On 8 July 2010 23:20, Joseph Wakeling <[email protected]> wrote:
> Can you explain more precisely ... ? This seems like something I should
> understand very well in order to provide an effective solution.
Context properties (using \set & \unset) are tied to engravers: they
provide information relevant to the generation of graphical objects.
Since transposition occurs at the music interpretation stage, it has
no direct connection with engravers: the pitch of a note is fixed
before a notehead is created. Consider the following minimal snippet:
{ c' }
This generates (simplified) a NoteEvent, with its pitch and duration
as event properties,
(make-music
'NoteEvent
'duration
ly:make-duration 2 0 1 1)
'pitch
(ly:make-pitch 0 0 0)
which the Note_heads_engraver hears. It passes this information on to
the NoteHead grob it creates from the event, so the head's correct
position and duration-log can be determined once it's ready for
printing.
If we transpose the snippet,
\transpose c d { c' }
the pitch is changed before it reaches the engraver (in fact, it
happens just after the parsing stage with the creation of a
TransposedMusic music object):
(make-music
'NoteEvent
'duration
(ly:make-duration 2 0 1 1)
'pitch
(ly:make-pitch 0 1 0)
You can see an example of a music property relevant to transposition:
untransposable.
\transpose c d { c'2 \withMusicProperty #'untransposable ##t c' }
-> the second c' remains untransposed.
Take a look at lily/music.cc to see where the transposition takes place.
Cheers,
Neil
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