4.17.3 Applyoutput

The most versatile way of tuning an object is \applyoutput. Its syntax is

     \applyoutput proc

where proc is a Scheme function, taking three arguments.

When interpreted, the function proc is called for every layout object found in the context, with the following arguments:

• the layout object itself,
• the context where the layout object was created, and
• the context where \applyoutput is processed.

In addition, the cause of the layout object, i.e. the music expression or object that was responsible for creating it, is in the object property cause. For example, for a note head, this is a NoteHead (lilypond-internals) event, and for a Stem (lilypond-internals) object, this is a NoteHead (lilypond-internals) object.

Here is a simple example of \applyoutput; it blanks note-heads on the center-line:

     (define (blanker grob grob-origin context)
       (if (and (memq (ly:get-grob-property grob 'interfaces)
                      note-head-interface)
                (eq? (ly:get-grob-property grob 'staff-position) 0))
     
                (ly:set-grob-property! grob 'transparent #t)))

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