/*
  thread-devnull-engraver.cc -- implement Thread_devnull_engraver

  source file of the GNU LilyPond music typesetter
  
  (c) 2000--2002 Jan Nieuwenhuizen <janneke@gnu.org>
*/

#include "engraver.hh"
#include "item.hh"
#include "musical-request.hh"
#include "translator-group.hh"

class Thread_devnull_engraver : public Engraver
{
public:
  TRANSLATOR_DECLARATIONS(Thread_devnull_engraver);
  
protected:
  virtual void acknowledge_grob (Grob_info);
};



void
Thread_devnull_engraver::acknowledge_grob (Grob_info i)
{
  SCM s = get_property ("devNullThread");
#if 0
  /* No need, next if will never be true */
  if (s == ly_symbol2scm ("never"))
    return;
#endif

  if (s == ly_symbol2scm ("allways")
      || (s == SCM_EOL
	  && daddy_trans_l_->id_str_.left_str (3) == "two"
	  && (to_boolean (get_property ("unison"))
	      || to_boolean (get_property ("unisilence")))
	  && to_boolean (get_property ("soloADue"))))
    {
      /* Ugh, we can suicide them, but they remain living */
      i.grob_l_->suicide ();
    }
}
Thread_devnull_engraver::Thread_devnull_engraver(){}

ENTER_DESCRIPTION(Thread_devnull_engraver,
/* descr */       "Kill elements whenever we are Voice called `two' and either
unison, unisilence or soloADue is set.@footnote{On unix systems, the
file @file{/dev/null} is special device: anything written to it is
discarded.}. This engraver works closely together with the part
combiner.  When the part combiner notices that two threads are
identical, it tells the @code{Thread_devnull_engraver} to discard
everything in the second thread.
",
/* creats*/       "",
/* acks  */       "grob-interface",
/* reads */       "",
/* write */       "");
