Re: skylines and custom-code

[Carl Sorensen]

On 4/8/21, 8:22 AM, "lilypond-user on behalf of Kevin Barry" 
<lilypond-user-bounces+carl.d.sorensen=gmail.com@gnu.org on behalf of 
barrykp@gmail.com> wrote:
    
    I haven't had time to try and understand your issue, but having worked
    on problems with Stems and Beams in the past I think it's an area of the
    code that could be improved, because there is an effective circular
    dependency:
    - Stems check Beams in order to determine their direction/position etc
    - Beams check where the first and last noteheads are - compared to the
      whole system - to try and figure out on which side they should be on
      or if the beam should be kneed, etc
    - Checking where noteheads are in relation to the whole system triggers
      lots of other grob calculations. If any of these calculations check
      the Beam or the Stem you get a circular dependency (I fixed at least
      one regression in this area where DynamicText was triggering the
      circular dependency).

I think you've done the community a great service by making this process 
explicitly explained.  Thanks for doing this!

    - If you try to dive into all the consequences of the code that
      calculates a Stem's direction it is almost impossible to understand.
      It's a long chain of pure/unpure calls - maybe 50 stack frames of just
      that stuff (IIRC); completely impenetrable (for me at any rate)
    - In my opinion, the fix is to find a way to figure out notehead
      positions without calculating everything else, then Beams, then Stems

The problem with this proposed fix is that it would eliminate optical spacing, 
which is one of the LilyPond claims to fame for producing beautiful sheet 
music.  A stem-up note followed by a stem-down note deliberately has different 
spacing than a stem-down note followed by a stem-up note.

    
    I doubt that is any help to you, but perhaps someone else will read this
    and know more.
    
    Kevin
    
Thanks,

Carl