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
\version "2.14.2"
#(define (grobParentByInterface grob intf axis)
(if (memq intf (ly:grob-interfaces grob))
grob
(grobParentByInterface (ly:grob-parent grob axis) intf axis)))
#(define (extent-combine extents)
(if (pair? (cdr extents))
(interval-union (car extents) (extent-combine (cdr extents)))
(car extents)))
#(define (crossStaffLength grob)
(let* ((papercolumn (grobParentByInterface grob 'paper-column-interface X))
(elementarray (ly:grob-object papercolumn 'elements))
(yref (ly:grob-common-refpoint-of-array grob elementarray Y))
(elements (ly:grob-object grob 'spanned-stems))
(extents (map (lambda (x) (ly:grob-extent x yref Y)) elements))
(foo (ly:message "extents: ~a" extents))
(maxextent (extent-combine extents))
(foo (ly:message "maxextent: ~a" maxextent))
(length (- (car maxextent) (cdr maxextent))))
length))
#(define (stemSpanStencil grob)
(let* ((length (crossStaffLength grob)))
(make-filled-box-stencil '(0.2 . 0.4) (cons 0 length))))
#(define (reparentStems ctx stems trans)
(if (and (pair? stems) (pair? (cdr stems)))
(let* ((stem (car stems))
(parent (ly:grob-parent stem Y))
(new-stem (ly:engraver-make-grob trans 'Stem '())))
(ly:message "stems: ~a" stems)
(ly:message "new-stem: ~a" new-stem)
(set! (ly:grob-property stem 'axes) (list X))
(ly:axis-group-interface::add-element stem new-stem)
(set! (ly:grob-object new-stem 'spanned-stems) stems)
(set! (ly:grob-object new-stem 'Y-offset) 5)
(set! (ly:grob-property new-stem 'stencil) stemSpanStencil)
(set! (ly:grob-property new-stem 'length) crossStaffLength))))
#(define (Cross_staff_stem_engraver ctx)
(let ((stems '()))
`((acknowledgers
(stem-interface
. ,(lambda (trans grob source)
(set! stems (cons grob stems)))))
(process-acknowledged
. ,(lambda (trans)
(reparentStems ctx stems trans) (set! stems '()))))))
\layout {
\context {
\PianoStaff
\consists #Cross_staff_stem_engraver
}
}
\new PianoStaff <<
\new Staff { \stemUp g' a' b' c'' }
\new Staff { \stemUp f' e' <f' d'> r }
>>
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