typedef struct _GisCallback GisCallback;
typedef struct _GisCallbackClass GisCallbackClass;
+/**
+ * GisCallbackFunc:
+ * @callback: the callback object to be drawn
+ * @user_data: the user data associated with the callback
+ *
+ * A function to be called when the callback object is being rendered
+ */
typedef void (*GisCallbackFunc)(GisCallback *callback, gpointer user_data);
struct _GisCallback {