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     ALfloat Gain[OUTPUTCHANNELS];
  53
  54     FILTER iirFilter;
  55     ALfloat history[2];
  56 } ALechoState;
  57
  58 static ALvoid EchoDestroy(ALeffectState *effect)
  59 {
  60     ALechoState *state = (ALechoState*)effect;
  61     if(state)
  62     {
  63         free(state->SampleBuffer);
  64         state->SampleBuffer = NULL;
  65         free(state);
  66     }
  67 }
  68
  69 static ALboolean EchoDeviceUpdate(ALeffectState *effect, ALCdevice *Device)
  70 {
  71     ALechoState *state = (ALechoState*)effect;
  72     ALuint maxlen, i;
  73
  74     // Use the next power of 2 for the buffer length, so the tap offsets can be
  75     // wrapped using a mask instead of a modulo
  76     maxlen  = (ALuint)(AL_ECHO_MAX_DELAY * Device->Frequency) + 1;
  77     maxlen += (ALuint)(AL_ECHO_MAX_LRDELAY * Device->Frequency) + 1;
  78     maxlen  = NextPowerOf2(maxlen);
  79
  80     if(maxlen != state->BufferLength)
  81     {
  82         void *temp;
  83
  84         temp = realloc(state->SampleBuffer, maxlen * sizeof(ALfloat));
  85         if(!temp)
  86             return AL_FALSE;
  87         state->SampleBuffer = temp;
  88         state->BufferLength = maxlen;
  89     }
  90     for(i = 0;i < state->BufferLength;i++)
  91         state->SampleBuffer[i] = 0.0f;
  92
  93     for(i = 0;i < OUTPUTCHANNELS;i++)
  94         state->Gain[i] = 0.0f;
  95     for(i = 0;i < Device->NumChan;i++)
  96     {
  97         Channel chan = Device->Speaker2Chan[i];
  98         state->Gain[chan] = 1.0f;
  99     }
 100
 101     return AL_TRUE;
 102 }
 103
 104 static ALvoid EchoUpdate(ALeffectState *effect, ALCcontext *Context, const ALeffect *Effect)
 105 {
 106     ALechoState *state = (ALechoState*)effect;
 107     ALuint frequency = Context->Device->Frequency;
 108     ALfloat lrpan, cw, a, g;
 109
 110     state->Tap[0].delay = (ALuint)(Effect->Echo.Delay * frequency) + 1;
 111     state->Tap[1].delay = (ALuint)(Effect->Echo.LRDelay * frequency);
 112     state->Tap[1].delay += state->Tap[0].delay;
 113
 114     lrpan = Effect->Echo.Spread*0.5f + 0.5f;
 115     state->GainL = aluSqrt(     lrpan);
 116     state->GainR = aluSqrt(1.0f-lrpan);
 117
 118     state->FeedGain = Effect->Echo.Feedback;
 119
 120     cw = cos(2.0*M_PI * LOWPASSFREQCUTOFF / frequency);
 121     g = 1.0f - Effect->Echo.Damping;
 122     a = 0.0f;
 123     if(g < 0.9999f) // 1-epsilon
 124         a = (1 - g*cw - aluSqrt(2*g*(1-cw) - g*g*(1 - cw*cw))) / (1 - g);
 125     state->iirFilter.coeff = a;
 126 }
 127
 128 static ALvoid EchoProcess(ALeffectState *effect, const ALeffectslot *Slot, ALuint SamplesToDo, const ALfloat *SamplesIn, ALfloat (*SamplesOut)[OUTPUTCHANNELS])
 129 {
 130     ALechoState *state = (ALechoState*)effect;
 131     const ALuint mask = state->BufferLength-1;
 132     const ALuint tap1 = state->Tap[0].delay;
 133     const ALuint tap2 = state->Tap[1].delay;
 134     ALuint offset = state->Offset;
 135     const ALfloat gain = Slot->Gain;
 136     ALfloat samp[2], smp;
 137     ALuint i;
 138
 139     for(i = 0;i < SamplesToDo;i++,offset++)
 140     {
 141         // Sample first tap
 142         smp = state->SampleBuffer[(offset-tap1) & mask];
 143         samp[0] = smp * state->GainL;
 144         samp[1] = smp * state->GainR;
 145         // Sample second tap. Reverse LR panning
 146         smp = state->SampleBuffer[(offset-tap2) & mask];
 147         samp[0] += smp * state->GainR;
 148         samp[1] += smp * state->GainL;
 149
 150         // Apply damping and feedback gain to the second tap, and mix in the
 151         // new sample
 152         smp = lpFilter2P(&state->iirFilter, 0, smp+SamplesIn[i]);
 153         state->SampleBuffer[offset&mask] = smp * state->FeedGain;
 154
 155         // Apply slot gain
 156         samp[0] *= gain;
 157         samp[1] *= gain;
 158
 159         SamplesOut[i][FRONT_LEFT]  += state->Gain[FRONT_LEFT]  * samp[0];
 160         SamplesOut[i][FRONT_RIGHT] += state->Gain[FRONT_RIGHT] * samp[1];
 161         SamplesOut[i][SIDE_LEFT]   += state->Gain[SIDE_LEFT]   * samp[0];
 162         SamplesOut[i][SIDE_RIGHT]  += state->Gain[SIDE_RIGHT]  * samp[1];
 163         SamplesOut[i][BACK_LEFT]   += state->Gain[BACK_LEFT]   * samp[0];
 164         SamplesOut[i][BACK_RIGHT]  += state->Gain[BACK_RIGHT]  * samp[1];
 165     }
 166     state->Offset = offset;
 167 }
 168
 169 ALeffectState *EchoCreate(void)
 170 {
 171     ALechoState *state;
 172
 173     state = malloc(sizeof(*state));
 174     if(!state)
 175         return NULL;
 176
 177     state->state.Destroy = EchoDestroy;
 178     state->state.DeviceUpdate = EchoDeviceUpdate;
 179     state->state.Update = EchoUpdate;
 180     state->state.Process = EchoProcess;
 181
 182     state->BufferLength = 0;
 183     state->SampleBuffer = NULL;
 184
 185     state->Tap[0].delay = 0;
 186     state->Tap[1].delay = 0;
 187     state->Offset = 0;
 188     state->GainL = 0.0f;
 189     state->GainR = 0.0f;
 190
 191     state->iirFilter.coeff = 0.0f;
 192     state->iirFilter.history[0] = 0.0f;
 193     state->iirFilter.history[1] = 0.0f;
 194
 195     return &state->state;
 196 }