2008/12/14 Carl D. Sorensen <c_soren...@byu.edu>
>
>
>
> On 12/14/08 4:34 PM, "Trevor Bača" <trevorb...@gmail.com> wrote:
>
>
> >
> > I have a pretty big stockpile of tests and sometime in the next couple of
> days
> > I'll find a way to organize them and send them over. But I'd like to
> start
> > with the pair of examples that just seems absolutely pathological to me.
> Here
> > it is:
> >
> >
> > %%% VOICE-RESOLUTION EXAMPLE 1 %%%
> >
> > \version "2.11.57"
> >
> > {
> > \override Voice.NoteHead #'color = #red
> > c'8
> > d'8
> > e'8
> > f'8
> > \new Voice = "foo" {
> > g'8
> > a'8
> > b'8
> > c''8
> > }
> > d''8
> > e''8
> > f''8
> > g''8
> > }
> >
> > %%% END EXAMPLE 1 %%%
> >
> > So far, so good. In example 1, LilyPond creates two voices with one
> nested
> > inside the other. We see this because the outer eight notes are red while
> the
> > inner four notes are black.
> >
> > But now look at this:
> >
> > %%% VOICE-RESOLUTION EXAMPLE 2 %%%
> >
> > \version "2.11.57"
> >
> > {
> > \new Voice = "foo" {
> > \override Voice.NoteHead #'color = #red
> > g'8
> > a'8
> > b'8
> > c''8
> > }
> > d''8
> > e''8
> > f''8
> > g''8
> > }
> >
> >
> > %%% END EX 2 %%%
> >
> > (Stop and think what you'd expect here before looking at the output.)
> >
> > Here LilyPond renders a single voice! We see this because all eight notes
> are
> > red.
> >
> > Sprinkling the new \whichContext function before the first, fourth (and
> > eighth) notes in each example (where possible) makes it clear that the
> "foo"
> > context governs only the middle four notes in the first example while
> > governing *all* eight notes in the second example.
> >
> > What on earth is going on here?
> >
> > What's so odd is that if you look at example 2 and think "OK, this is all
> just
> > a single voice because the explicitly instantiated voice 'leaks' over
> into the
> > following four notes" ... then you're in for a big surprise when you add
> just
> > a single note to the beginning of the example:
> >
> > %%% EX 2 + 1 NOTE %%%
> >
> > {
> > c'8
> > \new Voice = "foo" {
> > \override Voice.NoteHead #'color = #red
> > g'8
> > a'8
> > b'8
> > c''8
> > }
> > d''8
> > e''8
> > f''8
> > g''8
> > }
> >
> > %%% END EX 2 MOD %%%
> >
> > That single note at the beginning now breaks the example into two voices
> just
> > like example 1!
> >
> > Can anyone explain what's going on here?
>
> In examples 1 and 2+1 note, the first music occurs without a voice being
> defined. Therefore, LilyPond creates (instantiates) a voice. Voice foo is
> then created, and limited to the notes contained in the brackets.
>
> In example 2, Voice foo is created before any voice is instantiated. Then,
> the music that comes after the voice foo definition is just applied to the
> existing voice foo, since there is no explicit instantiation.
OK, this explanation is extremely helpful. But there's still something
deeply wrong. Han-Wen from a bit earlier:
"Note that contexts do not 'nest' as you claim in a message below.
Voice contexts cannot contain any other context."
But check this out:
%%% VOICE-RESOLUTION EX 3 %%%
\version "2.11.65"
\include "english.ly"
\new Voice = "foo" {
\override Voice.NoteHead #'color = #red
\whichContext
c'8
cs'8
\new Voice = "bar" {
\override Voice.NoteHead #'color = #blue
\whichContext
d'8
ef'8
\new Voice = "blah" {
\override Voice.NoteHead #'color = #green
\whichContext
e'8
f'8
fs'8
g'8
}
\whichContext
af'8
a'8
}
\whichContext
bf'8
b'8
}
%%% END %%%
It appears as though the voice contexts are indeed nesting ... perfectly, in
fact!
And, in fact, John's new \whichContext function emits the following during
interpretation:
GNU LilyPond 2.11.65
Processing `0303.ly'
Parsing...
Interpreting music...
Current voice is foo
Current voice is bar
Current voice is blah
Current voice is bar
Current voice is foo
Preprocessing graphical objects...
Finding the ideal number of pages...
Fitting music on 1 page...
Drawing systems...
Layout output to `0303.ps'...
Converting to `./0303.pdf'...
This is nesting, isn't it? (How else to explain the stickiness of the grob
overrides?) Or have I completely lost my mind?
(Han-Wen's suggestion about looking over the iterator code makes sense and
I'll take a look right after I get in a quick jog ... because I think I
might go mildly insane otherwise ...)
>
>
> This kind of inconsistency shows up lots of times when you use automatic
> instantiation of contexts. In order to avoid these things, I've take to
> explicitly instantiating all contexts. (And if I used multiple books in a
> score, I'd explicitly instantiate all of them as well).
>
> Implicit instantiation is beginner-friendly but expert-unfriendly, IMO. It
> makes less for the user to type in building a simple song, but it hides the
> structure of LilyPond, and makes it unnecessarily difficult to set complex
> music.
>
> A while ago there was a post suggesting that we do away with all implicit
> instantiation and require users to explicitly instantiate contexts. That
> went nowhere. But I think there ought to be a statement somewhere that
> says
> "for complex scores, it is best to explicitly instantiate all voices". In
> my experience, that avoids lots of confusion.
>
--
Trevor Bača
trevorb...@gmail.com
<<attachment: example-3.png>>
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