mix.c

SDL_mixer 是一个基于 SDL 的混音器

		}
	  }
	return;
      }
}

static void mix_single_right_signal(resample_t *sp, int32 *lp, int v, int count)
{
  Voice *vp = voice + v;
  final_volume_t 
    left=vp->left_mix;
  int cc;
  resample_t s;
  
  if (!(cc = vp->control_counter))
    {
      cc = control_ratio;
      if (update_signal(v))
	return;	/* Envelope ran out */
      left = vp->left_mix;
    }
  
  while (count)
    if (cc < count)
      {
	count -= cc;
	while (cc--)
	  {
	    s = *sp++;
		if (num_ochannels == 2) {
	    		MIXSKIP;
			MIXATION(left);
		}
		if (num_ochannels >= 4) {
	    		MIXSKIP;
			MIXHALF(left);
	    		MIXSKIP;
			MIXATION(left);
		} if (num_ochannels == 6) {
	    		MIXSKIP;
			MIXATION(left);
		}
	  }
	cc = control_ratio;
	if (update_signal(v))
	  return;	/* Envelope ran out */
	left = vp->left_mix;
      }
    else
      {
	vp->control_counter = cc - count;
	while (count--)
	  {
	    s = *sp++;
		if (num_ochannels == 2) {
	    		MIXSKIP;
			MIXATION(left);
		}
		if (num_ochannels >= 4) {
	    		MIXSKIP;
			MIXHALF(left);
	    		MIXSKIP;
			MIXATION(left);
		} if (num_ochannels == 6) {
	    		MIXSKIP;
			MIXATION(left);
		}
	  }
	return;
      }
}

static void mix_mono_signal(resample_t *sp, int32 *lp, int v, int count)
{
  Voice *vp = voice + v;
  final_volume_t 
    left=vp->left_mix;
  int cc;
  resample_t s;
  
  if (!(cc = vp->control_counter))
    {
      cc = control_ratio;
      if (update_signal(v))
	return;	/* Envelope ran out */
      left = vp->left_mix;
    }
  
  while (count)
    if (cc < count)
      {
	count -= cc;
	while (cc--)
	  {
	    s = *sp++;
	    MIXATION(left);
	  }
	cc = control_ratio;
	if (update_signal(v))
	  return;	/* Envelope ran out */
	left = vp->left_mix;
      }
    else
      {
	vp->control_counter = cc - count;
	while (count--)
	  {
	    s = *sp++;
	    MIXATION(left);
	  }
	return;
      }
}

static void mix_mystery(resample_t *sp, int32 *lp, int v, int count)
{
  final_volume_t 
    left_rear=voice[v].lr_mix, 
    left=voice[v].left_mix, 
    center=voice[v].ce_mix, 
    right=voice[v].right_mix, 
    right_rear=voice[v].rr_mix, 
    lfe=voice[v].lfe_mix;
  resample_t s;
  
  while (count--)
    {
      s = *sp++;
	      	MIXATION(left);
	      	MIXATION(right);
		if (num_ochannels >= 4) {
			MIXATION(left_rear);
			MIXATION(right_rear);
		}
		if (num_ochannels == 6) {
			MIXATION(center);
			MIXATION(lfe);
		}
    }
}

static void mix_center(resample_t *sp, int32 *lp, int v, int count)
{
  final_volume_t 
    left=voice[v].left_mix;
  resample_t s;
  
  while (count--)
    {
      s = *sp++;
		if (num_ochannels == 2) {
      			MIXATION(left);
      			MIXATION(left);
		}
		else if (num_ochannels == 4) {
      			MIXATION(left);
      			MIXATION(left);
			MIXSKIP;
			MIXSKIP;
		}
		else if (num_ochannels == 6) {
			MIXSKIP;
			MIXSKIP;
			MIXSKIP;
			MIXSKIP;
			MIXATION(left);
			MIXATION(left);
		}
    }
}

static void mix_single_left(resample_t *sp, int32 *lp, int v, int count)
{
  final_volume_t 
    left=voice[v].left_mix;
  resample_t s;
  
  while (count--)
    {
      s = *sp++;
		if (num_ochannels == 2) {
			MIXATION(left);
      			MIXSKIP;
		}
		if (num_ochannels >= 4) {
			MIXHALF(left);
      			MIXSKIP;
			MIXATION(left);
      			MIXSKIP;
		}
	       	if (num_ochannels == 6) {
      			MIXSKIP;
			MIXATION(left);
		}
    }
}
static void mix_single_right(resample_t *sp, int32 *lp, int v, int count)
{
  final_volume_t 
    left=voice[v].left_mix;
  resample_t s;
  
  while (count--)
    {
      s = *sp++;
		if (num_ochannels == 2) {
      			MIXSKIP;
			MIXATION(left);
		}
		if (num_ochannels >= 4) {
      			MIXSKIP;
			MIXHALF(left);
      			MIXSKIP;
			MIXATION(left);
		}
	       	if (num_ochannels == 6) {
      			MIXSKIP;
			MIXATION(left);
		}
    }
}

static void mix_mono(resample_t *sp, int32 *lp, int v, int count)
{
  final_volume_t 
    left=voice[v].left_mix;
  resample_t s;
  
  while (count--)
    {
      s = *sp++;
      MIXATION(left);
    }
}

/* Ramp a note out in c samples */
static void ramp_out(resample_t *sp, int32 *lp, int v, int32 c)
{

  /* should be final_volume_t, but uint8 gives trouble. */
  int32 left_rear, left, center, right, right_rear, lfe, li, ri;

  resample_t s = 0; /* silly warning about uninitialized s */

  /* Fix by James Caldwell */
  if ( c == 0 ) c = 1;

  left = voice[v].left_mix;
  li = -(left/c);
  if (!li) li = -1;

  /* printf("Ramping out: left=%d, c=%d, li=%d\n", left, c, li); */

  if (!(play_mode->encoding & PE_MONO))
    {
      if (voice[v].panned==PANNED_MYSTERY)
	{
	  left_rear = voice[v].lr_mix;
	  center=voice[v].ce_mix;
	  right=voice[v].right_mix;
	  right_rear = voice[v].rr_mix;
	  lfe = voice[v].lfe_mix;

	  ri=-(right/c);
	  while (c--)
	    {
	      left_rear += li; if (left_rear<0) left_rear=0;
	      left += li; if (left<0) left=0;
	      center += li; if (center<0) center=0;
	      right += ri; if (right<0) right=0;
	      right_rear += ri; if (right_rear<0) right_rear=0;
	      lfe += li; if (lfe<0) lfe=0;
	      s=*sp++;
	      	MIXATION(left);
	      	MIXATION(right);
		if (num_ochannels >= 4) {
			MIXATION(left_rear);
			MIXATION(right_rear);
		}
		if (num_ochannels == 6) {
			MIXATION(center);
			MIXATION(lfe);
		}
	    }
	}
      else if (voice[v].panned==PANNED_CENTER)
	{
	  while (c--)
	    {
	      left += li;
	      if (left<0)
		return;
	      s=*sp++;	
		if (num_ochannels == 2) {
	      		MIXATION(left);
	      		MIXATION(left);
		}
		else if (num_ochannels == 4) {
			MIXATION(left);
	      		MIXATION(left);
			MIXSKIP;
			MIXSKIP;
		}
		else if (num_ochannels == 6) {
			MIXSKIP;
			MIXSKIP;
			MIXSKIP;
			MIXSKIP;
	      		MIXATION(left);
	      		MIXATION(left);
		}
	    }
	}
      else if (voice[v].panned==PANNED_LEFT)
	{
	  while (c--)
	    {
	      left += li;
	      if (left<0)
		return;
	      s=*sp++;
	      MIXATION(left);
	      MIXSKIP;
		if (num_ochannels >= 4) {
			MIXATION(left);
	      		MIXSKIP;
		} if (num_ochannels == 6) {
			MIXATION(left);
			MIXATION(left);
		}
	    }
	}
      else if (voice[v].panned==PANNED_RIGHT)
	{
	  while (c--)
	    {
	      left += li;
	      if (left<0)
		return;
	      s=*sp++;
	      MIXSKIP;
	      MIXATION(left);
		if (num_ochannels >= 4) {
	      		MIXSKIP;
			MIXATION(left);
		} if (num_ochannels == 6) {
			MIXATION(left);
			MIXATION(left);
		}
	    }
	}
    }
  else
    {
      /* Mono output.  */
      while (c--)
	{
	  left += li;
	  if (left<0)
	    return;
	  s=*sp++;
	  MIXATION(left);
	}
    }
}


/**************** interface function ******************/

void mix_voice(int32 *buf, int v, int32 c)
{
  Voice *vp=voice+v;
  int32 count=c;
  resample_t *sp;
  if (c<0) return;
  if (vp->status==VOICE_DIE)
    {
      if (count>=MAX_DIE_TIME)
	count=MAX_DIE_TIME;
      sp=resample_voice(v, &count);
      ramp_out(sp, buf, v, count);
      vp->status=VOICE_FREE;
    }
  else
    {
      sp=resample_voice(v, &count);
      if (count<0) return;
      if (play_mode->encoding & PE_MONO)
	{
	  /* Mono output. */
	  if (vp->envelope_increment || vp->tremolo_phase_increment)
	    mix_mono_signal(sp, buf, v, count);
	  else
	    mix_mono(sp, buf, v, count);
	}
      else
	{
	  if (vp->panned == PANNED_MYSTERY)
	    {
	      if (vp->envelope_increment || vp->tremolo_phase_increment)
		mix_mystery_signal(sp, buf, v, count);
	      else
		mix_mystery(sp, buf, v, count);
	    }
	  else if (vp->panned == PANNED_CENTER)
	    {
	      if (vp->envelope_increment || vp->tremolo_phase_increment)
		mix_center_signal(sp, buf, v, count);
	      else
		mix_center(sp, buf, v, count);
	    }
	  else
	    { 
	      /* It's either full left or full right. In either case,
		 every other sample is 0. Just get the offset right: */
	      
	      if (vp->envelope_increment || vp->tremolo_phase_increment)
	      {
	        if (vp->panned == PANNED_RIGHT)
			mix_single_right_signal(sp, buf, v, count);
		else mix_single_left_signal(sp, buf, v, count);
	      }
	      else 
	      {
	        if (vp->panned == PANNED_RIGHT)
			mix_single_right(sp, buf, v, count);
		else mix_single_left(sp, buf, v, count);
	      }
	    }
	}
    }
}