Fix crossfade undo using the stateful diff system. Fixes #3257.

git-svn-id: svn://localhost/ardour2/branches/3.0@7694 d708f5d6-7413-0410-9779-e7cbd77b26cf

21 files changed, 225 insertions, 72 deletions

diff --git a/gtk2_ardour/crossfade_edit.cc b/gtk2_ardour/crossfade_edit.cc
index b6dcf07920..49e5ee0609 100644
--- a/gtk2_ardour/crossfade_edit.cc
+++ b/gtk2_ardour/crossfade_edit.cc
@@ -788,10 +788,10 @@ CrossfadeEditor::apply ()
 	_session->begin_reversible_command (_("Edit crossfade"));
 
 	XMLNode& before = xfade->get_state ();
-
+	
 	_apply_to (xfade);
 
-	_session->add_command (new MementoCommand<Crossfade> (*xfade.get(), &before, &xfade->get_state()));
+	_session->add_command (new MementoCommand<Crossfade> (*xfade.get(), &before, &xfade->get_state ()));
 	_session->commit_reversible_command ();
 }
 
diff --git a/gtk2_ardour/editor_drag.cc b/gtk2_ardour/editor_drag.cc
index f2acf2e7a8..cef27660a6 100644
--- a/gtk2_ardour/editor_drag.cc
+++ b/gtk2_ardour/editor_drag.cc
@@ -1037,6 +1037,15 @@ RegionMoveDrag::finished_no_copy (
 				playlist->freeze ();
 			}
 
+			/* this movement may result in a crossfade being modified, so we need to get undo
+			   data from the playlist as well as the region.
+			*/
+			
+			r = modified_playlists.insert (playlist);
+			if (r.second) {
+				playlist->clear_changes ();
+			}
+
 			rv->region()->set_position (where, (void*) this);
 
 			_editor->session()->add_command (new StatefulDiffCommand (rv->region()));
@@ -1172,7 +1181,12 @@ void
 RegionMoveDrag::add_stateful_diff_commands_for_playlists (PlaylistSet const & playlists)
 {
 	for (PlaylistSet::const_iterator i = playlists.begin(); i != playlists.end(); ++i) {
-		_editor->session()->add_command (new StatefulDiffCommand (*i));
+		StatefulDiffCommand* c = new StatefulDiffCommand (*i);
+		if (!c->empty()) {
+			_editor->session()->add_command (new StatefulDiffCommand (*i));
+		} else {
+			delete c;
+		}
 	}
 }
 
diff --git a/gtk2_ardour/editor_ops.cc b/gtk2_ardour/editor_ops.cc
index f4c63531cc..d540134f17 100644
--- a/gtk2_ardour/editor_ops.cc
+++ b/gtk2_ardour/editor_ops.cc
@@ -2820,11 +2820,9 @@ Editor::separate_regions_between (const TimeSelection& ts)
                                                         
                                                         /* pick up changes to existing regions */
 
-                                                        vector<StatefulDiffCommand*> cmds;
+                                                        vector<Command*> cmds;
                                                         playlist->rdiff (cmds);
-                                                        for (vector<StatefulDiffCommand*>::iterator j = cmds.begin(); j != cmds.end(); ++j) {
-                                                                _session->add_command (*j);
-                                                        }
+							_session->add_commands (cmds);
 
                                                         /* pick up changes to the playlist itself (adds/removes)
                                                          */
@@ -3773,11 +3771,9 @@ Editor::bounce_range_selection (bool replace, bool enable_processing)
 			playlist->add_region (r, start);
 		}
 
-		vector<StatefulDiffCommand*> cmds;
+		vector<Command*> cmds;
 		playlist->rdiff (cmds);
-		for (vector<StatefulDiffCommand*>::iterator j = cmds.begin(); j != cmds.end(); ++j) {
-			_session->add_command (*j);
-		}
+		_session->add_commands (cmds);
 
                 _session->add_command (new StatefulDiffCommand (playlist));
 	}
@@ -4492,13 +4488,10 @@ Editor::nudge_track (bool use_edit, bool forwards)
 
 		playlist->nudge_after (start, distance, forwards);
                 
-                vector<StatefulDiffCommand*> cmds;
+                vector<Command*> cmds;
 
                 playlist->rdiff (cmds);
-
-                for (vector<StatefulDiffCommand*>::iterator c = cmds.begin(); c != cmds.end(); ++c) {
-                        _session->add_command (*c);
-                }
+		_session->add_commands (cmds);
 
                 _session->add_command (new StatefulDiffCommand (playlist));
 	}
@@ -6568,14 +6561,10 @@ Editor::insert_time (nframes64_t pos, nframes64_t frames, InsertTimeOption opt,
 
 			pl->shift (pos, frames, (opt == MoveIntersected), ignore_music_glue);
 
-                        vector<StatefulDiffCommand*> cmds;
-                        
+                        vector<Command*> cmds;
                         pl->rdiff (cmds);
-                        
-                        for (vector<StatefulDiffCommand*>::iterator c = cmds.begin(); c != cmds.end(); ++c) {
-                                _session->add_command (*c);
-                        }
-                        
+			_session->add_commands (cmds);
+			
 			_session->add_command (new StatefulDiffCommand (pl));
 			commit = true;
 		}
diff --git a/gtk2_ardour/route_time_axis.cc b/gtk2_ardour/route_time_axis.cc
index 391b08eac6..abc8101195 100644
--- a/gtk2_ardour/route_time_axis.cc
+++ b/gtk2_ardour/route_time_axis.cc
@@ -1339,13 +1339,10 @@ RouteTimeAxisView::cut_copy_clear (Selection& selection, CutCopyOp op)
 		if ((what_we_got = playlist->cut (time)) != 0) {
 			_editor.get_cut_buffer().add (what_we_got);
 
-                        vector<StatefulDiffCommand*> cmds;
-                        
+                        vector<Command*> cmds;
                         playlist->rdiff (cmds);
-                        
-                        for (vector<StatefulDiffCommand*>::iterator c = cmds.begin(); c != cmds.end(); ++c) {
-                                _session->add_command (*c);
-                        }
+                        _session->add_commands (cmds);
+			
                         _session->add_command (new StatefulDiffCommand (playlist));
 		}
 		break;
@@ -1357,13 +1354,10 @@ RouteTimeAxisView::cut_copy_clear (Selection& selection, CutCopyOp op)
 
 	case Clear:
 		if ((what_we_got = playlist->cut (time)) != 0) {
-                        vector<StatefulDiffCommand*> cmds;
-                        
+
+                        vector<Command*> cmds;
                         playlist->rdiff (cmds);
-                        
-                        for (vector<StatefulDiffCommand*>::iterator c = cmds.begin(); c != cmds.end(); ++c) {
-                                _session->add_command (*c);
-                        }
+			_session->add_commands (cmds);
                         _session->add_command (new StatefulDiffCommand (playlist));
 			what_we_got->release ();
 		}
diff --git a/libs/ardour/ardour/audioplaylist.h b/libs/ardour/ardour/audioplaylist.h
index aee5fb3f64..f2d60bce8b 100644
--- a/libs/ardour/ardour/audioplaylist.h
+++ b/libs/ardour/ardour/audioplaylist.h
@@ -33,12 +33,39 @@ class Region;
 class AudioRegion;
 class Source;
 
+namespace Properties {
+        /* fake the type, since crossfades are handled by SequenceProperty which doesn't
+           care about such things.
+        */
+        extern PBD::PropertyDescriptor<bool> crossfades;
+}
+
+class AudioPlaylist;	
+
+class CrossfadeListProperty : public PBD::SequenceProperty<std::list<boost::shared_ptr<Crossfade> > >
+{
+public:
+	CrossfadeListProperty (AudioPlaylist &);
+
+	void get_content_as_xml (boost::shared_ptr<Crossfade>, XMLNode &) const;
+	boost::shared_ptr<Crossfade> get_content_from_xml (XMLNode const &) const;
+
+private:
+	CrossfadeListProperty* clone () const;
+	CrossfadeListProperty* create () const;
+
+        friend class AudioPlaylist;
+        /* we live and die with our playlist, no lifetime management needed */
+        AudioPlaylist& _playlist;
+};
+
+	
 class AudioPlaylist : public ARDOUR::Playlist
 {
-  public:
+public:
 	typedef std::list<boost::shared_ptr<Crossfade> > Crossfades;
+	static void make_property_quarks ();
 
-   public:
 	AudioPlaylist (Session&, const XMLNode&, bool hidden = false);
 	AudioPlaylist (Session&, std::string name, bool hidden = false);
 	AudioPlaylist (boost::shared_ptr<const AudioPlaylist>, std::string name, bool hidden = false);
@@ -59,6 +86,8 @@ class AudioPlaylist : public ARDOUR::Playlist
 
 	bool destroy_region (boost::shared_ptr<Region>);
 
+	void update (const CrossfadeListProperty::ChangeRecord &);
+
     protected:
 
 	/* playlist "callbacks" */
@@ -72,7 +101,7 @@ class AudioPlaylist : public ARDOUR::Playlist
         void remove_dependents (boost::shared_ptr<Region> region);
 
     private:
-       Crossfades      _crossfades;
+       CrossfadeListProperty _crossfades;
        Crossfades      _pending_xfade_adds;
 
        void crossfade_invalidated (boost::shared_ptr<Region>);
diff --git a/libs/ardour/ardour/crossfade.h b/libs/ardour/ardour/crossfade.h
index 4c75a0226b..2ce504eacf 100644
--- a/libs/ardour/ardour/crossfade.h
+++ b/libs/ardour/ardour/crossfade.h
@@ -73,7 +73,7 @@ class Crossfade : public ARDOUR::AudioRegion
 
 	/* the usual XML constructor */
 
-	Crossfade (const Playlist&, XMLNode&);
+	Crossfade (const Playlist&, XMLNode const &);
 	virtual ~Crossfade();
 
 	static void make_property_quarks ();
diff --git a/libs/ardour/ardour/playlist.h b/libs/ardour/ardour/playlist.h
index 6473211126..a1a7bb752a 100644
--- a/libs/ardour/ardour/playlist.h
+++ b/libs/ardour/ardour/playlist.h
@@ -64,8 +64,8 @@ class RegionListProperty : public PBD::SequenceProperty<std::list<boost::shared_
         RegionListProperty (Playlist&);
 
 	RegionListProperty* clone () const;
-
-        boost::shared_ptr<Region> lookup_id (const PBD::ID& id) const;
+	void get_content_as_xml (boost::shared_ptr<Region>, XMLNode &) const;
+	boost::shared_ptr<Region> get_content_from_xml (XMLNode const &) const;
 
   private:
 	RegionListProperty* create () const;
@@ -90,7 +90,7 @@ public:
 
         void update (const RegionListProperty::ChangeRecord&);
         void clear_owned_changes ();
-        void rdiff (std::vector<PBD::StatefulDiffCommand*>&) const;
+        void rdiff (std::vector<Command*>&) const;
 
 	boost::shared_ptr<Region> region_by_id (const PBD::ID&) const;
 
diff --git a/libs/ardour/ardour/session.h b/libs/ardour/ardour/session.h
index c408714c94..75b9fb1831 100644
--- a/libs/ardour/ardour/session.h
+++ b/libs/ardour/ardour/session.h
@@ -680,6 +680,8 @@ class Session : public PBD::StatefulDestructible, public PBD::ScopedConnectionLi
 		_current_trans.top()->add_command (cmd);
 	}
 
+	void add_commands (std::vector<Command*> const & cmds);
+
 	std::map<PBD::ID,PBD::StatefulDestructible*> registry;
 
 	// these commands are implemented in libs/ardour/session_command.cc
diff --git a/libs/ardour/audio_playlist.cc b/libs/ardour/audio_playlist.cc
index cfc5a4028a..2ac3edff80 100644
--- a/libs/ardour/audio_playlist.cc
+++ b/libs/ardour/audio_playlist.cc
@@ -21,7 +21,6 @@
 
 #include <cstdlib>
 
-
 #include "ardour/types.h"
 #include "ardour/debug.h"
 #include "ardour/configuration.h"
@@ -38,14 +37,70 @@ using namespace ARDOUR;
 using namespace std;
 using namespace PBD;
 
+namespace ARDOUR {
+	namespace Properties {
+		PBD::PropertyDescriptor<bool> crossfades;
+	}
+}
+
+void
+AudioPlaylist::make_property_quarks ()
+{
+        Properties::crossfades.property_id = g_quark_from_static_string (X_("crossfades"));
+        DEBUG_TRACE (DEBUG::Properties, string_compose ("quark for crossfades = %1\n", Properties::crossfades.property_id));
+}
+
+CrossfadeListProperty::CrossfadeListProperty (AudioPlaylist& pl)
+        : SequenceProperty<std::list<boost::shared_ptr<Crossfade> > > (Properties::crossfades.property_id, boost::bind (&AudioPlaylist::update, &pl, _1))
+        , _playlist (pl)
+{
+	
+}
+
+
+CrossfadeListProperty *
+CrossfadeListProperty::create () const
+{
+	return new CrossfadeListProperty (_playlist);
+}
+
+CrossfadeListProperty *
+CrossfadeListProperty::clone () const
+{
+	return new CrossfadeListProperty (*this);
+}
+
+void
+CrossfadeListProperty::get_content_as_xml (boost::shared_ptr<Crossfade> xfade, XMLNode & node) const
+{
+	/* Crossfades are not written to any state when they are no
+	   longer in use, so we must write their state here.
+	*/
+
+	XMLNode& c = xfade->get_state ();
+	node.add_child_nocopy (c);
+}
+
+boost::shared_ptr<Crossfade>
+CrossfadeListProperty::get_content_from_xml (XMLNode const & node) const
+{
+	XMLNodeList const c = node.children ();
+	assert (c.size() == 1);
+	return boost::shared_ptr<Crossfade> (new Crossfade (_playlist, *c.front()));
+}
+
+
 AudioPlaylist::AudioPlaylist (Session& session, const XMLNode& node, bool hidden)
 	: Playlist (session, node, DataType::AUDIO, hidden)
+	, _crossfades (*this)
 {
 #ifndef NDEBUG
 	const XMLProperty* prop = node.property("type");
 	assert(!prop || DataType(prop->value()) == DataType::AUDIO);
 #endif
 
+	add_property (_crossfades);
+
 	in_set_state++;
 	set_state (node, Stateful::loading_state_version);
 	in_set_state--;
@@ -53,12 +108,17 @@ AudioPlaylist::AudioPlaylist (Session& session, const XMLNode& node, bool hidden
 
 AudioPlaylist::AudioPlaylist (Session& session, string name, bool hidden)
 	: Playlist (session, name, DataType::AUDIO, hidden)
+	, _crossfades (*this)
 {
+	add_property (_crossfades);
 }
 
 AudioPlaylist::AudioPlaylist (boost::shared_ptr<const AudioPlaylist> other, string name, bool hidden)
 	: Playlist (other, name, hidden)
+	, _crossfades (*this)
 {
+	add_property (_crossfades);
+	
 	RegionList::const_iterator in_o  = other->regions.begin();
 	RegionList::iterator in_n = regions.begin();
 
@@ -99,7 +159,10 @@ AudioPlaylist::AudioPlaylist (boost::shared_ptr<const AudioPlaylist> other, stri
 
 AudioPlaylist::AudioPlaylist (boost::shared_ptr<const AudioPlaylist> other, nframes_t start, nframes_t cnt, string name, bool hidden)
 	: Playlist (other, start, cnt, name, hidden)
+	, _crossfades (*this)
 {
+	add_property (_crossfades);
+	
 	/* this constructor does NOT notify others (session) */
 }
 
@@ -795,3 +858,13 @@ AudioPlaylist::foreach_crossfade (boost::function<void (boost::shared_ptr<Crossf
 		s (*i);
 	}
 }
+
+void
+AudioPlaylist::update (const CrossfadeListProperty::ChangeRecord& change)
+{
+	for (CrossfadeListProperty::ChangeContainer::const_iterator i = change.added.begin(); i != change.added.end(); ++i) {
+		add_crossfade (*i);
+	}
+
+	/* don't remove crossfades here; they will be dealt with by the dependency code */
+}
diff --git a/libs/ardour/crossfade.cc b/libs/ardour/crossfade.cc
index 601ea86f6b..eb1148fa2c 100644
--- a/libs/ardour/crossfade.cc
+++ b/libs/ardour/crossfade.cc
@@ -124,7 +124,7 @@ Crossfade::Crossfade (boost::shared_ptr<AudioRegion> a, boost::shared_ptr<AudioR
 	initialize ();
 }
 
-Crossfade::Crossfade (const Playlist& playlist, XMLNode& node)
+Crossfade::Crossfade (const Playlist& playlist, XMLNode const & node)
 	: AudioRegion (playlist.session(), 0, 0, "unnamed crossfade")
 	, CROSSFADE_DEFAULT_PROPERTIES
 	, _fade_in (Evoral::Parameter(FadeInAutomation)) // linear (gain coefficient) => -inf..+6dB
@@ -132,7 +132,7 @@ Crossfade::Crossfade (const Playlist& playlist, XMLNode& node)
 
 {
 	boost::shared_ptr<Region> r;
-	XMLProperty* prop;
+	XMLProperty const * prop;
 	LocaleGuard lg (X_("POSIX"));
 
 	/* we have to find the in/out regions before we can do anything else */
diff --git a/libs/ardour/globals.cc b/libs/ardour/globals.cc
index 2ecea550b5..0e12883d82 100644
--- a/libs/ardour/globals.cc
+++ b/libs/ardour/globals.cc
@@ -69,7 +69,7 @@
 #include "ardour/debug.h"
 #include "ardour/filesystem_paths.h"
 #include "ardour/mix.h"
-#include "ardour/playlist.h"
+#include "ardour/audioplaylist.h"
 #include "ardour/plugin_manager.h"
 #include "ardour/process_thread.h"
 #include "ardour/profile.h"
@@ -251,6 +251,7 @@ ARDOUR::init (bool use_vst, bool try_optimization)
 	AudioRegion::make_property_quarks ();
 	RouteGroup::make_property_quarks ();
         Playlist::make_property_quarks ();
+        AudioPlaylist::make_property_quarks ();
 
 	/* this is a useful ready to use PropertyChange that many
 	   things need to check. This avoids having to compose
diff --git a/libs/ardour/playlist.cc b/libs/ardour/playlist.cc
index 93a4d520e8..1b2d64baba 100644
--- a/libs/ardour/playlist.cc
+++ b/libs/ardour/playlist.cc
@@ -110,28 +110,46 @@ RegionListProperty::RegionListProperty (Playlist& pl)
         : SequenceProperty<std::list<boost::shared_ptr<Region> > > (Properties::regions.property_id, boost::bind (&Playlist::update, &pl, _1))
         , _playlist (pl)
 {
+	
 }
 
-boost::shared_ptr<Region>
-RegionListProperty::lookup_id (const ID& id) const
+RegionListProperty *
+RegionListProperty::clone () const
 {
-        boost::shared_ptr<Region> ret =  _playlist.region_by_id (id);
-        
-        if (!ret) {
-                ret = RegionFactory::region_by_id (id);
-        }
+	return new RegionListProperty (*this);
+}
 
-        return ret;
+RegionListProperty *
+RegionListProperty::create () const
+{
+	return new RegionListProperty (_playlist);
 }
 
-RegionListProperty* RegionListProperty::clone () const
+void
+RegionListProperty::get_content_as_xml (boost::shared_ptr<Region> region, XMLNode & node) const
 {
-	return new RegionListProperty (*this);
+	/* All regions (even those which are deleted) have their state saved by other
+	   code, so we can just store ID here.
+	*/
+	
+	node.add_property ("id", region->id().to_s ());
 }
 
-RegionListProperty* RegionListProperty::create () const
+boost::shared_ptr<Region>
+RegionListProperty::get_content_from_xml (XMLNode const & node) const
 {
-	return new RegionListProperty (_playlist);
+	XMLProperty const * prop = node.property ("id");
+	assert (prop);
+
+	PBD::ID id (prop->value ());
+
+        boost::shared_ptr<Region> ret = _playlist.region_by_id (id);
+        
+        if (!ret) {
+                ret = RegionFactory::region_by_id (id);
+        }
+
+        return ret;
 }
 
 Playlist::Playlist (Session& sess, string nom, DataType type, bool hide)
@@ -2100,7 +2118,7 @@ Playlist::mark_session_dirty ()
 }
 
 void
-Playlist::rdiff (vector<StatefulDiffCommand*>& cmds) const
+Playlist::rdiff (vector<Command*>& cmds) const
 {
 	RegionLock rlock (const_cast<Playlist *> (this));
 	Stateful::rdiff (cmds);
diff --git a/libs/ardour/session_state.cc b/libs/ardour/session_state.cc
index 31282a210f..225b7c1909 100644
--- a/libs/ardour/session_state.cc
+++ b/libs/ardour/session_state.cc
@@ -2313,6 +2313,14 @@ Session::finish_reversible_command (UndoTransaction& ut)
 }
 
 void
+Session::add_commands (vector<Command*> const & cmds)
+{
+	for (vector<Command*>::const_iterator i = cmds.begin(); i != cmds.end(); ++i) {
+		add_command (*i);
+	}
+}
+
+void
 Session::begin_reversible_command(const string& name)
 {
 	UndoTransaction* trans = new UndoTransaction();
diff --git a/libs/ardour/wscript b/libs/ardour/wscript
index 051054c9a7..f877f3c3be 100644
--- a/libs/ardour/wscript
+++ b/libs/ardour/wscript
@@ -286,7 +286,7 @@ def build(bld):
 	obj.includes     = ['.', '../surfaces/control_protocol', '..']
 	obj.name         = 'libardour'
 	obj.target       = 'ardour'
-	obj.uselib       = 'GLIBMM GTHREAD AUBIO SIGCPP XML UUID JACK SNDFILE SAMPLERATE LRDF OSX COREAUDIO'
+	obj.uselib       = 'GLIBMM GTHREAD AUBIO SIGCPP XML UUID JACK SNDFILE SAMPLERATE LRDF OSX COREAUDIO CURL DL'
 	obj.uselib_local = 'libpbd libmidipp libevoral libvamphost libvampplugin libtaglib librubberband libaudiographer'
 	obj.vnum         = LIBARDOUR_LIB_VERSION
 	obj.install_path = os.path.join(bld.env['LIBDIR'], 'ardour3')
diff --git a/libs/pbd/pbd/command.h b/libs/pbd/pbd/command.h
index c6c3c8d3fd..db4d2bbd81 100644
--- a/libs/pbd/pbd/command.h
+++ b/libs/pbd/pbd/command.h
@@ -43,6 +43,10 @@ public:
 	virtual XMLNode &get_state();
 	virtual int set_state(const XMLNode&, int /*version*/) { /* noop */ return 0; }
 
+	virtual bool empty () const {
+		return false;
+	}
+
 protected:
 	Command() {}
 	Command(const std::string& name) : _name(name) {}
diff --git a/libs/pbd/pbd/property_basics.h b/libs/pbd/pbd/property_basics.h
index cfae36df20..145e84abfc 100644
--- a/libs/pbd/pbd/property_basics.h
+++ b/libs/pbd/pbd/property_basics.h
@@ -103,7 +103,7 @@ public:
 	virtual void get_changes_as_properties (PropertyList& changes, Command *) const = 0;
 
 	/** Collect StatefulDiffCommands for changes to anything that we own */
-	virtual void rdiff (std::vector<StatefulDiffCommand*> &) const {}
+	virtual void rdiff (std::vector<Command*> &) const {}
 
 	/** Look in an XML node written by get_changes_as_xml and, if XML from this property
 	 *  is found, create a property with the changes from the XML.
diff --git a/libs/pbd/pbd/sequence_property.h b/libs/pbd/pbd/sequence_property.h
index 5b37d7a0fc..4b494d4a8d 100644
--- a/libs/pbd/pbd/sequence_property.h
+++ b/libs/pbd/pbd/sequence_property.h
@@ -31,6 +31,7 @@
 #include "pbd/id.h"
 #include "pbd/property_basics.h"
 #include "pbd/property_list.h"
+#include "pbd/stateful_diff_command.h"
 
 namespace PBD {
 
@@ -80,8 +81,6 @@ class SequenceProperty : public PropertyBase
 	SequenceProperty (PropertyID id, const boost::function<void(const ChangeRecord&)>& update)
                 : PropertyBase (id), _update_callback (update) {}
 
-	virtual typename Container::value_type lookup_id (const PBD::ID&) const = 0;
-
         void invert () {
 		_changes.removed.swap (_changes.added);
         }
@@ -97,18 +96,25 @@ class SequenceProperty : public PropertyBase
 			for (typename ChangeContainer::iterator i = _changes.added.begin(); i != _changes.added.end(); ++i) {
                                 XMLNode* add_node = new XMLNode ("Add");
                                 child->add_child_nocopy (*add_node);
-                                add_node->add_property ("id", (*i)->id().to_s());
+				get_content_as_xml (*i, *add_node);
 			}
 		}
 		if (!_changes.removed.empty()) {
 			for (typename ChangeContainer::iterator i = _changes.removed.begin(); i != _changes.removed.end(); ++i) {
                                 XMLNode* remove_node = new XMLNode ("Remove");
                                 child->add_child_nocopy (*remove_node);
-                                remove_node->add_property ("id", (*i)->id().to_s());
+				get_content_as_xml (*i, *remove_node);
 			}
 		}
 	}
 
+	/** Get a representation of one of our items as XML.  The representation must be sufficient to
+	 *  restore the item's state later; an ID is ok if someone else is storing the item state,
+	 *  otherwise it needs to be the full state.  The supplied node is an <Add> or <Remove>
+	 *  which this method can either add properties or children to.
+	 */
+	virtual void get_content_as_xml (typename ChangeContainer::value_type, XMLNode &) const = 0;
+
 	bool set_value (XMLNode const &) {
 		/* XXX: not used, but probably should be */
 		assert (false);
@@ -191,11 +197,10 @@ class SequenceProperty : public PropertyBase
 
 		XMLNodeList const & grandchildren = (*i)->children ();
 		for (XMLNodeList::const_iterator j = grandchildren.begin(); j != grandchildren.end(); ++j) {
-			XMLProperty const * prop = (*j)->property ("id");
-			assert (prop);
-			PBD::ID id (prop->value ());
-			typename Container::value_type v = lookup_id (id);
+
+			typename Container::value_type v = get_content_from_xml (**j);
 			assert (v);
+			
 			if ((*j)->name() == "Add") {
 				p->_changes.added.insert (v);
 			} else if ((*j)->name() == "Remove") {
@@ -206,13 +211,16 @@ class SequenceProperty : public PropertyBase
 		return p;
         }
 
+	/** Given an <Add> or <Remove> node as passed into get_content_to_xml, obtain an item */
+	virtual typename Container::value_type get_content_from_xml (XMLNode const & node) const = 0;
+
 	void clear_owned_changes () {
 		for (typename Container::iterator i = begin(); i != end(); ++i) {
 			(*i)->clear_changes ();
 		}
 	}
 
-	void rdiff (std::vector<StatefulDiffCommand*>& cmds) const {
+	void rdiff (std::vector<Command*>& cmds) const {
 		for (typename Container::const_iterator i = begin(); i != end(); ++i) {
 			if ((*i)->changed ()) {
 				StatefulDiffCommand* sdc = new StatefulDiffCommand (*i);
@@ -255,6 +263,11 @@ class SequenceProperty : public PropertyBase
 		return _val.erase (f, l);
 	}
 
+	void remove (const typename Container::value_type& v) {
+		_changes.remove (v);
+		_val.remove (v);
+	}
+
 	void push_back (const typename Container::value_type& v) {
 		_changes.add (v);
 		_val.push_back (v);
diff --git a/libs/pbd/pbd/stateful.h b/libs/pbd/pbd/stateful.h
index 5c1f079bc6..735ffbdc4a 100644
--- a/libs/pbd/pbd/stateful.h
+++ b/libs/pbd/pbd/stateful.h
@@ -70,7 +70,7 @@ class Stateful {
 	void clear_changes ();
 	virtual void clear_owned_changes ();
         PropertyList* get_changes_as_properties (Command *) const;
-	virtual void rdiff (std::vector<StatefulDiffCommand*> &) const;
+	virtual void rdiff (std::vector<Command*> &) const;
         bool changed() const;
 
         /* create a property list from an XMLNode
diff --git a/libs/pbd/pbd/stateful_diff_command.h b/libs/pbd/pbd/stateful_diff_command.h
index 2d5c234d76..2a213d7a17 100644
--- a/libs/pbd/pbd/stateful_diff_command.h
+++ b/libs/pbd/pbd/stateful_diff_command.h
@@ -45,6 +45,8 @@ public:
         
 	XMLNode& get_state ();
 
+	bool empty () const;
+
 private:
 	boost::weak_ptr<Stateful> _object; ///< the object in question
         PBD::PropertyList* _changes; ///< property changes to execute this command
diff --git a/libs/pbd/stateful.cc b/libs/pbd/stateful.cc
index 8411dc4e60..e13a499e41 100644
--- a/libs/pbd/stateful.cc
+++ b/libs/pbd/stateful.cc
@@ -340,7 +340,7 @@ Stateful::property_factory (const XMLNode& history_node) const
 }
 
 void
-Stateful::rdiff (vector<StatefulDiffCommand*>& cmds) const
+Stateful::rdiff (vector<Command*>& cmds) const
 {
 	for (OwnedPropertyList::const_iterator i = _properties->begin(); i != _properties->end(); ++i) {
 		i->second->rdiff (cmds);
diff --git a/libs/pbd/stateful_diff_command.cc b/libs/pbd/stateful_diff_command.cc
index 93a215ad8a..0f456d2d6e 100644
--- a/libs/pbd/stateful_diff_command.cc
+++ b/libs/pbd/stateful_diff_command.cc
@@ -118,3 +118,9 @@ StatefulDiffCommand::get_state ()
 
 	return *node;
 }
+
+bool
+StatefulDiffCommand::empty () const
+{
+	return _changes->empty();
+}