boilerplate

When I read a blog about boilerplate in Qt, I tried to remember how to write boilerplate code with Gobject. The following code is a frame that I took from 1 year ago I wrote. It is not really hard to understand or write, just need to copy & paste, or use simple tool to auto generate the code. It always need to write more lines in C (GObject) than using C++ for OO. But I don't feel the goodness. I am not feel that is the benifit of C, so I am not sure OO is really good for a Unix developer, so if I can avoid I would avoid the idea of OO in unix platform. (Linux Kernel is not written in OO)

/* macros*/
G_BEGIN_DECLS

#define GST_TYPE_MIDISRC  (gst_my_midisrc_get_type())
#define GST_MIDISRC(obj) (G_TYPE_CHECK_INSTANCE_CAST((obj),GST_TYPE_MIDISRC,GstMidisrc))
#define GST_MIDISRC_CLASS(klass) (G_TYPE_CHECK_CLASS_CAST((klass),GST_TYPE_MIDISRC,GstMidisrcClass))
#define GST_IS_MIDISRC(obj) (G_TYPE_CHECK_INSTANCE_TYPE((obj),GST_TYPE_MIDISRC))
#define GST_IS_MIDISRC_CLASS(obj) (G_TYPE_CHECK_CLASS_TYPE((klass),GST_TYPE_MIDISRC))

/* standard function returning type information */
GType gst_my_midisrc_get_type (void);


/* definition a class of this element */
typedef struct _GstMidisrc GstMidisrc;
struct _GstMidisrc
{
 GstBaseSrc       parent; 
        [...]
};

typedef struct _GstMidisrcClass GstMidisrcClass;

struct _GstMidisrcClass 
{
 GstBaseSrcClass parent_class;
};

G_END_DECLS

Now we can make the boilerplate:

GST_BOILERPLATE (GstMidisrc, gst_my_midisrc, GstBaseSrc, GST_TYPE_BASE_SRC);

After that is the element details.

static GstElementDetails midisrc_details = {
 "A Gstreamer Plug-in", 
 "Src/Audio", 
        "audio src for GStreamer Plug-in", 
        ""
 };

/* set detail with _base_init function when register the plugin */
static void 
gst_my_midisrc_base_init (gpointer klass)
{
 GstElementClass *element_class = GST_ELEMENT_CLASS (klass);
 
 gst_element_class_add_pad_template (element_class, gst_static_pad_template_get (&src_factory));

 gst_element_class_set_details (element_class, &midisrc_details);

}

Then implementation:

/* create the class, here we define which function need to be re-implmented from the base class, and add property for the class */
static void 
gst_my_midisrc_class_init (GstMidisrcClass *klass)
{
 
 GObjectClass *gobject_class;
 GstBaseSrcClass *basesrc_class;
 gobject_class = G_OBJECT_CLASS (klass);
 basesrc_class = GST_BASE_SRC_CLASS (klass);
 gobject_class->set_property = gst_midisrc_set_property;
 gobject_class->get_property = gst_midisrc_get_property;


 /* basesrc_class->get_caps = gst_midisrc_get_caps; 
        basesrc_class->set_caps = gst_midisrc_set_caps; */
        basesrc_class->start = gst_midisrc_start;
        basesrc_class->stop = gst_midisrc_stop; 
        basesrc_class->create = gst_midisrc_create;

        /* install a property for the class as an example */
        g_object_class_install_property (
        gobject_class, ARG_LOCATION,
        g_param_spec_string ("location", "File Location",
             "Location of the file to read", NULL, G_PARAM_READWRITE));



}

/* create the object */
static void 
gst_my_midisrc_init (GstMidisrc *midisrc, GstMidisrcClass *klass)
{ 
   [...]
}

Now the reset part:

/* set property sample */
static gboolean
gst_midisrc_set_location (GstMidisrc * src, const gchar * location)
{
  /* the element must be stopped in order to do this */
  GST_STATE_LOCK (src);
  {
    GstState state;

    state = GST_STATE (src);
    if (state != GST_STATE_READY && state != GST_STATE_NULL)
      goto wrong_state;
  }
  GST_STATE_UNLOCK (src);

  g_free (src->filename);
  g_free (src->uri);

  /* clear the filename if we get a NULL (is that possible?) */
  if (location == NULL) {
    src->filename = NULL;
    src->uri = NULL;
  } else {
    src->filename = g_strdup (location);   
  }
  return TRUE;

  /* ERROR */
wrong_state:
  {
    GST_DEBUG_OBJECT (src, "setting location in wrong state");
    GST_STATE_UNLOCK (src);
    return FALSE;
  }
}
static void
gst_midisrc_set_property (GObject * object,
    guint prop_id, const GValue * value, GParamSpec * pspec)
{
 GstMidisrc *midisrc;
 int tmp = 0;
 g_return_if_fail (GST_IS_MIDISRC (object));
 midisrc = GST_MIDISRC (object);

  switch (prop_id) {
    case ARG_LOCATION:
        gst_midisrc_set_location(midisrc,  g_value_get_string (value));
        printf("set location done!\n");
        break;
    default:
        G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
        break;
   }
}

static void
gst_midisrc_get_property (GObject * object,
    guint prop_id, GValue * value, GParamSpec * pspec)
{
   GstMidisrc *midisrc;

   g_return_if_fail (GST_IS_MIDISRC (object));
   midisrc = GST_MIDISRC (object);

   switch (prop_id) {
    case ARG_LOCATION:
        g_value_set_string(value, midisrc->filename);
        break;
    default:
        G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
        break;
   }
}

static gboolean
gst_midisrc_start (GstBaseSrc * src)
{
   GstMidisrc *midisrc = GST_MIDISRC (src);
        [...]
}

static GstFlowReturn
gst_midisrc_create (GstBaseSrc * src, 
                    guint64 offset,
                    guint length, 
                    GstBuffer ** buffer)
{
    GstMidisrc *midisrc = GST_MIDISRC (src);
    if (midisrc->eos_reached) 
        return GST_FLOW_UNEXPECTED;
    return( gst_midisrc_get_read (src, buffer));
}

static GstFlowReturn
gst_midisrc_get_read (GstBaseSrc * basesrc, GstBuffer ** buffer)
{    
    GstFlowReturn res;
   GstMidisrc *midisrc = GST_MIDISRC (basesrc);
    [...]

    [...]
}

I would like to put my time on learning Git (I was heard git is written by a Unix kernal developer), for desktops, such as gnome or KDE I don't have a lot of interests, I may feel KDE is better since it is written in C++, but who knows.