Mixer: Refuse to bypass modules whose channel configuration makes bypassing illogical.

mixer/src/Module.C

@@ -700,7 +700,14 @@ Module::menu_cb ( const Fl_Menu_ *m )
     if ( ! strcmp( picked, "Edit Parameters" ) )
         command_open_parameter_editor();
     else if ( ! strcmp( picked, "Bypass" ) )
-        bypass( ! ( m->mvalue()->flags & FL_MENU_VALUE ) );
+        if ( ! bypassable() )
+        {
+            fl_alert( "Due to its channel configuration, this module cannot be bypassed." );
+        }
+        else
+        {
+            bypass( ! ( m->mvalue()->flags & FL_MENU_VALUE ) );
+        }
     else if ( ! strcmp( picked, "Cut" ) )
     {
         copy();
@@ -818,8 +825,15 @@ Module::handle ( int m )
             }
             else if ( test_press( FL_BUTTON2 ) )
             {
-                bypass( !bypass() );
-                redraw();
+                if ( !bypassable() )
+                {
+                    fl_alert( "Due to its channel configuration, this module cannot be bypassed." );
+                }
+                else
+                {
+                    bypass( !bypass() );
+                    redraw();
+                }
                 return 1;
             }
 

mixer/src/Module.H

@@ -354,6 +354,12 @@ public:
     virtual bool bypass ( void ) const { return _bypass; }
     virtual void bypass ( bool v ) { _bypass = v; redraw(); }
 
+    virtual bool bypassable ( void ) const
+        {
+            return ninputs() == noutputs() ||
+                ( ninputs() == 1 && noutputs() == 2 );            
+        }
+
     int control_input_port_index ( Port *p )
         {
             for ( nframes_t i = control_input.size(); i--; )