lilypond-learning: Advanced tweaks with Scheme
4.7.5 Advanced tweaks with Scheme
---------------------------------
Although many things are possible with the ‘\override’ and ‘\tweak’
commands, an even more powerful way of modifying the action of LilyPond
is available through a programmable interface to the LilyPond internal
operation. Code written in the Scheme programming language can be
incorporated directly in the internal operation of LilyPond. Of course,
at least a basic knowledge of programming in Scheme is required to do
this, and an introduction is provided in the 
(lilypond-extending)Scheme tutorial.
As an illustration of one of the many possibilities, instead of
setting a property to a constant it can be set to a Scheme procedure
which is then called whenever that property is accessed by LilyPond.
The property can then be set dynamically to a value determined by the
procedure at the time it is called. In this example we color the note
head in accordance with its position on the staff.
#(define (color-notehead grob)
"Color the notehead according to its position on the staff."
(let ((mod-position (modulo (ly:grob-property grob 'staff-position)
7)))
(case mod-position
;; Return rainbow colors
((1) (x11-color 'red )) ; for C
((2) (x11-color 'orange )) ; for D
((3) (x11-color 'yellow )) ; for E
((4) (x11-color 'green )) ; for F
((5) (x11-color 'blue )) ; for G
((6) (x11-color 'purple )) ; for A
((0) (x11-color 'violet )) ; for B
)))
\relative c' {
% Arrange to obtain color from color-notehead procedure
\override NoteHead.color = #color-notehead
a2 b | c2 d | e2 f | g2 a |
}
[image src="" alt="[image of music]" text="image of music" ]
Further examples showing the use of these programmable interfaces can
be found in (lilypond-extending)Callback functions.
Info Catalog
lilypond-learning: Other sources of information
lilypond-learning: Further tweaking