Drag n drop, GTK and C

/*
* icon.c - GtkIconView DnD sample (non-working) application
*
* For non-working example compile with:
*   gcc -o icon icon.c $(pkg-config --cflags --libs gtk+-2.0)
*
* else
*   gcc -DNONEMPTY -o icon icon.c $(pkg-config --cflags --libs gtk+-2.0)
*
*/

#include <gtk/gtk.h>

enum
{
   COL_TEXT = 0,
   COL_PICT,
   N_COLS
};

static GtkTreeModel *create_model( gboolean populate );

static GtkWidget *create_icon_view( gboolean populate );

static gboolean cb_drag_drop( GtkWidget      *icon,
                       GdkDragContext *context,
                       gint            x,
                       gint            y,
                       guint           time,
                       gpointer        data );

int
main( int    argc,
     char **argv )
{
   GtkWidget    *window;
   GtkWidget    *hbox;
   GtkWidget    *icon1;
   GtkWidget    *icon2;

   gtk_init( &argc, &argv );

   window = gtk_window_new( GTK_WINDOW_TOPLEVEL );
   gtk_window_set_default_size( GTK_WINDOW( window ), 400, 300 );
   gtk_container_set_border_width( GTK_CONTAINER( window ), 6 );
   g_signal_connect( G_OBJECT( window ), "destroy",
                 G_CALLBACK( gtk_main_quit ), NULL );

   hbox = gtk_hbox_new( TRUE, 6 );
   gtk_container_add( GTK_CONTAINER( window ), hbox );

   icon1 = create_icon_view( TRUE );
   gtk_widget_set_name( icon1, "Left iconview" );
   gtk_box_pack_start( GTK_BOX( hbox ), icon1, TRUE, TRUE, 0 );

   icon2 = create_icon_view( FALSE );
   gtk_widget_set_name( icon2, "Right iconview" );
   gtk_box_pack_start( GTK_BOX( hbox ), icon2, TRUE, TRUE, 0 );

   gtk_widget_show_all( window );

   gtk_main();

   return( 0 );
}

static GtkWidget *
create_icon_view( gboolean populate )
{
   GtkWidget             *icon;
   GtkTreeModel          *model;

   static GtkTargetEntry *target = NULL;

   if( ! target )
   {
      target = g_slice_new(GtkTargetEntry);
      target->target = "InternalTarget";
      target->flags  = GTK_TARGET_SAME_APP;
      target->info   = 0;
   }

   model = create_model( populate );
   icon = gtk_icon_view_new_with_model( model );
   g_object_unref( G_OBJECT( model ) );

   gtk_icon_view_set_text_column( GTK_ICON_VIEW( icon ), COL_TEXT );
   gtk_icon_view_set_pixbuf_column( GTK_ICON_VIEW( icon ), COL_PICT );

   /* DnD setup */
   gtk_icon_view_enable_model_drag_source( GTK_ICON_VIEW( icon ),
                                 GDK_BUTTON1_MASK, target, 1,
                                 GDK_ACTION_MOVE );
   gtk_icon_view_enable_model_drag_dest( GTK_ICON_VIEW( icon ), target, 1,
                                GDK_ACTION_MOVE );

   g_signal_connect( G_OBJECT( icon ), "drag-drop",
                 G_CALLBACK( cb_drag_drop ), NULL );

   return( icon );
}

static GtkTreeModel *
create_model( gboolean populate )
{
   GtkListStore *store;
   GtkTreeIter   iter;
   GdkPixbuf    *pix;

   store = gtk_list_store_new( N_COLS, G_TYPE_STRING, GDK_TYPE_PIXBUF );

   if( ! populate )
   {
      /* This piece of code makes all the difference */
#ifdef NONEMPTY
      pix = gdk_pixbuf_new( GDK_COLORSPACE_RGB, FALSE, 8, 50, 50 );
      gdk_pixbuf_fill( pix, 0xff000000 ); /* Red */
      gtk_list_store_append( store, &iter );
      gtk_list_store_set( store, &iter, COL_TEXT, "R 4", COL_PICT, pix, -1 );
      g_object_unref( G_OBJECT( pix ) );
#endif /* NONEMPTY */
   }
   else
   {
      pix = gdk_pixbuf_new( GDK_COLORSPACE_RGB, FALSE, 8, 50, 50 );
      gdk_pixbuf_fill( pix, 0x00000000 ); /* Black */
      gtk_list_store_append( store, &iter );
      gtk_list_store_set( store, &iter, COL_TEXT, "R 1", COL_PICT, pix, -1 );
      g_object_unref( G_OBJECT( pix ) );

      pix = gdk_pixbuf_new( GDK_COLORSPACE_RGB, FALSE, 8, 50, 50 );
      gdk_pixbuf_fill( pix, 0x0000ff00 ); /* Blue */
      gtk_list_store_append( store, &iter );
      gtk_list_store_set( store, &iter, COL_TEXT, "R 2", COL_PICT, pix, -1 );
      g_object_unref( G_OBJECT( pix ) );

      pix = gdk_pixbuf_new( GDK_COLORSPACE_RGB, FALSE, 8, 50, 50 );
      gdk_pixbuf_fill( pix, 0x00ff0000 ); /* Green */
      gtk_list_store_append( store, &iter );
      gtk_list_store_set( store, &iter, COL_TEXT, "R 3", COL_PICT, pix, -1 );
      g_object_unref( G_OBJECT( pix ) );
   }

   return( GTK_TREE_MODEL( store ) );
}

static gboolean
cb_drag_drop( GtkWidget      *icon,
           GdkDragContext *context,
           gint            x,
           gint            y,
           guint           time,
           gpointer        data )
{
   GdkAtom target_type;

   g_print( "Detected drop on %s\n", gtk_widget_get_name( icon ) );

   target_type = GDK_POINTER_TO_ATOM( context->targets->data );
   gtk_drag_get_data( icon, context, target_type, time );

   return( TRUE );
}