12.5.2 Running a function on all layout objects

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

\applyOutput context 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 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 event, and for a Stem object, this is a NoteHead object.

Here is a function to use for \applyOutput; it blanks note-heads on the center-line:

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