View source for Hacker Guide/How To Write a Module

* This guide is being written by a {{VLC}} novice.  Please check all statements below.
* Using [http://trac.videolan.org/vlc/browser/trunk/modules/access/dvdread.c dvdread.c] as the template.


== Module Descriptor ==

A {{VLC}} Module must include a description of itself, and the parameters it accepts.

The module descriptor begins with:
<pre>
vlc_module_begin();
</pre>

You should set some category information on your module:
<pre>
    set_shortname( _("DVD without menus") );
    set_description( _("DVDRead Input (DVD without menu support)") );
    set_category( CAT_INPUT );
</pre>
Note the use of _("") to create a string that needs to be translated.

Predefined Categories include:
* CAT_INTERFACE 
* CAT_AUDIO
* CAT_VIDEO
* CAT_INPUT
* CAT_SOUT
* CAT_ADVANCED
* CAT_PLAYLIST

<pre>
    set_subcategory( SUBCAT_INPUT_ACCESS );
</pre>
See [http://trac.videolan.org/vlc/browser/trunk/include/vlc_configuration.h include/vlc_configuration.h] 
for definition of all categories and sub-categories.

=== Adding Parameters ===
All macros take the following argument list:
<pre> add_integer(name, value, p_callback, text, longtext, advc) </pre>
* '''name''' is the string that identifies this parameter in the configuration.  This name may be used at the command prompt to set the configuration value.
* '''value''' is the default value for this parameter,
* '''p_callback''' is a function pointer that will be called when the value of this parameter is changed.
** p_callback is called with the following arguments:  <pre>( p_this, psz_name, oldval, val, p_config->p_callback_data )</pre>
*** '''p_this''' is a pointer to a vlc_object_t struct,
*** '''psz_name''' is the '''name''' of your parameter that is being changed,
*** '''oldval''' is the old value of the parameter,
*** '''val''' is the new value of the parameter,
*** '''p_call_back_data''' is void* data that you can assign for each parameter.  Usually NULL.
* '''text''' A short description of the parameter,
* '''longtext''' A complete description of the parameter,
* '''advc''' Boolean, ADVanced Configuration.  If TRUE, this parameter will only be displayed when using the --advanced flag. e.g. 
<pre>vlc -p dvdread --advanced</pre>

e.g.
<pre> add_integer("dvdread-angle", 1, NULL, "DVD Angle", "Default DVD Angle", NULL") </pre>

You may add the following parameters to your module:
* add_integer,
* add_string,
* add_float,
* add_bool,
* add_key,
* add_file,
* add_directory,

For complete definitions, see [http://trac.videolan.org/vlc/browser/trunk/include/vlc_configuration.h include/vlc_configuration.h]

== Open(vlc_object_t *) ==

== Close(vlc_object_t *) ==

[[Category:Coding]]