Re: \oneVoice and \voiceXX commands having the wrong scope

[Yuval Harel]

On Sat, 29 Jan 2005 17:17:38 -0800, Graham Percival <address@hidden>  
wrote:
> On 28-Jan-05, at 8:28 AM, Yuval Harel wrote:
> > This example is a very useful. Until now I didn't understand why the  
> > two different syntaxes
> > << {} {} >> and << {} \\ {} >> were necessary.
> > I think it should appear in the documentation (with the addition of  
> > \voiceOne and \voiceTwo to avoid collisions and the "Too many clashing  
> > notecolumns." warning), along with
> > explanation that the << \\ >> approach produces separate voices, and  
> > some examples showing
> > how voice flow in and out of such constructs (perhaps using slurs).
> > I'm willing to write this (and send it to the development list? to  
> > Graham?)
>
> Great!  Please send it to lilypond-devel.
>
> I've updated the polyphony docs somewhat in 2.5.x; please have a look at  
> them
> and suggest changes / additions.
>
> Cheers,
> - Graham


Hi,

I'm working on updating the polyphony documentation. However, there are  
some things I want to write about, but don't understand well enough, so  
here are some questions:

1) What is the meaning of \shiftXXX commands (i.e. the meaning of the  
#'horizontal-shift property), and how does Lilypond resolve collisions  
between voices? The best guess I have at how this work is this cumbersome  
description:
When two notes appear in two different voices simultaneously:
	- If both voices have the same shift and stem direction, the two notes  
are vertically alligned, no collision resolution is not attempted, and a  
warning is produced.
	- If the voices have the same shift in different stem directions, the  
notes are vertically alligned, unless collision resolution shifts them  
horizontally.
	- If the voices have different shift, they will never be alligned. If  
possible, only the note with the greater horizontal-shift will be shifted,  
in the direction clockwise to the stem direction.
I tried experimenting a bit to verify that, but it appears to be wrong,  
e.g. in:
\new Staff \transpose c c' { <<
    {\stemUp a'}
    \new Voice {\stemUp c}
    \new Voice {\shiftOn \stemUp a}
> >
all voices are alligned horizontally. Removing the {c} makes the two {a}s  
not be alligned.
Also, why do shifts exist at all, instead of being a part of the  
collision-resolution mechanism? The only use I see for the seperation is  
to bypass the collision-resolution by defining both voices with the same  
shift and stem direction (the same \voiceXXX command}. But I suspect this  
is not the reason, since doing so produces a warning.

2) What is the exact meaning of "\\". For example, what is the meaning of  
constructs only partially divided by "\\", such as:
<< {..} {..} \\ {..} >>
and why?

3) The current documentation notes that voices in << {...} \\ {...} >>  
constructs are named "1","2" etc. What is the name of the main voice  
(outside of these constructs)?

Thanks,
        Yuval