Re: chaotic stems when querying direction property

[Neil Puttock]

On 13 August 2011 17:14, Ricardo Wurmus <address@hidden> wrote:

> I'm having a problem with a scheme engraver. Whenever I fetch the
> direction property of a grob's stem object (or directly through a
> listener on stem-event), the following warning is shown:
>
>   warning: no viable initial configuration found: may not find good
>            beam slope
>
> The resulting score has a few notes with their stems pointing in the
> wrong direction, so that the beams have a terribly ugly slope. As soon
> as I remove the code to store the direction everything is fine again.
>
> I've attached a simple demo file where the chaotic stem directions can
> be observed. All the code does is to save all grobs it encounters during
> the acknowledge phase and then query the direction for each stored grob
> during the processing phase.
>
> I'd be happy if you could explain to me why this happens.

The stems of beamed notes have a dependency on beam direction, so if
you try to get the direction of a stem which is part of a beam that
hasn't been completed it can mess up the calculation (i.e., you end up
with a disagreement between beam/stem directions in some cases).

Cheers,
Neil