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/* Based on raylib audio_stream_effects example */
#include <lua.h>
#include <lauxlib.h>
#include <lualib.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/* gcc audioProcess.c -shared -o audioProcess.so -fPIC -llua */
// Audio effect: lowpass filter
void AudioProcessEffectLPF(void *buffer, unsigned int frames)
{
static float low[2] = { 0.0f, 0.0f };
static const float cutoff = 70.0f / 44100.0f; // 70 Hz lowpass filter
const float k = cutoff / (cutoff + 0.1591549431f); // RC filter formula
// Converts the buffer data before using it
float *bufferData = (float *)buffer;
for (unsigned int i = 0; i < frames*2; i += 2)
{
const float l = bufferData[i];
const float r = bufferData[i + 1];
low[0] += k * (l - low[0]);
low[1] += k * (r - low[1]);
bufferData[i] = low[0];
bufferData[i + 1] = low[1];
}
}
static float *delayBuffer = NULL;
static unsigned int delayBufferSize = 0;
static unsigned int delayReadIndex = 2;
static unsigned int delayWriteIndex = 0;
// Audio effect: delay
static void AudioProcessEffectDelay(void *buffer, unsigned int frames)
{
for (unsigned int i = 0; i < frames*2; i += 2)
{
float leftDelay = delayBuffer[delayReadIndex++]; // ERROR: Reading buffer -> WHY??? Maybe thread related???
float rightDelay = delayBuffer[delayReadIndex++];
if (delayReadIndex == delayBufferSize) delayReadIndex = 0;
((float *)buffer)[i] = 0.5f*((float *)buffer)[i] + 0.5f*leftDelay;
((float *)buffer)[i + 1] = 0.5f*((float *)buffer)[i + 1] + 0.5f*rightDelay;
delayBuffer[delayWriteIndex++] = ((float *)buffer)[i];
delayBuffer[delayWriteIndex++] = ((float *)buffer)[i + 1];
if (delayWriteIndex == delayBufferSize) delayWriteIndex = 0;
}
}
/* API. */
static int apInit( lua_State* L ) {
// Allocate buffer for the delay effect
delayBufferSize = 48000*2; // 1 second delay (device sampleRate*channels)
delayBuffer = (float *)calloc(delayBufferSize, sizeof(float));
return 0;
}
static int getAudioProcessEffectLPF( lua_State* L ) {
lua_pushlightuserdata( L, AudioProcessEffectLPF );
return 1;
}
static int getAudioProcessEffectDelay( lua_State* L ) {
lua_pushlightuserdata( L, AudioProcessEffectDelay );
return 1;
}
static int apFree( lua_State* L ) {
free(delayBuffer); // Free delay buffer
return 0;
}
static const luaL_Reg audioProcess[] = {
{ "init", apInit },
{ "AudioProcessEffectLPF", getAudioProcessEffectLPF },
{ "AudioProcessEffectDelay", getAudioProcessEffectDelay },
{ "free", apFree },
{ NULL, NULL } // sentinel.
};
int luaopen_audioProcess(lua_State *L) {
#if LUA_VERSION_NUM <= 501
luaL_openlib( L, "audioProcess", audioProcess, 0 );
#else
luaL_newlib( L, audioProcess );
#endif
return 1;
}
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