/*
 *  call-seq:
 *    fade_out( fade_time )  ->  self
 *
 *  Fade out to silence over the given number of seconds. Once the sound
 *  is silent, it is automatically stopped.
 *
 *  Returns::     The receiver (self).
 *
 *  **NOTE**: If the sound is currently paused, the fade will start,
 *  but you won't be able to hear it happening unless you #unpause during
 *  the fade. Does nothing if the sound is currently stopped.
 *
 */
static VALUE rg_sound_fadeout( VALUE self, VALUE fade_time )
{
        RG_Sound *sound;
        Data_Get_Struct(self,  RG_Sound, sound);

        int channel = sound->channel;
        int fade_ms = (int)(1000 * NUM2DBL(fade_time));

        /* Make sure the sound actually belongs to the channel */
        if( _rg_sound_channel_check(sound) )
        {
                Mix_FadeOutChannel( channel, fade_ms );
        }

        return self;
}