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/**
* OpenAL cross platform audio library
* Copyright (C) 2009 by Chris Robinson.
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public
* License along with this library; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 02111-1307, USA.
* Or go to http://www.gnu.org/copyleft/lgpl.html
*/
#include "config.h"
#include <math.h>
#include <stdlib.h>
#include "AL/al.h"
#include "alFilter.h"
#include "alAuxEffectSlot.h"
#include "alEcho.h"
#include "alu.h"
struct ALechoState {
ALfloat *SampleBuffer;
ALuint BufferLength;
// The echo is two tap. The third tap is the offset to write the feedback
// and input sample to
struct {
ALuint offset;
} Tap[3];
// The LR gains for the first tap. The second tap uses the reverse
ALfloat GainL;
ALfloat GainR;
ALfloat FeedGain;
FILTER iirFilter;
ALfloat history[2];
};
// Find the next power of 2. Actually, this will return the input value if
// it is already a power of 2.
static ALuint NextPowerOf2(ALuint value)
{
ALuint powerOf2 = 1;
if(value)
{
value--;
while(value)
{
value >>= 1;
powerOf2 <<= 1;
}
}
return powerOf2;
}
ALechoState *EchoCreate(ALCcontext *Context)
{
ALechoState *state;
ALuint i, maxlen;
state = malloc(sizeof(*state));
if(!state)
return NULL;
maxlen = (ALuint)(AL_ECHO_MAX_DELAY * Context->Frequency);
maxlen += (ALuint)(AL_ECHO_MAX_LRDELAY * Context->Frequency);
// Use the next power of 2 for the buffer length, so the tap offsets can be
// wrapped using a mask instead of a modulo
state->BufferLength = NextPowerOf2(maxlen+1);
state->SampleBuffer = malloc(state->BufferLength * sizeof(ALfloat));
if(!state->SampleBuffer)
{
free(state);
return NULL;
}
for(i = 0;i < state->BufferLength;i++)
state->SampleBuffer[i] = 0.0f;
state->Tap[0].offset = 0;
state->Tap[1].offset = 0;
state->Tap[2].offset = 0;
state->GainL = 0.0f;
state->GainR = 0.0f;
for(i = 0;i < sizeof(state->history)/sizeof(state->history[0]);i++)
state->history[i] = 0.0f;
state->iirFilter.coeff = 0.0f;
return state;
}
ALvoid EchoDestroy(ALechoState *state)
{
if(state)
{
free(state->SampleBuffer);
state->SampleBuffer = NULL;
free(state);
}
}
ALvoid EchoUpdate(ALCcontext *Context, struct ALeffectslot *Slot, ALeffect *Effect)
{
ALechoState *state = Slot->EchoState;
ALuint newdelay1, newdelay2;
ALfloat lrpan, cw, a, g;
newdelay1 = (ALuint)(Effect->Echo.Delay * Context->Frequency);
newdelay2 = (ALuint)(Effect->Echo.LRDelay * Context->Frequency);
state->Tap[0].offset = (state->BufferLength - newdelay1 - 1 +
state->Tap[2].offset)%state->BufferLength;
state->Tap[1].offset = (state->BufferLength - newdelay1 - newdelay2 - 1 +
state->Tap[2].offset)%state->BufferLength;
lrpan = Effect->Echo.Spread*0.5f + 0.5f;
state->GainL = aluSqrt( lrpan);
state->GainR = aluSqrt(1.0f-lrpan);
state->FeedGain = Effect->Echo.Feedback;
cw = cos(2.0*M_PI * LOWPASSFREQCUTOFF / Context->Frequency);
g = 1.0f - Effect->Echo.Damping;
a = 0.0f;
if(g < 0.9999f) // 1-epsilon
a = (1 - g*cw - aluSqrt(2*g*(1-cw) - g*g*(1 - cw*cw))) / (1 - g);
state->iirFilter.coeff = a;
}
ALvoid EchoProcess(ALechoState *state, ALuint SamplesToDo, const ALfloat *SamplesIn, ALfloat (*SamplesOut)[OUTPUTCHANNELS])
{
ALfloat *history = state->iirFilter.history;
const ALfloat a = state->iirFilter.coeff;
const ALuint delay = state->BufferLength-1;
ALuint tap1off = state->Tap[0].offset;
ALuint tap2off = state->Tap[1].offset;
ALuint fboff = state->Tap[2].offset;
ALfloat samp[2];
ALuint i;
for(i = 0;i < SamplesToDo;i++)
{
// Apply damping
samp[0] = state->SampleBuffer[tap2off] + SamplesIn[i];
samp[0] += (history[0]-samp[0]) * a;
history[0] = samp[0];
samp[0] += (history[1]-samp[0]) * a;
history[1] = samp[0];
// Apply feedback gain and mix in the new sample
state->SampleBuffer[fboff] = samp[0] * state->FeedGain;
tap1off = (tap1off+1) & delay;
tap2off = (tap2off+1) & delay;
fboff = (fboff+1) & delay;
// Sample first tap
samp[0] = state->SampleBuffer[tap1off]*state->GainL;
samp[1] = state->SampleBuffer[tap1off]*state->GainR;
// Sample second tap. Reverse LR panning
samp[0] += state->SampleBuffer[tap2off]*state->GainR;
samp[1] += state->SampleBuffer[tap2off]*state->GainL;
SamplesOut[i][FRONT_LEFT] += samp[0];
SamplesOut[i][FRONT_RIGHT] += samp[1];
SamplesOut[i][SIDE_LEFT] += samp[0];
SamplesOut[i][SIDE_RIGHT] += samp[1];
SamplesOut[i][BACK_LEFT] += samp[0];
SamplesOut[i][BACK_RIGHT] += samp[1];
}
state->Tap[0].offset = tap1off;
state->Tap[1].offset = tap2off;
state->Tap[2].offset = fboff;
}
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