+
+class Grace_auto_beam_engraver : public Auto_beam_engraver
+{
+ TRANSLATOR_DECLARATIONS (Grace_auto_beam_engraver);
+ TRANSLATOR_INHERIT (Auto_beam_engraver);
+
+private:
+ Moment last_grace_start_; // Full starting time of last grace group
+ Moment last_grace_position_; // Measure position of same
+ virtual void process_music ();
+ virtual bool is_same_grace_state (Moment, Moment);
+ virtual bool test_moment (Direction, Moment, Moment);
+};
+
+Grace_auto_beam_engraver::Grace_auto_beam_engraver (Context *c)
+ : Auto_beam_engraver (c)
+{
+ last_grace_start_.main_part_.set_infinite (-1);
+ // grace_part_ is zero -> test_moment is false, last_grace_position_
+ // not considered.
+}
+
+bool
+Grace_auto_beam_engraver::is_same_grace_state (Moment, Moment)
+{
+ // This is for ignoring interspersed grace notes in main note
+ // beaming. We never want to ignore something inside of grace note
+ // beaming, so return true.
+ return true;
+}
+
+void
+Grace_auto_beam_engraver::process_music ()
+{
+ Moment now = now_mom ();
+ // Update last_grace_start_ and last_grace_position_ only when the
+ // main time advances.
+ if (now.main_part_ > last_grace_start_.main_part_)
+ {
+ last_grace_start_ = now;
+ last_grace_position_ = measure_position (context ());
+ }
+
+ Auto_beam_engraver::process_music ();
+}
+
+bool
+Grace_auto_beam_engraver::test_moment (Direction dir, Moment test_mom, Moment)
+{
+ // If no grace group started this main moment, we have no business
+ // beaming. Same if we have left the original main time step.
+ if (!last_grace_start_.grace_part_
+ || last_grace_position_.main_part_ != test_mom.main_part_)
+ return false;
+ // Autobeam start only when at the start of the grace group.
+ if (dir == START)
+ return last_grace_position_ == test_mom;
+ // Autobeam end only when the grace part is finished.
+ return !test_mom.grace_part_;
+}
+
+void
+Grace_auto_beam_engraver::boot ()
+{
+ ADD_LISTENER (Grace_auto_beam_engraver, beam_forbid);
+ ADD_ACKNOWLEDGER (Grace_auto_beam_engraver, stem);
+ ADD_ACKNOWLEDGER (Grace_auto_beam_engraver, bar_line);
+ ADD_ACKNOWLEDGER (Grace_auto_beam_engraver, beam);
+ ADD_ACKNOWLEDGER (Grace_auto_beam_engraver, breathing_sign);
+ ADD_ACKNOWLEDGER (Grace_auto_beam_engraver, rest);
+}
+
+ADD_TRANSLATOR (Grace_auto_beam_engraver,
+ /* doc */
+ "Generates one autobeam group across an entire grace phrase. "
+ " As usual, any manual beaming or @code{\\noBeam} will block"
+ " autobeaming, just like setting the context property"
+ " @samp{autoBeaming} to @code{##f}.",
+
+ /* create */
+ "Beam ",
+
+ /* read */
+ "autoBeaming ",
+
+ /* write */
+ ""
+ );