Re: cross-staff, broken Glissando

[Jean Abou Samra]

(Adding Aaron in CC.)

Le 07/11/2021 à 12:39, Thomas Morley a écrit :
> Hi,
>
> commit 94860164493ab3a209986b0e3662ff7bd8958cb5
> Author: Mike Solomon <mike@apollinemike.com>
> Date:   Mon Mar 28 10:58:29 2011 -0400
>
>      Assures smooth transitions at glissando line breaks.
>
>      When a glissando breaks over lines, the left point of the beginning-of-line
>      glissando picks up on the y-axis where the right point of the end-of-line
>      glissando ends.
>
> is not true for cross-staff, broken Glissando.
> For a down-pointing Glissando, ending in a lower Staff this "pick-up"
> point is not matched.
> For an up-pointing Glissando starting in a lower Staff the first part
> is completely off. This is
> https://gitlab.com/lilypond/lilypond/-/issues/4806
> See attachment.


I get seemingly correct output in the issue's
example when adding

  \override Glissando.simple-Y = ##f

So I'd start by investigating why simple-Y was
added in the first place.


> While attempting to code stemmed Glissandi in scheme, there was a very
> helpful discussion starting here:
> https://lists.gnu.org/archive/html/lilypond-user/2021-10/msg00326.html
> lastly arriving at
> https://lists.gnu.org/archive/html/lilypond-user/2021-11/msg00003.html
> Basically I try to get start- and end-points of all kinds of
> Glissandi, printing crosses there.
> Many thanks to Aaron!
>
> That said,...
> If I always compensate the right ending-point with (pseudo-code)
> (ly:grob-relative-coordinate <Glissando-grob> <System-grob> Y)
> Then the crosses are at those positions Mike's patch promises.

Really System? Isn't this going to create a
cyclic dependency between the stencil and
vertical alignment for non-cross-staff glissandi
via VerticalAxisGroup skylines? Off the top I would
think it should be a matter of correcting
reference points (see above).


> I attach the new scheme-code and an image (with correct placed
> crosses, but untouched default-stencil)
>
> Ofcourse it's trivial to extend this scheme-code to create
> Glissando-stencil instead of those crosses.
> Better ofcourse is fixing the problem in our source.
>
> Alas, because my lack of C++-knowledge, I can't do it myself.

You should learn C++ someday :-)

Best,
Jean