Re: Stem duration

[David Kastrup]

Knut Petersen <address@hidden> writes:

> Am 05.07.2017 um 10:26 schrieb David Kastrup:
>> Knut Petersen <address@hidden> writes:
>>
>>> Shouldn't a stem not have a duration equal to the duration of the
>>> notehead it is attached to?
>> A stem could be attached to several different noteheads ("string
>> chords", usually arpeggiated in some manner).  LilyPond does not do this
>> well currently but that does not mean that it shouldn't: it is a common
>> type of notation.
> Interesting. Noteheads of different duration attached to a single stem?
> I don't remember to have seen something like that, and google does not
> really help. Which instrument uses such a notation, could you give an
> example?

I've seen it in the solo partitas and sonatas for violin from Bach and
would assume that they are also to be found in the cello suites.

>> So assigning a duration to a stem seems like something that would not
>> universally work anyway.
>
> Actually it's documented that stems have a duration,

Yes?

> and it would be quite useful for me:

> I try to extend my video generation script to change the color of the
> notes that are sounding at a certain moment. If there is a note still
> active in one voice while a new note is played in another voice _both_
> should be colored ... that's only easy/reliable if noteheads, rests,
> stems, flags and lyric syllables all have a correct duration.
>
> AFAICS only the duration of noteheads and rests is really usable in
> lilypond.

Well, you are right that Stem appears to have a duration callback.  But
your code does not even look at it.  It checks whether the Stem has a
cause that is an event (but stems are rather caused by noteheads) and if
it has (which it hasn't), you take the duration from there.

I haven't taken a look at just what the stem duration callback delivers
but I assume that with single or identical noteheads, the result should
be useful.

-- 
David Kastrup