Try to use part of FLTK's DND system for inter-track region dragging.

Audio_Track.C

@@ -55,18 +55,24 @@ Audio_Track::handle ( int m )
 {
     switch ( m )
     {
+
        case FL_DND_DRAG:
-        case FL_DND_ENTER:
-        case FL_ENTER:
-//                    dump();
-            return 1;
-        case FL_DND_LEAVE:
+           return Track::handle( m ) | 1;
+
+/*         case FL_DND_ENTER: */
+/*         case FL_DND_LEAVE: */
+
         case FL_DND_RELEASE:
             return 1;
+
         case FL_PASTE:
         {
             const char *text = Fl::event_text();
 
+
+            if ( ! strcmp( text, "Region" ) )
+                 return 0;
+
             char *file;
 
             if ( ! sscanf( text, "file://%a[^\r\n]\n", &file ) )

Audio_Track.H

@@ -33,6 +33,8 @@ public:
         {
         }
 
+    const char *class_name ( void ) { return "Audio_Track"; }
+
     int handle ( int m );
     void dump ( void );
     void remove_selected ( void );

Control_Track.H

@@ -27,11 +27,14 @@ class Control_Track : public Track
 
 public:
 
+
     Control_Track ( int X, int Y, int W, int H ) : Track( X, Y, W, H )
         {
             color( fl_darker( FL_GREEN ) );
         }
 
+    const char *class_name ( void ) { return "Control_Track"; }
+
     void
     draw ( void )
         {

Region.C

@@ -380,16 +380,14 @@ Region::handle ( int m )
             {
                 if ( Y > y() + h() )
                 {
-                    if ( _track->next() )
-                        if ( Y > _track->next()->y() )
-                            _track->next()->add( this );
+                    Fl::copy( class_name(), strlen( class_name() ), 0 );
+                    Fl::dnd();
                 }
                 else
                     if ( Y < y() )
                     {
-                        if ( _track->prev() )
-                            if ( Y < _track->prev()->y() + _track->prev()->h() )
-                                _track->prev()->add( this );
+                        Fl::copy( class_name(), strlen( class_name() ), 0 );
+                        Fl::dnd();
                     }
             }
 

Timeline.C

@@ -151,17 +151,11 @@ Timeline::Timeline ( int X, int Y, int W, int H, const char* L ) : Fl_Overlay_Wi
             o->type( Fl_Pack::VERTICAL );
             o->spacing( 0 );
 
-            Track *l = NULL;
             for ( int i = 8; i--;  )
             {
 //                Track_Header *t = new Track_Header( 0, 0, W, 75 );
                 Track_Header *t = new Track_Header( 0, 0, W, 30 );
                 Track *o = new Audio_Track( 0, 0, 1, 100 );
-                o->prev( l );
-                if ( l )
-                    l->next( o );
-                l = o;
-//                o->end();
 
                 t->track( o );
                 t->add( new Audio_Track( 0, 0, 1, 100 ) );

Track.C

@@ -26,6 +26,7 @@
 
 
 queue <Track_Widget *> Track::_delete_queue;
+Track_Widget *Track::pushed = NULL;
 
 void
 Track::sort ( void )
@@ -240,17 +241,23 @@ done:
 int
 Track::handle ( int m )
 {
-    static Track_Widget *pushed;
+//    static Track_Widget *pushed;
     static Track_Widget *belowmouse;
 
     switch ( m )
     {
-        case FL_ENTER:
-        case FL_LEAVE:
+        case FL_DND_ENTER:
+            printf( "enter\n" );
+            if ( pushed && pushed->track()->class_name() == class_name() )
+            {
+                printf( "%s -> %s\n", pushed->track()->class_name(), class_name() );
+                add( pushed );
+                redraw();
+            }
+        case FL_DND_LEAVE:
             return 1;
         case FL_MOVE:
         {
-            /* these aren't used, so don't bother doing lookups for them */
             Track_Widget *r = event_widget();
 
             if ( r != belowmouse )
@@ -263,7 +270,7 @@ Track::handle ( int m )
                     r->handle( FL_ENTER );
             }
 
-            return 1;
+            return 0;
         }
         default:
         {

Track.H

@@ -38,18 +38,18 @@ class Track_Widget;
 
 class Track : public Fl_Group, public Loggable
 {
-    Track *_next;
-    Track *_prev;
+
     char *_name;
 
     static queue <Track_Widget *> _delete_queue;
+    static Track_Widget *pushed;
 
 protected:
 
     list <Track_Widget *> _widgets;
     Track_Widget *event_widget ( void );
 
-    const char *class_name ( void ) { return "Track"; }
+    virtual const char *class_name ( void ) { return "Track"; }
 
 
     void set ( char ** ) { return; }
@@ -83,7 +83,6 @@ public:
 
     Track ( int X, int Y, int W, int H ) : Fl_Group( X, Y, W, H )
         {
-            _next = _prev = NULL;
             _name = NULL;
 
             box( FL_DOWN_BOX );
@@ -102,11 +101,6 @@ public:
             log_destroy();
         }
 
-    Track *next ( void ) const { return _next; }
-    Track *prev ( void ) const { return _prev; }
-    void prev ( Track *t ) { _prev = t; }
-    void next ( Track *t ) { _next = t; }
-
     const char * name ( void ) const { return _name; }
     void name ( char *s ) { if ( _name ) free( _name ); _name = s; }
 

Track_Widget.C

@@ -169,6 +169,7 @@ Track_Widget::handle ( int m )
 
             return 1;
         case FL_DRAG:
+        case FL_DND_DRAG:
         {
             if ( ! _drag )
             {