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 static __inline ALfloat lpFilter4PC(const FILTER *iir, ALuint offset, ALfloat input)
  65 {
  66     const ALfloat *history = &iir->history[offset];
  67     ALfloat a = iir->coeff;
  68     ALfloat output = input;
  69
  70     output = output + (history[0]-output)*a;
  71     output = output + (history[1]-output)*a;
  72     output = output + (history[2]-output)*a;
  73     output = output + (history[3]-output)*a;
  74
  75     return output;
  76 }
  77
  78 static __inline ALfloat lpFilter2PC(const FILTER *iir, ALuint offset, ALfloat input)
  79 {
  80     const ALfloat *history = &iir->history[offset];
  81     ALfloat a = iir->coeff;
  82     ALfloat output = input;
  83
  84     output = output + (history[0]-output)*a;
  85     output = output + (history[1]-output)*a;
  86
  87     return output;
  88 }
  89
  90 static __inline ALfloat lpFilter1PC(FILTER *iir, ALuint offset, ALfloat input)
  91 {
  92     const ALfloat *history = &iir->history[offset];
  93     ALfloat a = iir->coeff;
  94     ALfloat output = input;
  95
  96     output = output + (history[0]-output)*a;
  97
  98     return output;
  99 }
 100
 101 /* Calculates the low-pass filter coefficient given the pre-scaled gain and
 102  * cos(w) value. Note that g should be pre-scaled (sqr(gain) for one-pole,
 103  * sqrt(gain) for four-pole, etc) */
 104 static __inline ALfloat lpCoeffCalc(ALfloat g, ALfloat cw)
 105 {
 106     ALfloat a = 0.0f;
 107
 108     /* Be careful with gains < 0.01, as that causes the coefficient
 109      * head towards 1, which will flatten the signal */
 110     g = __max(g, 0.01f);
 111     if(g < 0.9999f) /* 1-epsilon */
 112         a = (1 - g*cw - aluSqrt(2*g*(1-cw) - g*g*(1 - cw*cw))) /
 113             (1 - g);
 114
 115     return a;
 116 }
 117
 118
 119 typedef struct ALfilter
 120 {
 121     // Filter type (AL_FILTER_NULL, ...)
 122     ALenum type;
 123
 124     ALfloat Gain;
 125     ALfloat GainHF;
 126
 127     // Index to itself
 128     ALuint filter;
 129 } ALfilter;
 130
 131
 132 ALvoid ReleaseALFilters(ALCdevice *device);
 133
 134 #ifdef __cplusplus
 135 }
 136 #endif
 137
 138 #endif