\hideNotes and MIDI Note_performer

[Adam Spiers]

Hi all,

I've noticed that MIDI generation doesn't honour transparent notes,
e.g. in

  f8( \hideNotes \grace {  c16 \glissando } \unHideNotes f8)

a NoteOn event is generated for the c16.  Hopefully I should be able
to address this if someone gives me a few pointers.  My first guess
was to tweak Note_performer::process_music() by adding something like:

        if (to_boolean(n->get_property ("transparent")))
                break;

but honestly it's a wild guess and was hoping someone could spend 2
minutes to save me spending several hours trying to grok the
Contributor's Guide.  My other thought was that if articulation.ly can
affect MIDI output then perhaps I'm better off tackling this in
scheme, since some people might very well want their transparent notes
appearing in the MIDI e.g. if they wanted to build "listen to this and
fill in the gaps in the transcription" aural exercises.

My LilyPond internals knowledge is rusty and pretty weak, but I'm
usually pretty good at picking new stuff up - would really appreciate
if someone could give me a leg up over the first hurdle though!

Thanks a lot,
Adam