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
  33 typedef struct ALechoState {
  34     // Must be first in all effects!
  35     ALeffectState state;
  36
  37     ALfloat *SampleBuffer;
  38     ALuint BufferLength;
  39
  40     // The echo is two tap. The delay is the number of samples from before the
  41     // current offset
  42     struct {
  43         ALuint delay;
  44     } Tap[2];
  45     ALuint Offset;
  46     // The LR gains for the first tap. The second tap uses the reverse
  47     ALfloat GainL;
  48     ALfloat GainR;
  49
  50     ALfloat FeedGain;
  51
  52     FILTER iirFilter;
  53     ALfloat history[2];
  54 } ALechoState;
  55
  56 ALvoid EchoDestroy(ALeffectState *effect)
  57 {
  58     ALechoState *state = (ALechoState*)effect;
  59     if(state)
  60     {
  61         free(state->SampleBuffer);
  62         state->SampleBuffer = NULL;
  63         free(state);
  64     }
  65 }
  66
  67 ALboolean EchoDeviceUpdate(ALeffectState *effect, ALCdevice *Device)
  68 {
  69     ALechoState *state = (ALechoState*)effect;
  70     ALuint maxlen, i;
  71
  72     // Use the next power of 2 for the buffer length, so the tap offsets can be
  73     // wrapped using a mask instead of a modulo
  74     maxlen  = (ALuint)(AL_ECHO_MAX_DELAY * Device->Frequency) + 1;
  75     maxlen += (ALuint)(AL_ECHO_MAX_LRDELAY * Device->Frequency) + 1;
  76     maxlen  = NextPowerOf2(maxlen);
  77
  78     if(maxlen != state->BufferLength)
  79     {
  80         void *temp;
  81
  82         temp = realloc(state->SampleBuffer, maxlen * sizeof(ALfloat));
  83         if(!temp)
  84         {
  85             alSetError(AL_OUT_OF_MEMORY);
  86             return AL_FALSE;
  87         }
  88         state->SampleBuffer = temp;
  89         state->BufferLength = maxlen;
  90     }
  91     for(i = 0;i < state->BufferLength;i++)
  92         state->SampleBuffer[i] = 0.0f;
  93
  94     return AL_TRUE;
  95 }
  96
  97 ALvoid EchoUpdate(ALeffectState *effect, ALCcontext *Context, const ALeffect *Effect)
  98 {
  99     ALechoState *state = (ALechoState*)effect;
 100     ALuint frequency = Context->Device->Frequency;
 101     ALfloat lrpan, cw, a, g;
 102
 103     state->Tap[0].delay = (ALuint)(Effect->Echo.Delay * frequency) + 1;
 104     state->Tap[1].delay = (ALuint)(Effect->Echo.LRDelay * frequency);
 105     state->Tap[1].delay += state->Tap[0].delay;
 106
 107     lrpan = Effect->Echo.Spread*0.5f + 0.5f;
 108     state->GainL = aluSqrt(     lrpan);
 109     state->GainR = aluSqrt(1.0f-lrpan);
 110
 111     state->FeedGain = Effect->Echo.Feedback;
 112
 113     cw = cos(2.0*M_PI * LOWPASSFREQCUTOFF / frequency);
 114     g = 1.0f - Effect->Echo.Damping;
 115     a = 0.0f;
 116     if(g < 0.9999f) // 1-epsilon
 117         a = (1 - g*cw - aluSqrt(2*g*(1-cw) - g*g*(1 - cw*cw))) / (1 - g);
 118     state->iirFilter.coeff = a;
 119 }
 120
 121 ALvoid EchoProcess(ALeffectState *effect, const ALeffectslot *Slot, ALuint SamplesToDo, const ALfloat *SamplesIn, ALfloat (*SamplesOut)[OUTPUTCHANNELS])
 122 {
 123     ALechoState *state = (ALechoState*)effect;
 124     const ALuint mask = state->BufferLength-1;
 125     const ALuint tap1 = state->Tap[0].delay;
 126     const ALuint tap2 = state->Tap[1].delay;
 127     ALuint offset = state->Offset;
 128     const ALfloat gain = Slot->Gain;
 129     ALfloat samp[2], smp;
 130     ALuint i;
 131
 132     for(i = 0;i < SamplesToDo;i++,offset++)
 133     {
 134         // Sample first tap
 135         smp = state->SampleBuffer[(offset-tap1) & mask];
 136         samp[0] = smp * state->GainL;
 137         samp[1] = smp * state->GainR;
 138         // Sample second tap. Reverse LR panning
 139         smp = state->SampleBuffer[(offset-tap2) & mask];
 140         samp[0] += smp * state->GainR;
 141         samp[1] += smp * state->GainL;
 142
 143         // Apply damping and feedback gain to the second tap, and mix in the
 144         // new sample
 145         smp = lpFilter2P(&state->iirFilter, 0, smp+SamplesIn[i]);
 146         state->SampleBuffer[offset&mask] = smp * state->FeedGain;
 147
 148         // Apply slot gain
 149         samp[0] *= gain;
 150         samp[1] *= gain;
 151
 152         SamplesOut[i][FRONT_LEFT]  += samp[0];
 153         SamplesOut[i][FRONT_RIGHT] += samp[1];
 154         SamplesOut[i][SIDE_LEFT]   += samp[0];
 155         SamplesOut[i][SIDE_RIGHT]  += samp[1];
 156         SamplesOut[i][BACK_LEFT]   += samp[0];
 157         SamplesOut[i][BACK_RIGHT]  += samp[1];
 158     }
 159     state->Offset = offset;
 160 }
 161
 162 ALeffectState *EchoCreate(void)
 163 {
 164     ALechoState *state;
 165
 166     state = malloc(sizeof(*state));
 167     if(!state)
 168     {
 169         alSetError(AL_OUT_OF_MEMORY);
 170         return NULL;
 171     }
 172
 173     state->state.Destroy = EchoDestroy;
 174     state->state.DeviceUpdate = EchoDeviceUpdate;
 175     state->state.Update = EchoUpdate;
 176     state->state.Process = EchoProcess;
 177
 178     state->BufferLength = 0;
 179     state->SampleBuffer = NULL;
 180
 181     state->Tap[0].delay = 0;
 182     state->Tap[1].delay = 0;
 183     state->Offset = 0;
 184     state->GainL = 0.0f;
 185     state->GainR = 0.0f;
 186
 187     state->iirFilter.coeff = 0.0f;
 188     state->iirFilter.history[0] = 0.0f;
 189     state->iirFilter.history[1] = 0.0f;
 190
 191     return &state->state;
 192 }