You guys are awesome! Took me a little bit to piece everything together, but here's what I wound up with. It's almost exactly what I want - I still need to figure out how to highlight clef changes in the first bar without highlighting the initial clef indicator, and how to deal with clef modifiers.
clef-highlight-engraver =
#(lambda (context)
(let ((clef-props '()))
`((acknowledgers
(clef-interface
. ,(lambda (engraver grob
source-engraver)
;; Only change items that are
non-default
(if (boolean? (ly:grob-property
grob 'non-default))
(begin
;; Grab all of
the data necessary
(let* ((clef
(ly:clef::print grob)) ;; The existing print object
(X-ext (ly:stencil-extent clef X)) ;; The X extent of the grob
(Y-ext (ly:stencil-extent clef Y))) ;; The Y extent of the grob
;; Pad
the X extent just a bit to make it look more like a highlighter
(set!
X-ext (cons (- (car X-ext) 0.25) (+ (cdr X-ext) 0.25)))
;; If
the clef is a bass clef, then we need to add just a smidge extra to the Y extent
;; This
is purely an aesthetic choice on my part, because I think the Y extent of the
;; bass
clef is a little off.
(if
(equal? (ly:context-property context 'clefGlyph) "clefs.F")
(set! Y-ext (cons (car Y-ext) (+ (cdr Y-ext) 0.15))))
;;
Don't do this for the initial clef
;;
NOTE: If you have a clef change in the first bar, it won't be highlighted.
;;
Is there a better way to determine the first (and only the first)
clef change?
(if
(not (equal? (ly:context-property context 'currentBarNumber) 1))
(begin
(set! (ly:grob-property grob 'layer) -10)
(set! (ly:grob-property grob 'stencil)
(ly:stencil-add
(ly:make-stencil (list 'color (x11-color 'yellow)
(ly:stencil-expr (ly:round-filled-box X-ext
Y-ext 0)) X-ext Y-ext)) clef)))))))))))))
Thanks again for your help!
--Steven
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