Implement yet another low-pass filter

This one using the Butterworth IIR filter design

5 files changed, 24 insertions, 2 deletions

diff --git a/OpenAL32/Include/alAuxEffectSlot.h b/OpenAL32/Include/alAuxEffectSlot.h
index d4cb0d11..9bae788d 100644
--- a/OpenAL32/Include/alAuxEffectSlot.h
+++ b/OpenAL32/Include/alAuxEffectSlot.h
@@ -1,8 +1,9 @@
 #ifndef _AL_AUXEFFECTSLOT_H_
 #define _AL_AUXEFFECTSLOT_H_
 
-#include "alEffect.h"
 #include "AL/al.h"
+#include "alEffect.h"
+#include "alFilter.h"
 
 #ifdef __cplusplus
 extern "C" {
@@ -28,7 +29,8 @@ typedef struct ALeffectslot
     ALuint ReverbReflectPos;
     ALuint ReverbLatePos;
     ALfloat ReverbDecayGain;
-    ALfloat LastDecaySample;
+
+    FILTER iirFilter;
 
     ALuint refcount;
 
diff --git a/OpenAL32/Include/alFilter.h b/OpenAL32/Include/alFilter.h
index 038304e8..f1d24d0f 100644
--- a/OpenAL32/Include/alFilter.h
+++ b/OpenAL32/Include/alFilter.h
@@ -7,6 +7,11 @@
 extern "C" {
 #endif
 
+typedef struct {
+    float *history; /* pointer to history in filter */
+    float *coef;    /* pointer to coefficients of filter */
+} FILTER;
+
 #define AL_FILTER_TYPE                                     0x8001
 
 #define AL_FILTER_NULL                                     0x0000
@@ -48,6 +53,9 @@ AL_API ALvoid AL_APIENTRY alGetFilterfv(ALuint filter, ALenum param, ALfloat *pf
 
 ALvoid ReleaseALFilters(ALvoid);
 
+float lpFilter(FILTER *iir, float input);
+int InitLowPassFilter(ALCcontext *Context, FILTER *iir);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/OpenAL32/Include/alSource.h b/OpenAL32/Include/alSource.h
index 1d3fc57c..73b02609 100644
--- a/OpenAL32/Include/alSource.h
+++ b/OpenAL32/Include/alSource.h
@@ -75,6 +75,8 @@ typedef struct ALsource
     ALboolean WetGainHFAuto;
     ALfloat   OuterGainHF;
 
+    FILTER iirFilter;
+
     ALfloat AirAbsorptionFactor;
 
     ALfloat RoomRolloffFactor;
diff --git a/OpenAL32/alAuxEffectSlot.c b/OpenAL32/alAuxEffectSlot.c
index 23765cf6..e05448cd 100644
--- a/OpenAL32/alAuxEffectSlot.c
+++ b/OpenAL32/alAuxEffectSlot.c
@@ -71,6 +71,8 @@ AL_API ALvoid AL_APIENTRY alGenAuxiliaryEffectSlots(ALsizei n, ALuint *effectslo
                         break;
                     }
 
+                    InitLowPassFilter(Context, &(*list)->iirFilter);
+
                     (*list)->Gain = 1.0;
                     (*list)->AuxSendAuto = AL_TRUE;
                     (*list)->refcount = 0;
@@ -139,6 +141,9 @@ AL_API ALvoid AL_APIENTRY alDeleteAuxiliaryEffectSlots(ALsizei n, ALuint *effect
 
                     ALAuxiliaryEffectSlot = ((ALeffectslot*)ALTHUNK_LOOKUPENTRY(effectslots[i]));
 
+                    free(ALAuxiliaryEffectSlot->iirFilter.coef);
+                    free(ALAuxiliaryEffectSlot->iirFilter.history);
+
                     // Remove Source from list of Sources
                     list = &Context->AuxiliaryEffectSlot;
                     while(*list && *list != ALAuxiliaryEffectSlot)
diff --git a/OpenAL32/alSource.c b/OpenAL32/alSource.c
index 89212933..1960b676 100644
--- a/OpenAL32/alSource.c
+++ b/OpenAL32/alSource.c
@@ -75,6 +75,8 @@ ALAPI ALvoid ALAPIENTRY alGenSources(ALsizei n,ALuint *sources)
                                 break;
                             }
 
+                            InitLowPassFilter(Context, &(*list)->iirFilter);
+
                             sources[i] = (ALuint)ALTHUNK_ADDENTRY(*list);
                             (*list)->source = sources[i];
 
@@ -179,6 +181,9 @@ ALAPI ALvoid ALAPIENTRY alDeleteSources(ALsizei n, const ALuint *sources)
                                 ALSource->Send[j].Slot = NULL;
                             }
 
+                            free(ALSource->iirFilter.coef);
+                            free(ALSource->iirFilter.history);
+
                             // Decrement Source count
                             Context->SourceCount--;