Re: Cross-staff stem engraver (was: New frog in an empty pond?)

[Pavel Roskin]

Hello, Joe!

> In case it wasn't clear from what I said before, engravers in lilypond
> don't do the actual layout. Instead, they build the grobs and set up
> the connections between them. Most of the layout is done in callback
> functions.

Yes, I realize it now.  Your suggestion to create a new stem worked
fine.  I can get the relative coordinates of themes on different staves.

The attached file shows where I am now.  There are many minor issues,
and I hope I can solve most of them, but I'll certainly appreciate help.

I'm getting a message "Weird stem", and I don't see how to avoid it.
Perhaps I should create a totally new grob with a unique name, such as
StemSpan.  Is that possible?  What would be needed?

How do I make the new stem start at the same point as the original
one.  I tried this:

(set! (ly:grob-property stem 'axes) (list X))

I don't understand how it works.  Not setting axes leads to:

programming error: axes should be nonempty

Maybe I should use some other parent for the new stem?

The new stems are offset horizontally on purpose to see where they
are.  But the vertical position is wrong and I don't see how to fix it.

I'll appreciate if you have a look at the code.

-- 
Regards,
Pavel Roskin

stemspan.ly
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