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git-svn-id: svn://localhost/ardour2/branches/3.0@8101 d708f5d6-7413-0410-9779-e7cbd77b26cf

libs/ardour/ardour/unknown_processor.h

@@ -24,11 +24,27 @@
 
 namespace ARDOUR {
 
+/** A stub Processor that can be used in place of a `real' one that cannot be
+ *  created for some reason; usually because it requires a plugin which is not
+ *  present.  UnknownProcessors are special-cased in a few places, notably
+ *  in route configuration and signal processing, so that on encountering them
+ *  configuration or processing stops.
+ *
+ *  When a Processor is missing from a Route, the following processors cannot
+ *  be configured, as the missing Processor's output port configuration is
+ *  unknown.
+ *
+ *  The main utility of the UnknownProcessor is that it allows state
+ *  to be preserved, so that, for example, loading and re-saving a
+ *  session on a machine without a particular plugin will not corrupt
+ *  the session.
+ */
 class UnknownProcessor : public Processor
 {
 public:
 	UnknownProcessor (Session &, XMLNode const &);
 
+	/* These processors are hidden from view */
 	bool display_to_user () const {
 		return false;
 	}