Add the Echo effect

1 files changed, 194 insertions, 0 deletions

diff --git a/Alc/alcEcho.c b/Alc/alcEcho.c
new file mode 100644
index 00000000..6640d9af
--- /dev/null
+++ b/Alc/alcEcho.c
@@ -0,0 +1,194 @@
+/**
+ * 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"
+
+#ifdef HAVE_SQRTF
+#define aluSqrt(x) ((ALfloat)sqrtf((float)(x)))
+#else
+#define aluSqrt(x) ((ALfloat)sqrt((double)(x)))
+#endif
+
+struct ALechoState {
+    ALfloat *SampleBuffer;
+    ALuint BufferLength;
+
+    // The echo is two tap. The third tap is the offset to sample from for
+    // feedback
+    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;
+};
+
+// 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->iirFilter.history)/sizeof(state->iirFilter.history[0]);i++)
+        state->iirFilter.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;
+}