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10.11.5 Acknowledging grobs

Some engravers also need information from grobs as they are created and as they terminate. The mechanism and methods to obtain this information are set up by the macros:

• DECLARE_ACKNOWLEDGER (grob_interface)
• DECLARE_END_ACKNOWLEDGER (grob_interface)

where grob_interface is an interface supported by the grob(s) which should be acknowledged. For example, the following code would declare acknowledgers for a NoteHead grob (via the note-head-interface) and any grobs which support the side-position-interface:

DECLARE_ACKNOWLEDGER (note_head)
DECLARE_ACKNOWLEDGER (side_position)

The DECLARE_END_ACKNOWLEDGER () macro sets up a spanner-specific acknowledger which will be called whenever a spanner ends.

Following declaration of an acknowledger, the method is coded as follows:

void
Engraver_name::acknowledge_interface_name (Grob_info info)
{
  ...body of acknowledger method...
}

Acknowledge functions are called in the order engravers are \consist-ed (the only exception is if you set must-be-last to #t).

If useful things are to be done to the acknowledged grobs, this should be deferred until all the acknowledging has finished, i.e., store the acknowledged grobs and process the information in a process-acknowledged () or stop-translation-timestep () function.

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LilyPond — Contributor’s Guide v2.18.2 (stable-branch).