Modify Stateful to allow undo to be done using differences in state.

git-svn-id: svn://localhost/ardour2/branches/3.0@6664 d708f5d6-7413-0410-9779-e7cbd77b26cf

1 files changed, 31 insertions, 0 deletions

diff --git a/libs/pbd/stateful.cc b/libs/pbd/stateful.cc
index 596402576e..9f510b85d4 100644
--- a/libs/pbd/stateful.cc
+++ b/libs/pbd/stateful.cc
@@ -47,6 +47,10 @@ Stateful::~Stateful ()
 	// means it needs to live on indefinately.
 
 	delete _instant_xml;
+
+	for (list<StateBase*>::iterator i = _states.begin(); i != _states.end(); ++i) {
+		delete *i;
+	}
 }
 
 void
@@ -149,4 +153,31 @@ Stateful::instant_xml (const string& str, const sys::path& directory_path)
 	return 0;
 }
 
+/** Forget about any old state for this object */	
+void
+Stateful::clear_history ()
+{
+	for (list<StateBase*>::iterator i = _states.begin(); i != _states.end(); ++i) {
+		(*i)->clear_history ();
+	}
+}
+
+/** @return A pair of XMLNodes representing state that has changed since the last time clear_history
+ *  was called on this object; the first is the state before, the second the state after.
+ *
+ *  It is the caller's responsibility to delete the returned XMLNodes.
+ */
+pair<XMLNode *, XMLNode *>
+Stateful::diff ()
+{
+	XMLNode* old = new XMLNode (_xml_node_name);
+	XMLNode* current = new XMLNode (_xml_node_name);
+
+	for (list<StateBase*>::iterator i = _states.begin(); i != _states.end(); ++i) {
+		(*i)->diff (old, current);
+	}
+
+	return make_pair (old, current);
+}
+
 } // namespace PBD