Re: warnings during `make web'

[Juergen Reuter]

On Mon, 6 Nov 2006, Juergen Reuter wrote:

> On Mon, 6 Nov 2006, Han-Wen Nienhuys wrote:
>
> > Without knowing the details, I think it is easiest to define a 
> > LigatureNoteHead or XxxxxLigatureNoteHead, and a  XxxxLigature in 
> > define-grobs.scm.  (Xxxxx = Gregorian, Vaticana, Coherent, Mensural)
> >
> > By copying some definitions of the NoteHead grob, some C++ of Note_head can 
> > be shared.
> >
> > A special XXX_Ligature engraver will create those heads, and arrange them 
> > correctly within the appropriate XxxxLigature. If the XxxxxLigature is an 
> > Item, then it will be on a single PaperColumn.  By putting the 
> > XxxxNoteHeads on the XxxxxLigature Item, the notes will also be on the same 
> > PaperColumn. The XxxxLigature knows all of the ligature contents, and 
> > hence, it can determine the final desired shape.
>
> Ok, this may work provided that there is no code elsewhere in lily that 
> receives grobs, looks into them and does some things if and only if this grob 
> is a NoteHead.  Otherwise, this code would not apply to ligature heads, thus 
> failing special treatment of note heads that should also apply on ligature 
> heads.  I actually tried this approach a couple of years ago, and it did not 
> work for this reason.  Of course, lily has changed dramatically since then; 
> probably I should try again.

Actually, the above approach will not work without further modification:

Currently, note-heads-engraver.cc listens for note events and creates 
NoteHead grobs; the ligature engraver "takes over" these note heads and 
manipulates them.  To follow the above approach, I would have to make the 
note heads engraver stop producing note head grobs (and instead let the 
ligature engraver produce LigatureHead grobs).  But how can I achieve 
this?  Removing the note heads engraver completetly from its context is no 
option, since both usual note heads as well as ligatures have to appear in 
the same context.

So, how can I signal the note heads engraver that a ligature is in process 
and that it should stop producing note heads?

Greetings,
Juergen