Use a MementoCommandBinder for Crossfades so that the undo record can contain details for crossfades that are subsequently deleted (#4325).

git-svn-id: svn://localhost/ardour2/branches/3.0@10104 d708f5d6-7413-0410-9779-e7cbd77b26cf

5 files changed, 34 insertions, 15 deletions

diff --git a/libs/ardour/ardour/midi_automation_list_binder.h b/libs/ardour/ardour/midi_automation_list_binder.h
index 95576b47de..89c6cdb90b 100644
--- a/libs/ardour/ardour/midi_automation_list_binder.h
+++ b/libs/ardour/ardour/midi_automation_list_binder.h
@@ -33,7 +33,7 @@ public:
 	MidiAutomationListBinder (boost::shared_ptr<ARDOUR::MidiSource>, Evoral::Parameter);
 	MidiAutomationListBinder (XMLNode *, ARDOUR::Session::SourceMap const &);
 
-	ARDOUR::AutomationList* get ();
+	ARDOUR::AutomationList* get () const;
 	void add_state (XMLNode *);
 
 private:
diff --git a/libs/ardour/midi_automation_list_binder.cc b/libs/ardour/midi_automation_list_binder.cc
index 0f8e4884ca..fbb87c5cfa 100644
--- a/libs/ardour/midi_automation_list_binder.cc
+++ b/libs/ardour/midi_automation_list_binder.cc
@@ -49,7 +49,7 @@ MidiAutomationListBinder::MidiAutomationListBinder (XMLNode* node, Session::Sour
 }
 
 AutomationList*
-MidiAutomationListBinder::get ()
+MidiAutomationListBinder::get () const
 {
 	boost::shared_ptr<MidiModel> model = _source->model ();
 	assert (model);
diff --git a/libs/ardour/session_command.cc b/libs/ardour/session_command.cc
index c240a4aa94..e5ddd0a097 100644
--- a/libs/ardour/session_command.cc
+++ b/libs/ardour/session_command.cc
@@ -34,6 +34,7 @@
 #include "ardour/session_playlists.h"
 #include "ardour/region_factory.h"
 #include "ardour/midi_automation_list_binder.h"
+#include "ardour/crossfade_binder.h"
 #include "ardour/crossfade.h"
 #include "pbd/error.h"
 #include "pbd/id.h"
@@ -143,11 +144,16 @@ Session::memento_command_factory(XMLNode *n)
 	    cerr << "Alist " << id << " not found\n";
 
     } else if (obj_T == "ARDOUR::Crossfade") {
-	    boost::shared_ptr<Crossfade> c = playlists->find_crossfade (id);
-	    if (c) {
-		    return new MementoCommand<Crossfade> (*c.get(), before, after);
+	    if (have_id) {
+		    boost::shared_ptr<Crossfade> c = playlists->find_crossfade (id);
+		    if (c) {
+			    return new MementoCommand<Crossfade> (*c.get(), before, after);
+		    }
 	    } else {
-		    error << string_compose (X_("Crossfade %1 not found in session"), id) << endmsg;
+		    return new MementoCommand<Crossfade> (
+			    new CrossfadeBinder (n, playlists),
+			    before, after
+			    );
 	    }
 
     } else if (registry.count(id)) { // For Editor and AutomationLine which are off-limits herea
diff --git a/libs/ardour/wscript b/libs/ardour/wscript
index b347e73e7e..1b71f58298 100644
--- a/libs/ardour/wscript
+++ b/libs/ardour/wscript
@@ -71,6 +71,7 @@ libardour_sources = [
         'control_protocol_manager.cc',
         'control_protocol_search_path.cc',
         'crossfade.cc',
+        'crossfade_binder.cc',
         'cycle_timer.cc',
         'data_type.cc',
         'default_click.cc',
diff --git a/libs/pbd/pbd/memento_command.h b/libs/pbd/pbd/memento_command.h
index 8b412937ef..45cb100a36 100644
--- a/libs/pbd/pbd/memento_command.h
+++ b/libs/pbd/pbd/memento_command.h
@@ -34,20 +34,32 @@
 /** A class that can return a Stateful object which is the subject of a MementoCommand.
  *
  *  The existence of this class means that the undo record can refer to objects which
- *  don't exist in the session file.  Currently this is just used for MIDI automation;
- *  when MIDI automation is edited, undo records are written for the AutomationList being
- *  changed.  However this AutomationList is a temporary structure, built by a MidiModel,
- *  which doesn't get written to the session file.  Hence we need to be able to go from
- *  a MidiSource and Parameter to an AutomationList.  This Binder mechanism allows this
- *  through MidiAutomationListBinder; the undo record stores the source and parameter,
+ *  don't exist in the session file.  Currently this is used for
+ *
+ *  1.  MIDI automation; when MIDI automation is edited, undo records are
+ *  written for the AutomationList being changed.  However this AutomationList
+ *  is a temporary structure, built by a MidiModel, which doesn't get written
+ *  to the session file.  Hence we need to be able to go from a MidiSource and
+ *  Parameter to an AutomationList.  This Binder mechanism allows this through
+ *  MidiAutomationListBinder; the undo record stores the source and parameter,
  *  and these are bound to an AutomationList by the Binder.
+ *
+ *  2.  Crossfades; unlike regions, these are completely removed from a session
+ *  when they are deleted.  This means that the undo record can contain
+ *  references to non-existant crossfades.  To get around this, CrossfadeBinder
+ *  can do `just-in-time' binding from the crossfade ID.
  */
 template <class obj_T>
 class MementoCommandBinder : public PBD::Destructible
 {
 public:
 	/** @return Stateful object to operate on */
-	virtual obj_T* get () = 0;
+	virtual obj_T* get () const = 0;
+
+	/** @return Name of our type */
+	virtual std::string type_name () const {
+		return PBD::demangled_name (*get ());
+	}
 
 	/** Add our own state to an XMLNode */
 	virtual void add_state (XMLNode *) = 0;
@@ -64,7 +76,7 @@ public:
 		_object.Destroyed.connect_same_thread (_object_death_connection, boost::bind (&SimpleMementoCommandBinder::object_died, this));
 	}
 
-	obj_T* get () {
+	obj_T* get () const {
 		return &_object;
 	}
 
@@ -140,7 +152,7 @@ public:
 		XMLNode* node = new XMLNode(name);
 		_binder->add_state (node);
 		
-		node->add_property("type_name", demangled_name (*_binder->get()));
+		node->add_property ("type_name", _binder->type_name ());
 
 		if (before) {
 			node->add_child_copy(*before);