From 3bedd89e1dddda12bbe14040d23cbf7b169ab305 Mon Sep 17 00:00:00 2001
From: jussi
Date: Mon, 8 Sep 2025 22:36:40 +0300
Subject: AudioStream management functions.

---
 examples/resources/clib/audioProcess.c | 100 +++++++++++++++++++++++++++++++++
 1 file changed, 100 insertions(+)
 create mode 100644 examples/resources/clib/audioProcess.c

(limited to 'examples/resources/clib/audioProcess.c')

diff --git a/examples/resources/clib/audioProcess.c b/examples/resources/clib/audioProcess.c
new file mode 100644
index 0000000..ad18117
--- /dev/null
+++ b/examples/resources/clib/audioProcess.c
@@ -0,0 +1,100 @@
+/* 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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