Add a cleaned-up example for listbox DND

I want to refer to this as an example, so make it look nice.

examples/Makefile.am

@@ -28,7 +28,8 @@ noinst_PROGRAMS = \
 	grid-packing				\
 	drawing					\
 	builder					\
-	search-bar
+	search-bar				\
+	listbox-dnd
 
 EXTRA_DIST = builder.ui
 

examples/listbox-dnd.c

@@ -0,0 +1,155 @@
+#include <gtk/gtk.h>
+
+static GtkTargetEntry entries[] = {
+  { "GTK_LIST_BOX_ROW", GTK_TARGET_SAME_APP, 0 }
+};
+
+static void
+drag_begin (GtkWidget      *widget,
+            GdkDragContext *context,
+            gpointer        data)
+{
+  GtkWidget *row;
+  GtkAllocation alloc;
+  cairo_surface_t *surface;
+  cairo_t *cr;
+  int x, y;
+
+  row = gtk_widget_get_ancestor (widget, GTK_TYPE_LIST_BOX_ROW);
+  gtk_widget_get_allocation (row, &alloc);
+  surface = cairo_image_surface_create (CAIRO_FORMAT_ARGB32, alloc.width, alloc.height);
+  cr = cairo_create (surface);
+
+  gtk_style_context_add_class (gtk_widget_get_style_context (row), "drag-icon");
+  gtk_widget_draw (row, cr);
+  gtk_style_context_remove_class (gtk_widget_get_style_context (row), "drag-icon");
+
+  gtk_widget_translate_coordinates (widget, row, 0, 0, &x, &y);
+  cairo_surface_set_device_offset (surface, -x, -y);
+  gtk_drag_set_icon_surface (context, surface);
+
+  cairo_destroy (cr);
+  cairo_surface_destroy (surface);
+}
+
+void
+drag_data_get (GtkWidget        *widget,
+               GdkDragContext   *context,
+               GtkSelectionData *selection_data,
+               guint             info,
+               guint             time,
+               gpointer          data)
+{
+  gtk_selection_data_set (selection_data,
+                          gdk_atom_intern_static_string ("GTK_LIST_BOX_ROW"),
+                          32,
+                          (const guchar *)&widget,
+                          sizeof (gpointer));
+}
+
+static void
+drag_data_received (GtkWidget        *widget,
+                    GdkDragContext   *context,
+                    gint              x,
+                    gint              y,
+                    GtkSelectionData *selection_data,
+                    guint             info,
+                    guint32           time,
+                    gpointer          data)
+{
+  GtkWidget *target;
+  GtkWidget *row;
+  GtkWidget *source;
+  int pos;
+
+  target = widget;
+
+  pos = gtk_list_box_row_get_index (GTK_LIST_BOX_ROW (target));
+  row = (gpointer)* (gpointer*)gtk_selection_data_get_data (selection_data);
+  source = gtk_widget_get_ancestor (row, GTK_TYPE_LIST_BOX_ROW);
+
+  if (source == target)
+    return;
+
+  g_object_ref (source);
+  gtk_container_remove (GTK_CONTAINER (gtk_widget_get_parent (source)), source);
+  gtk_list_box_insert (GTK_LIST_BOX (gtk_widget_get_parent (target)), source, pos);
+  g_object_unref (source);
+}
+
+static GtkWidget *
+create_row (const gchar *text)
+{
+  GtkWidget *row, *handle, *box, *label, *image;
+
+  row = gtk_list_box_row_new ();
+
+  box = gtk_box_new (GTK_ORIENTATION_HORIZONTAL, 10);
+  g_object_set (box, "margin-start", 10, "margin-end", 10, NULL);
+  gtk_container_add (GTK_CONTAINER (row), box);
+
+  handle = gtk_event_box_new ();
+  image = gtk_image_new_from_icon_name ("open-menu-symbolic", 1);
+  gtk_container_add (GTK_CONTAINER (handle), image);
+  gtk_container_add (GTK_CONTAINER (box), handle);
+
+  label = gtk_label_new (text);
+  gtk_container_add_with_properties (GTK_CONTAINER (box), label, "expand", TRUE, NULL);
+
+  gtk_drag_source_set (handle, GDK_BUTTON1_MASK, entries, 1, GDK_ACTION_MOVE);
+  g_signal_connect (handle, "drag-begin", G_CALLBACK (drag_begin), NULL);
+  g_signal_connect (handle, "drag-data-get", G_CALLBACK (drag_data_get), NULL);
+
+  gtk_drag_dest_set (row, GTK_DEST_DEFAULT_ALL, entries, 1, GDK_ACTION_MOVE);
+  g_signal_connect (row, "drag-data-received", G_CALLBACK (drag_data_received), NULL);
+
+  return row;
+}
+
+static const char *css =
+  ".drag-icon { "
+  "  background: white; "
+  "  border: 1px solid black; "
+  "}";
+
+int
+main (int argc, char *argv[])
+{
+  GtkWidget *window, *list, *sw, *row;
+  gint i;
+  gchar *text;
+  GtkCssProvider *provider;
+
+  gtk_init (NULL, NULL);
+
+  provider = gtk_css_provider_new ();
+  gtk_css_provider_load_from_data (provider, css, -1, NULL);
+  gtk_style_context_add_provider_for_screen (gdk_screen_get_default (),
+                                             GTK_STYLE_PROVIDER (provider),
+                                             GTK_STYLE_PROVIDER_PRIORITY_APPLICATION);
+
+  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
+  gtk_window_set_default_size (GTK_WINDOW (window), -1, 300);
+
+  sw = gtk_scrolled_window_new (NULL, NULL);
+  gtk_widget_set_hexpand (sw, TRUE);
+  gtk_scrolled_window_set_policy (GTK_SCROLLED_WINDOW (sw), GTK_POLICY_NEVER, GTK_POLICY_ALWAYS);
+  gtk_container_add (GTK_CONTAINER (window), sw);
+
+  list = gtk_list_box_new ();
+  gtk_list_box_set_selection_mode (GTK_LIST_BOX (list), GTK_SELECTION_NONE);
+  gtk_container_add (GTK_CONTAINER (sw), list);
+
+  for (i = 0; i < 20; i++)
+    {
+      text = g_strdup_printf ("Row %d", i);
+      row = create_row (text);
+      gtk_list_box_insert (GTK_LIST_BOX (list), row, -1);
+    }
+
+  gtk_widget_show_all (window);
+
+  gtk_main ();
+
+  return 0;
+}