resample.c

SDL_mixer 是一个基于 SDL 的混音器

  INTERPVARS;
  Voice *vp=&voice[v];
  resample_t 
    *dest=resample_buffer; 
  sample_t 
    *src=vp->sample->data;
  int32 
    le=vp->sample->data_length,
    ofs=vp->sample_offset, 
    incr=vp->sample_increment, 
    count=*countptr;
  int 
    cc=vp->vibrato_control_counter;

  /* This has never been tested */

  if (incr<0) incr = -incr; /* In case we're coming out of a bidir loop */

  while (count--)
    {
      if (!cc--)
	{
	  cc=vp->vibrato_control_ratio;
	  incr=update_vibrato(vp, 0);
	}
      RESAMPLATION;
      ofs += incr;
      if (ofs >= le)
	{
	  FINALINTERP;
	  vp->status=VOICE_FREE;
 	  ctl->note(v);
	  *countptr-=count+1;
	  break;
	}
    }
  
  vp->vibrato_control_counter=cc;
  vp->sample_increment=incr;
  vp->sample_offset=ofs; /* Update offset */
  return resample_buffer;
}

static resample_t *rs_vib_loop(Voice *vp, int32 count)
{

  /* Play sample until end-of-loop, skip back and continue. */
  
  INTERPVARS;
  int32 
    ofs=vp->sample_offset, 
    incr=vp->sample_increment, 
    le=vp->sample->loop_end,
    ll=le - vp->sample->loop_start;
  resample_t 
    *dest=resample_buffer; 
  sample_t 
    *src=vp->sample->data;
  int 
    cc=vp->vibrato_control_counter;

#ifdef PRECALC_LOOPS
  int32 i;
  int
    vibflag=0;

  while (count) 
    {
      /* Hopefully the loop is longer than an increment */
      if(ofs >= le)
	ofs -= ll;
      /* Precalc how many times to go through the loop, taking
	 the vibrato control ratio into account this time. */
      i = (le - ofs) / incr + 1;
      if(i > count) i = count;
      if(i > cc)
	{
	  i = cc;
	  vibflag = 1;
	} 
      else cc -= i;
      count -= i;
      while(i--) 
	{
	  RESAMPLATION;
	  ofs += incr;
	}
      if(vibflag) 
	{
	  cc = vp->vibrato_control_ratio;
	  incr = update_vibrato(vp, 0);
	  vibflag = 0;
	}
    }

#else /* PRECALC_LOOPS */
  while (count--)
    {
      if (!cc--)
	{
	  cc=vp->vibrato_control_ratio;
	  incr=update_vibrato(vp, 0);
	}
      RESAMPLATION;
      ofs += incr;
      if (ofs>=le)
	ofs -= ll; /* Hopefully the loop is longer than an increment. */
    }
#endif /* PRECALC_LOOPS */

  vp->vibrato_control_counter=cc;
  vp->sample_increment=incr;
  vp->sample_offset=ofs; /* Update offset */
  return resample_buffer;
}

static resample_t *rs_vib_bidir(Voice *vp, int32 count)
{
  INTERPVARS;
  int32 
    ofs=vp->sample_offset, 
    incr=vp->sample_increment,
    le=vp->sample->loop_end, 
    ls=vp->sample->loop_start;
  resample_t 
    *dest=resample_buffer; 
  sample_t 
    *src=vp->sample->data;
  int 
    cc=vp->vibrato_control_counter;

#ifdef PRECALC_LOOPS
  int32
    le2=le<<1,
    ls2=ls<<1,
    i;
  int
    vibflag = 0;

  /* Play normally until inside the loop region */
  while (count && (ofs <= ls)) 
    {
      i = (ls - ofs) / incr + 1;
      if (i > count) i = count;
      if (i > cc) 
	{
	  i = cc;
	  vibflag = 1;
	} 
      else cc -= i;
      count -= i;
      while (i--) 
	{
	  RESAMPLATION;
	  ofs += incr;
	}
      if (vibflag) 
	{
	  cc = vp->vibrato_control_ratio;
	  incr = update_vibrato(vp, 0);
	  vibflag = 0;
	}
    }
  
  /* Then do the bidirectional looping */

  while (count) 
    {
      /* Precalc how many times we should go through the loop */
      i = ((incr > 0 ? le : ls) - ofs) / incr + 1;
      if(i > count) i = count;
      if(i > cc) 
	{
	  i = cc;
	  vibflag = 1;
	} 
      else cc -= i;
      count -= i;
      while (i--) 
	{
	  RESAMPLATION;
	  ofs += incr;
	}
      if (vibflag) 
	{
	  cc = vp->vibrato_control_ratio;
	  incr = update_vibrato(vp, (incr < 0));
	  vibflag = 0;
	}
      if (ofs >= le) 
	{
	  /* fold the overshoot back in */
	  ofs = le2 - ofs;
	  incr *= -1;
	} 
      else if (ofs <= ls) 
	{
	  ofs = ls2 - ofs;
	  incr *= -1;
	}
    }

#else /* PRECALC_LOOPS */
  /* Play normally until inside the loop region */

  if (ofs < ls)
    {
      while (count--)
	{
	  if (!cc--)
	    {
	      cc=vp->vibrato_control_ratio;
	      incr=update_vibrato(vp, 0);
	    }
	  RESAMPLATION;
	  ofs += incr;
	  if (ofs>=ls)
	    break;
	}
    }

  /* Then do the bidirectional looping */

  if (count>0)
    while (count--)
      {
	if (!cc--)
	  {
	    cc=vp->vibrato_control_ratio;
	    incr=update_vibrato(vp, (incr < 0));
	  }
	RESAMPLATION;
	ofs += incr;
	if (ofs>=le)
	  {
	    /* fold the overshoot back in */
	    ofs = le - (ofs - le);
	    incr = -incr;
	  }
	else if (ofs <= ls)
	  {
	    ofs = ls + (ls - ofs);
	    incr = -incr;
	  }
      }
#endif /* PRECALC_LOOPS */

  vp->vibrato_control_counter=cc;
  vp->sample_increment=incr;
  vp->sample_offset=ofs; /* Update offset */
  return resample_buffer;
}

resample_t *resample_voice(int v, int32 *countptr)
{
  int32 ofs;
  uint8 modes;
  Voice *vp=&voice[v];
  
  if (!(vp->sample->sample_rate))
    {
      /* Pre-resampled data -- just update the offset and check if
         we're out of data. */
      ofs=vp->sample_offset >> FRACTION_BITS; /* Kind of silly to use
						 FRACTION_BITS here... */
      if (*countptr >= (vp->sample->data_length>>FRACTION_BITS) - ofs)
	{
	  /* Note finished. Free the voice. */
	  vp->status = VOICE_FREE;
	  ctl->note(v);
	  
	  /* Let the caller know how much data we had left */
	  *countptr = (vp->sample->data_length>>FRACTION_BITS) - ofs;
	}
      else
	vp->sample_offset += *countptr << FRACTION_BITS;
      
      return (resample_t *)vp->sample->data+ofs;
    }

  /* Need to resample. Use the proper function. */
  modes=vp->sample->modes;

  if (vp->vibrato_control_ratio)
    {
      if ((modes & MODES_LOOPING) &&
	  ((modes & MODES_ENVELOPE) ||
	   (vp->status==VOICE_ON || vp->status==VOICE_SUSTAINED)))
	{
	  if (modes & MODES_PINGPONG)
	    return rs_vib_bidir(vp, *countptr);
	  else
	    return rs_vib_loop(vp, *countptr);
	}
      else
	return rs_vib_plain(v, countptr);
    }
  else
    {
      if ((modes & MODES_LOOPING) &&
	  ((modes & MODES_ENVELOPE) ||
	   (vp->status==VOICE_ON || vp->status==VOICE_SUSTAINED)))
	{
	  if (modes & MODES_PINGPONG)
	    return rs_bidir(vp, *countptr);
	  else
	    return rs_loop(vp, *countptr);
	}
      else
	return rs_plain(v, countptr);
    }
}

void pre_resample(Sample * sp)
{
  double a, xdiff;
  int32 incr, ofs, newlen, count;
  int16 *src = (int16 *) sp->data;
  resample_t *newdata, *dest;
  int16 v1, v2, v3, v4, *vptr;
  static const char note_name[12][3] =
  {
    "C", "C#", "D", "D#", "E", "F", "F#", "G", "G#", "A", "A#", "B"
  };

  ctl->cmsg(CMSG_INFO, VERB_NOISY, " * pre-resampling for note %d (%s%d)",
	    sp->note_to_use,
	    note_name[sp->note_to_use % 12], (sp->note_to_use & 0x7F) / 12);

  a = ((double) (sp->sample_rate) * freq_table[(int) (sp->note_to_use)]) /
    ((double) (sp->root_freq) * play_mode->rate);
  if (a <= 0) return;
  newlen = (int32)(sp->data_length / a);
  if (newlen < 0 || (newlen >> FRACTION_BITS) > MAX_SAMPLE_SIZE) return;
  dest = newdata = safe_malloc(newlen >> (FRACTION_BITS - 1));

  count = (newlen >> FRACTION_BITS) - 1;
  ofs = incr = (sp->data_length - (1 << FRACTION_BITS)) / count;

  if (--count)
    *dest++ = src[0];

  /* Since we're pre-processing and this doesn't have to be done in
     real-time, we go ahead and do the full sliding cubic interpolation. */
  while (--count)
    {
      vptr = src + (ofs >> FRACTION_BITS);
      v1 = *(vptr - 1);
      v2 = *vptr;
      v3 = *(vptr + 1);
      v4 = *(vptr + 2);
      xdiff = FSCALENEG(ofs & FRACTION_MASK, FRACTION_BITS);
      *dest++ = (int16)(v2 + (xdiff / 6.0) * (-2 * v1 - 3 * v2 + 6 * v3 - v4 +
      xdiff * (3 * (v1 - 2 * v2 + v3) + xdiff * (-v1 + 3 * (v2 - v3) + v4))));
      ofs += incr;
    }

  if (ofs & FRACTION_MASK)
    {
      v1 = src[ofs >> FRACTION_BITS];
      v2 = src[(ofs >> FRACTION_BITS) + 1];
      *dest++ = (resample_t)(v1 + (((v2 - v1) * (ofs & FRACTION_MASK)) >> FRACTION_BITS));
    }
  else
    *dest++ = src[ofs >> FRACTION_BITS];

  sp->data_length = newlen;
  sp->loop_start = (int32)(sp->loop_start / a);
  sp->loop_end = (int32)(sp->loop_end / a);
  free(sp->data);
  sp->data = (sample_t *) newdata;
  sp->sample_rate = 0;
}