object grob 'stem)))

       (if (ly:grob? stem) ;; perhaps unnecessary, but let's be safe

           (if (eq? (ly:grob-property stem 'direction) DOWN)

               (grob-interpret-markup grob stil)

               (grob-interpret-markup grob newstil))))))

Finding the path from one object to another is usually just a matter of trial-and-error, following this path, following that path, until you reach the pot of gold.

HTH,

David