src/skeleff.c

   1 /* libSoX effect: Skeleton effect used as sample for creating new effects.
   2  *
   3  * Copyright 1999-2008 Chris Bagwell And SoX Contributors
   4  *
   5  * This library is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU Lesser General Public License as published by
   7  * the Free Software Foundation; either version 2.1 of the License, or (at
   8  * your option) any later version.
   9  *
  10  * This library is distributed in the hope that it will be useful, but
  11  * WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser
  13  * General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU Lesser General Public License
  16  * along with this library; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  18  */
  19
  20 #include "sox_i.h"
  21
  22 /* Private data for effect */
  23 typedef struct {
  24   int  localdata;
  25 } priv_t;
  26
  27 /*
  28  * Process command-line options but don't do other
  29  * initialization now: effp->in_signal & effp->out_signal are not
  30  * yet filled in.
  31  */
  32 static int getopts(sox_effect_t * effp, int argc, char UNUSED **argv)
  33 {
  34   priv_t * UNUSED p = (priv_t *)effp->priv;
  35
  36   if (argc != 2)
  37     return lsx_usage(effp);
  38
  39   p->localdata = atoi(argv[1]);
  40
  41   return p->localdata > 0 ? SOX_SUCCESS : SOX_EOF;
  42 }
  43
  44 /*
  45  * Prepare processing.
  46  * Do all initializations.
  47  */
  48 static int start(sox_effect_t * effp)
  49 {
  50   if (effp->out_signal.channels == 1) {
  51     lsx_fail("Can't run on mono data.");
  52     return SOX_EOF;
  53   }
  54
  55   return SOX_SUCCESS;
  56 }
  57
  58 /*
  59  * Process up to *isamp samples from ibuf and produce up to *osamp samples
  60  * in obuf.  Write back the actual numbers of samples to *isamp and *osamp.
  61  * Return SOX_SUCCESS or, if error occurs, SOX_EOF.
  62  */
  63 static int flow(sox_effect_t * effp, const sox_sample_t *ibuf, sox_sample_t *obuf,
  64                            size_t *isamp, size_t *osamp)
  65 {
  66   priv_t * UNUSED p = (priv_t *)effp->priv;
  67   size_t len, done;
  68
  69   switch (effp->out_signal.channels) {
  70   case 2:
  71     /* Length to process will be buffer length / 2 since we
  72      * work with two samples at a time.
  73      */
  74     len = min(*isamp, *osamp) / 2;
  75     for (done = 0; done < len; done++)
  76       {
  77         obuf[0] = ibuf[0];
  78         obuf[1] = ibuf[1];
  79         /* Advance buffer by 2 samples */
  80         ibuf += 2;
  81         obuf += 2;
  82       }
  83
  84     *isamp = len * 2;
  85     *osamp = len * 2;
  86
  87     break;
  88   }
  89
  90   return SOX_SUCCESS;
  91 }
  92
  93 /*
  94  * Drain out remaining samples if the effect generates any.
  95  */
  96 static int drain(sox_effect_t UNUSED * effp, sox_sample_t UNUSED *obuf, size_t *osamp)
  97 {
  98   *osamp = 0;
  99   /* Return SOX_EOF when drain
 100    * will not output any more samples.
 101    * *osamp == 0 also indicates that.
 102    */
 103   return SOX_EOF;
 104 }
 105
 106 /*
 107  * Do anything required when you stop reading samples.
 108  */
 109 static int stop(sox_effect_t UNUSED * effp)
 110 {
 111   return SOX_SUCCESS;
 112 }
 113
 114 /*
 115  * Do anything required when you kill an effect.
 116  *      (free allocated memory, etc.)
 117  */
 118 static int lsx_kill(sox_effect_t UNUSED * effp)
 119 {
 120   return SOX_SUCCESS;
 121 }
 122
 123 /*
 124  * Function returning effect descriptor. This should be the only
 125  * externally visible object.
 126  */
 127 const sox_effect_handler_t *lsx_skel_effect_fn(void);
 128 const sox_effect_handler_t *lsx_skel_effect_fn(void)
 129 {
 130   /*
 131    * Effect descriptor.
 132    * If no specific processing is needed for any of
 133    * the 6 functions, then the function above can be deleted
 134    * and NULL used in place of the its name below.
 135    */
 136   static sox_effect_handler_t sox_skel_effect = {
 137     "skel", "[OPTION]", SOX_EFF_MCHAN,
 138     getopts, start, flow, drain, stop, lsx_kill, sizeof(priv_t)
 139   };
 140   return &sox_skel_effect;
 141 }