Alc/alcEcho.c

   1 /**
   2  * OpenAL cross platform audio library
   3  * Copyright (C) 2009 by Chris Robinson.
   4  * This library is free software; you can redistribute it and/or
   5  *  modify it under the terms of the GNU Library General Public
   6  *  License as published by the Free Software Foundation; either
   7  *  version 2 of the License, or (at your option) any later version.
   8  *
   9  * This library is distributed in the hope that it will be useful,
  10  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  *  Library General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU Library General Public
  15  *  License along with this library; if not, write to the
  16  *  Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  17  *  Boston, MA  02111-1307, USA.
  18  * Or go to http://www.gnu.org/copyleft/lgpl.html
  19  */
  20
  21 #include "config.h"
  22
  23 #include <math.h>
  24 #include <stdlib.h>
  25
  26 #include "alMain.h"
  27 #include "alFilter.h"
  28 #include "alAuxEffectSlot.h"
  29 #include "alError.h"
  30 #include "alu.h"
  31
  32 typedef struct ALechoState {
  33     // Must be first in all effects!
  34     ALeffectState state;
  35
  36     ALfloat *SampleBuffer;
  37     ALuint BufferLength;
  38
  39     // The echo is two tap. The third tap is the offset to write the feedback
  40     // and input sample to
  41     struct {
  42         ALuint offset;
  43     } Tap[3];
  44     // The LR gains for the first tap. The second tap uses the reverse
  45     ALfloat GainL;
  46     ALfloat GainR;
  47
  48     ALfloat FeedGain;
  49
  50     FILTER iirFilter;
  51     ALfloat history[2];
  52 } ALechoState;
  53
  54 // Find the next power of 2.  Actually, this will return the input value if
  55 // it is already a power of 2.
  56 static ALuint NextPowerOf2(ALuint value)
  57 {
  58     ALuint powerOf2 = 1;
  59
  60     if(value)
  61     {
  62         value--;
  63         while(value)
  64         {
  65             value >>= 1;
  66             powerOf2 <<= 1;
  67         }
  68     }
  69     return powerOf2;
  70 }
  71
  72 ALvoid EchoDestroy(ALeffectState *effect)
  73 {
  74     ALechoState *state = (ALechoState*)effect;
  75     if(state)
  76     {
  77         free(state->SampleBuffer);
  78         state->SampleBuffer = NULL;
  79         free(state);
  80     }
  81 }
  82
  83 ALvoid EchoUpdate(ALeffectState *effect, ALCcontext *Context, ALeffect *Effect)
  84 {
  85     ALechoState *state = (ALechoState*)effect;
  86     ALuint newdelay1, newdelay2;
  87     ALfloat lrpan, cw, a, g;
  88
  89     newdelay1 = (ALuint)(Effect->Echo.Delay * Context->Frequency);
  90     newdelay2 = (ALuint)(Effect->Echo.LRDelay * Context->Frequency);
  91
  92     state->Tap[0].offset = (state->BufferLength - newdelay1 - 1 +
  93                             state->Tap[2].offset)%state->BufferLength;
  94     state->Tap[1].offset = (state->BufferLength - newdelay1 - newdelay2 - 1 +
  95                             state->Tap[2].offset)%state->BufferLength;
  96
  97     lrpan = Effect->Echo.Spread*0.5f + 0.5f;
  98     state->GainL = aluSqrt(     lrpan);
  99     state->GainR = aluSqrt(1.0f-lrpan);
 100
 101     state->FeedGain = Effect->Echo.Feedback;
 102
 103     cw = cos(2.0*M_PI * LOWPASSFREQCUTOFF / Context->Frequency);
 104     g = 1.0f - Effect->Echo.Damping;
 105     a = 0.0f;
 106     if(g < 0.9999f) // 1-epsilon
 107         a = (1 - g*cw - aluSqrt(2*g*(1-cw) - g*g*(1 - cw*cw))) / (1 - g);
 108     state->iirFilter.coeff = a;
 109 }
 110
 111 ALvoid EchoProcess(ALeffectState *effect, const ALeffectslot *Slot, ALuint SamplesToDo, const ALfloat *SamplesIn, ALfloat (*SamplesOut)[OUTPUTCHANNELS])
 112 {
 113     ALechoState *state = (ALechoState*)effect;
 114     const ALuint delay = state->BufferLength-1;
 115     ALuint tap1off = state->Tap[0].offset;
 116     ALuint tap2off = state->Tap[1].offset;
 117     ALuint fboff = state->Tap[2].offset;
 118     ALfloat gain = Slot->Gain;
 119     ALfloat samp[2];
 120     ALuint i;
 121
 122     for(i = 0;i < SamplesToDo;i++)
 123     {
 124         // Apply damping
 125         samp[0] = lpFilter2P(&state->iirFilter, 0, state->SampleBuffer[tap2off]+SamplesIn[i]);
 126
 127         // Apply feedback gain and mix in the new sample
 128         state->SampleBuffer[fboff] = samp[0] * state->FeedGain;
 129
 130         tap1off = (tap1off+1) & delay;
 131         tap2off = (tap2off+1) & delay;
 132         fboff = (fboff+1) & delay;
 133
 134         // Sample first tap
 135         samp[0] = state->SampleBuffer[tap1off]*state->GainL;
 136         samp[1] = state->SampleBuffer[tap1off]*state->GainR;
 137         // Sample second tap. Reverse LR panning
 138         samp[0] += state->SampleBuffer[tap2off]*state->GainR;
 139         samp[1] += state->SampleBuffer[tap2off]*state->GainL;
 140         // Apply slot gain
 141         samp[0] *= gain;
 142         samp[1] *= gain;
 143
 144         SamplesOut[i][FRONT_LEFT]  += samp[0];
 145         SamplesOut[i][FRONT_RIGHT] += samp[1];
 146         SamplesOut[i][SIDE_LEFT]   += samp[0];
 147         SamplesOut[i][SIDE_RIGHT]  += samp[1];
 148         SamplesOut[i][BACK_LEFT]   += samp[0];
 149         SamplesOut[i][BACK_RIGHT]  += samp[1];
 150     }
 151
 152     state->Tap[0].offset = tap1off;
 153     state->Tap[1].offset = tap2off;
 154     state->Tap[2].offset = fboff;
 155 }
 156
 157 ALeffectState *EchoCreate(ALCcontext *Context)
 158 {
 159     ALechoState *state;
 160     ALuint i, maxlen;
 161
 162     state = malloc(sizeof(*state));
 163     if(!state)
 164     {
 165         alSetError(AL_OUT_OF_MEMORY);
 166         return NULL;
 167     }
 168
 169     state->state.Destroy = EchoDestroy;
 170     state->state.Update = EchoUpdate;
 171     state->state.Process = EchoProcess;
 172
 173     maxlen  = (ALuint)(AL_ECHO_MAX_DELAY * Context->Frequency);
 174     maxlen += (ALuint)(AL_ECHO_MAX_LRDELAY * Context->Frequency);
 175
 176     // Use the next power of 2 for the buffer length, so the tap offsets can be
 177     // wrapped using a mask instead of a modulo
 178     state->BufferLength = NextPowerOf2(maxlen+1);
 179     state->SampleBuffer = malloc(state->BufferLength * sizeof(ALfloat));
 180     if(!state->SampleBuffer)
 181     {
 182         free(state);
 183         alSetError(AL_OUT_OF_MEMORY);
 184         return NULL;
 185     }
 186
 187     for(i = 0;i < state->BufferLength;i++)
 188         state->SampleBuffer[i] = 0.0f;
 189
 190     state->Tap[0].offset = 0;
 191     state->Tap[1].offset = 0;
 192     state->Tap[2].offset = 0;
 193     state->GainL = 0.0f;
 194     state->GainR = 0.0f;
 195
 196     for(i = 0;i < 2;i++)
 197         state->iirFilter.history[i] = 0.0f;
 198     state->iirFilter.coeff = 0.0f;
 199
 200     return &state->state;
 201 }