OpenAL32/Include/alFilter.h

   1 #ifndef _AL_FILTER_H_
   2 #define _AL_FILTER_H_
   3
   4 #include "AL/al.h"
   5 #include "alu.h"
   6
   7 #ifdef __cplusplus
   8 extern "C" {
   9 #endif
  10
  11 typedef struct {
  12     ALfloat coeff;
  13 #ifndef _MSC_VER
  14     ALfloat history[0];
  15 #else
  16     ALfloat history[1];
  17 #endif
  18 } FILTER;
  19
  20 static __inline ALfloat lpFilter4P(FILTER *iir, ALuint offset, ALfloat input)
  21 {
  22     ALfloat *history = &iir->history[offset];
  23     ALfloat a = iir->coeff;
  24     ALfloat output = input;
  25
  26     output = output + (history[0]-output)*a;
  27     history[0] = output;
  28     output = output + (history[1]-output)*a;
  29     history[1] = output;
  30     output = output + (history[2]-output)*a;
  31     history[2] = output;
  32     output = output + (history[3]-output)*a;
  33     history[3] = output;
  34
  35     return output;
  36 }
  37
  38 static __inline ALfloat lpFilter2P(FILTER *iir, ALuint offset, ALfloat input)
  39 {
  40     ALfloat *history = &iir->history[offset];
  41     ALfloat a = iir->coeff;
  42     ALfloat output = input;
  43
  44     output = output + (history[0]-output)*a;
  45     history[0] = output;
  46     output = output + (history[1]-output)*a;
  47     history[1] = output;
  48
  49     return output;
  50 }
  51
  52 static __inline ALfloat lpFilter1P(FILTER *iir, ALuint offset, ALfloat input)
  53 {
  54     ALfloat *history = &iir->history[offset];
  55     ALfloat a = iir->coeff;
  56     ALfloat output = input;
  57
  58     output = output + (history[0]-output)*a;
  59     history[0] = output;
  60
  61     return output;
  62 }
  63
  64 /* Calculates the low-pass filter coefficient given the pre-scaled gain and
  65  * cos(w) value. Note that g should be pre-scaled (sqr(gain) for one-pole,
  66  * sqrt(gain) for four-pole, etc) */
  67 static __inline ALfloat lpCoeffCalc(ALfloat g, ALfloat cw)
  68 {
  69     ALfloat a = 0.0f;
  70
  71     /* Be careful with gains < 0.01, as that causes the coefficient
  72      * head towards 1, which will flatten the signal */
  73     g = __max(g, 0.01f);
  74     if(g < 0.9999f) /* 1-epsilon */
  75         a = (1 - g*cw - aluSqrt(2*g*(1-cw) - g*g*(1 - cw*cw))) /
  76             (1 - g);
  77
  78     return a;
  79 }
  80
  81
  82 typedef struct ALfilter
  83 {
  84     // Filter type (AL_FILTER_NULL, ...)
  85     ALenum type;
  86
  87     ALfloat Gain;
  88     ALfloat GainHF;
  89
  90     // Index to itself
  91     ALuint filter;
  92
  93     struct ALfilter *next;
  94 } ALfilter;
  95
  96
  97 ALvoid ReleaseALFilters(ALCdevice *device);
  98
  99 #ifdef __cplusplus
 100 }
 101 #endif
 102
 103 #endif