From 6a023cc84879573668eaf9120bb13b93cfdf12cb Mon Sep 17 00:00:00 2001
From: David Kastrup <dak@gnu.org>
Date: Thu, 2 Oct 2014 16:13:51 +0200
Subject: [PATCH] Issue 630/3: Let Grace_iterator produce a GraceChange event

---
 lily/grace-iterator.cc         | 11 ++++++++++-
 lily/include/grace-iterator.hh |  2 ++
 scm/define-event-classes.scm   |  2 +-
 3 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/lily/grace-iterator.cc b/lily/grace-iterator.cc
index c0c6c6ec2c..97920b06e6 100644
--- a/lily/grace-iterator.cc
+++ b/lily/grace-iterator.cc
@@ -19,13 +19,22 @@
 
 #include "grace-iterator.hh"
 #include "global-context.hh"
-#include "warn.hh"
+#include "music.hh"
 
 void
 Grace_iterator::process (Moment m)
 {
   Moment main;
   main.main_part_ = -start_mom_.grace_part_ + m.grace_part_;
+
+  // GraceChange is announced in order to make the Grace_engraver able
+  // to distinguish \stemNeutral \grace { ... and \grace { \stemNeutral ...
+  if (in_grace_ != bool (m.grace_part_) && child_iter_ && child_iter_->get_outlet ())
+    {
+      send_stream_event (child_iter_->get_outlet (), "GraceChange", get_music ()->origin (), 0);
+    }
+  in_grace_ = m.grace_part_;
+
   Music_wrapper_iterator::process (main);
 
   /* We can safely do this, since \grace should always be inside
diff --git a/lily/include/grace-iterator.hh b/lily/include/grace-iterator.hh
index 4da3511c0b..4718adf0be 100644
--- a/lily/include/grace-iterator.hh
+++ b/lily/include/grace-iterator.hh
@@ -24,7 +24,9 @@
 
 class Grace_iterator : public Music_wrapper_iterator
 {
+  bool in_grace_;
 public:
+  Grace_iterator() : in_grace_ (false) { }
   virtual void process (Moment);
   DECLARE_SCHEME_CALLBACK (constructor, ());
   DECLARE_CLASSNAME (Grace_iterator);
diff --git a/scm/define-event-classes.scm b/scm/define-event-classes.scm
index b568945081..9e1f4e5936 100644
--- a/scm/define-event-classes.scm
+++ b/scm/define-event-classes.scm
@@ -25,7 +25,7 @@
                  (RemoveContext
                   ChangeParent Override Revert UnsetProperty SetProperty
                   music-event OldMusicEvent CreateContext Prepare
-                  OneTimeStep Finish))
+                  OneTimeStep Finish GraceChange))
     (music-event . (annotate-output-event
                     footnote-event arpeggio-event breathing-event
                     extender-event span-event rhythmic-event dynamic-event
-- 
2.39.5