gtk-demo: Add a scale example

demos/gtk-demo/scale.c

@@ -0,0 +1,38 @@
+/* Scale
+ *
+ * GtkScale is a way to select a value from a range.
+ * Scales can have marks to help pick special values,
+ * and they can also restrict the values that can be
+ * chosen.
+ */
+
+#include <gtk/gtk.h>
+
+GtkWidget *
+do_scale (GtkWidget *do_widget)
+{
+  static GtkWidget *window = NULL;
+
+  if (!window)
+    {
+      GtkBuilder *builder;
+
+      builder = gtk_builder_new_from_resource ("/scale/scale.ui");
+      gtk_builder_connect_signals (builder, NULL);
+      window = GTK_WIDGET (gtk_builder_get_object (builder, "window1"));
+      gtk_window_set_screen (GTK_WINDOW (window),
+                             gtk_widget_get_screen (do_widget));
+      g_signal_connect (window, "destroy",
+                        G_CALLBACK (gtk_widget_destroyed), &window);
+
+      g_object_unref (builder);
+    }
+
+  if (!gtk_widget_get_visible (window))
+    gtk_widget_show_all (window);
+  else
+    gtk_widget_destroy (window);
+
+
+  return window;
+}