%% This snippet defines functions that enable "1/2" pedal indications
%% to be used.  Using this is quite easy, just add \sustainHalfOn
%% in place of \sustainOn and \sustainHalfOff in place of \sustainOff
%%
%% This implementation fully supports 'mixed, 'text, and 'bracket pedal modes
%%
%% The new functions will honor the value of Staff.sustainPedalStyle when
%% doing the rendering.
%%
%% The implementation of these functions is a bit complicated.  In order to
%% force a new pedal indication when changing from half pedal to full pedal
%% or vice versa in mixed or bracket mode, internally this implementation
%% represents the half pedal events as UnaCorda pedal events.  Basically,
%% when \sustainHalfOn is called, we temporarily change the rendering
%% of the UnaCorda pedal indications so they look like a half pedal.
%% When \sustainHalfOff is called, they are changed back.  A side effect of
%% this is that having the UnaCorda pedal and 1/2 pedal active at the
%% same time is not possible with this implementation.

%% Definitions of half-pedal functions.  Moving these to a Lilypond include file is recommended.

#(define (half-pedal-stencil grob)
  (grob-interpret-markup 
    grob 
    (markup #:raise 0.1 "½" #:hspace -0.5 #:musicglyph "pedal.Ped")))

#(define (add-sustain-on note-event)
  (set! (ly:music-property note-event 'articulations)
   (cons
    (make-music 'UnaCordaEvent 'span-direction -1)
    (ly:music-property note-event 'articulations)))
  note-event)

#(define (override-una-corda-strings)
  (context-spec-music
   (make-sequential-music
    (list
     (make-property-set 'pedalUnaCordaStrings (list "Ped." "*Ped." "*"))
     (make-apply-context
      (lambda (context)
       (ly:context-set-property! 
         context 
         'pedalUnaCordaStyle 
         (ly:context-property context 'pedalSustainStyle))))))
   'Staff))

#(define (revert-una-corda-strings)
  (context-spec-music
   (make-sequential-music
    (list
     (make-property-unset 'pedalUnaCordaStrings)
     (make-property-unset 'pedalUnaCordaStyle)))
   'Staff))

#(define (add-sustain-off note-event)
  (set! (ly:music-property note-event 'articulations)
   (cons
    (make-music 'UnaCordaEvent 'span-direction 1)
    (ly:music-property note-event 'articulations)))
  note-event)

#(define (use-half-pedal-stencil)
  (context-spec-music
   (make-grob-property-set
    'UnaCordaPedal
    'stencil
    half-pedal-stencil)
   'Staff))

#(define (revert-pedal-stencil)
  (context-spec-music
   (make-grob-property-revert
    'UnaCordaPedal
    'stencil)
   'Staff))

sustainHalfOn =
#(define-music-function
  (note)
  (ly:music?)

  (make-sequential-music
   (list
    (override-una-corda-strings)
    (use-half-pedal-stencil)
    (add-sustain-on note))))

sustainHalfOff =
#(define-music-function
  (note)
  (ly:music?)
  (make-sequential-music
   (list
    (revert-pedal-stencil)
    (add-sustain-off note)
    (revert-una-corda-strings))))

%% Half Pedal Example

\new Staff {

  \set Staff.pedalSustainStyle = #'mixed

  \sustainHalfOn
  b'16 c' d' e'
  \sustainHalfOff
  f'
  \sustainOn
  g' a' a' a' a' a' c'
  \sustainOff
  a' a'
  \sustainOn
  a'
  a'
  \sustainOff\sustainOn
 
  a' a' a' a'
  \sustainOff
  \set Staff.pedalSustainStyle = #'text
  a'
  \sustainHalfOn
  a' a' a' a'
  \sustainHalfOff
  a'
  \sustainOn
  a' a' a' a' a'
  \sustainOff
  a'
}