How can add a new codec module to VLC?

[systest]

I'm already add:

vlc_module_begin();
set_description( _("Sigma decoder (using sigma library)") );
set_capability( "decoder", 120 );
set_callbacks( OpenDecoder, CloseDecoder );
add_shortcut( "sigma" );
vlc_module_end();

Anything else need to do? How can I compile this module?

[systest]

Hi, I add some info to configure.ac:
dnl
dnl Switch to enable sigma codec
dnl
AC_ARG_ENABLE(sigma,
[ --enable-sigma Sigma module (default disabled)])
if test "${enable_sigma}" != "no"
then
AC_CHECK_HEADERS(rmexternalapi.h,
[ AX_ADD_BUILTINS([sigma])
AX_ADD_LDFLAGS([sigma],[-lrmcaribbeanapi])
], [ AC_MSG_ERROR([cannot find Simga headers]) ])
fi

And also add "SOURCES_sigma = sigma.c" to modules/codec/Module.am.(sigma.c also in modules/codec/)
Then run ./configure --enable-sigma (with many other options), but nothing happened. The "Makefile" in modules/codec/ didn’t include anything about sigma module.

What's wrong, I'm confused.

[The DJ]

bootstrap first.