ADDED: Audio stream processors support -WIP- #2212

This feature is still under consideration/testing and it doesn't work properly, at least the Delay Effect processor.

examples/audio/audio_music_stream.c

@@ -11,6 +11,47 @@
 
 #include "raylib.h"
 
+// Audio effect: lowpass filter
+static void AudioProcessEffectLPF(float *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
+
+    for (unsigned int i = 0; i < frames*2; i += 2)
+    {
+        float l = buffer[i], r = buffer[i + 1];
+        low[0] += k * (l - low[0]);
+        low[1] += k * (r - low[1]);
+        buffer[i] = low[0];
+        buffer[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(float *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;
+
+        buffer[i] = 0.5f*buffer[i] + 0.5f*leftDelay;
+        buffer[i + 1] = 0.5f*buffer[i + 1] + 0.5f*rightDelay;
+
+        delayBuffer[delayWriteIndex++] = buffer[i];
+        delayBuffer[delayWriteIndex++] = buffer[i + 1];
+        if (delayWriteIndex == delayBufferSize) delayWriteIndex = 0;
+    }
+}
+
 int main(void)
 {
     // Initialization
@@ -24,11 +65,17 @@ int main(void)
 
     Music music = LoadMusicStream("resources/country.mp3");
 
+    // Allocate buffer for the delay effect
+    delayBuffer = (float *)RL_CALLOC(48000*2, sizeof(float));   // 1 second delay (device sampleRate*channels)
+
     PlayMusicStream(music);
 
     float timePlayed = 0.0f;
     bool pause = false;
 
+    bool hasFilter = false;
+    bool hasDelay = false;
+
     SetTargetFPS(60);               // Set our game to run at 60 frames-per-second
     //--------------------------------------------------------------------------------------
 
@@ -55,6 +102,22 @@ int main(void)
             else ResumeMusicStream(music);
         }
 
+        // Add/Remove effect: lowpass filter
+        if (IsKeyPressed(KEY_F))
+        {
+            hasFilter = !hasFilter;
+            if (hasFilter) AttachAudioStreamProcessor(music.stream, AudioProcessEffectLPF);
+            else DetachAudioStreamProcessor(music.stream, AudioProcessEffectLPF);
+        }
+
+        // Add/Remove effect: delay
+        if (IsKeyPressed(KEY_D))
+        {
+            hasDelay = !hasDelay;
+            if (hasDelay) AttachAudioStreamProcessor(music.stream, AudioProcessEffectDelay);
+            else DetachAudioStreamProcessor(music.stream, AudioProcessEffectDelay);
+        }
+
         // Get timePlayed scaled to bar dimensions (400 pixels)
         timePlayed = GetMusicTimePlayed(music)/GetMusicTimeLength(music)*400;
 
@@ -86,6 +149,8 @@ int main(void)
 
     CloseAudioDevice();         // Close audio device (music streaming is automatically stopped)
 
+    RL_FREE(delayBuffer);       // Free delay buffer
+
     CloseWindow();              // Close window and OpenGL context
     //--------------------------------------------------------------------------------------
 

src/raudio.c

@@ -316,6 +316,7 @@ struct rAudioBuffer {
     ma_data_converter converter;    // Audio data converter
     
     AudioCallback callback;   // Audio buffer callback for buffer filling on audio threads
+    rAudioProcessor *processor;     // Audio processor
 
     float volume;                   // Audio buffer volume
     float pitch;                    // Audio buffer pitch
@@ -337,6 +338,14 @@ struct rAudioBuffer {
     rAudioBuffer *prev;             // Previous audio buffer on the list
 };
 
+// Audio processor struct 
+// NOTE: Useful to apply effects to an AudioBuffer
+struct rAudioProcessor {
+    AudioCallback process;          // Processor callback function
+    rAudioProcessor *next;          // Next audio processor on the list
+    rAudioProcessor *prev;          // Previous audio processor on the list
+};
+
 #define AudioBuffer rAudioBuffer    // HACK: To avoid CoreAudio (macOS) symbol collision
 
 // Audio data context
@@ -559,6 +568,7 @@ AudioBuffer *LoadAudioBuffer(ma_format format, ma_uint32 channels, ma_uint32 sam
     audioBuffer->pan = 0.5f;
     
     audioBuffer->callback = NULL;
+    audioBuffer->processor = NULL;
 
     audioBuffer->playing = false;
     audioBuffer->paused = false;
@@ -2039,6 +2049,58 @@ void SetAudioStreamCallback(AudioStream stream, AudioCallback callback)
     if (stream.buffer != NULL) stream.buffer->callback = callback;
 }
 
+// Add processor to audio stream. Contrary to buffers, the order of processors is important.
+// The new processor must be added at the end. As there aren't supposed to be a lot of processors attached to
+// a given stream, we iterate through the list to find the end. That way we don't need a pointer to the last element.
+void AttachAudioStreamProcessor(AudioStream stream, AudioCallback process)
+{
+    ma_mutex_lock(&AUDIO.System.lock);
+
+    rAudioProcessor *processor = (rAudioProcessor *)RL_CALLOC(1, sizeof(rAudioProcessor));
+    processor->process = process;
+
+    rAudioProcessor *last = stream.buffer->processor;
+
+    while (last && last->next)
+    {
+        last = last->next;
+    }
+    if (last)
+    {
+        processor->prev = last;
+        last->next = processor;
+    }
+    else stream.buffer->processor = processor;
+
+    ma_mutex_unlock(&AUDIO.System.lock);
+}
+
+void DetachAudioStreamProcessor(AudioStream stream, AudioCallback process)
+{
+    ma_mutex_lock(&AUDIO.System.lock);
+
+    rAudioProcessor *processor = stream.buffer->processor;
+
+    while (processor)
+    {
+        rAudioProcessor *next = processor->next;
+        rAudioProcessor *prev = processor->prev;
+
+        if (processor->process == process)
+        {
+            if (stream.buffer->processor == processor) stream.buffer->processor = next;
+            if (prev) prev->next = next;
+            if (next) next->prev = prev;
+
+            RL_FREE(processor);
+        }
+
+        processor = next;
+    }
+
+    ma_mutex_unlock(&AUDIO.System.lock);
+}
+
 //----------------------------------------------------------------------------------
 // Module specific Functions Definition
 //----------------------------------------------------------------------------------
@@ -2235,6 +2297,14 @@ static void OnSendAudioDataToDevice(ma_device *pDevice, void *pFramesOut, const
                         float *framesOut = (float *)pFramesOut + (framesRead*AUDIO.System.device.playback.channels);
                         float *framesIn = tempBuffer;
 
+                        // Apply processors chain if defined
+                        rAudioProcessor *processor = audioBuffer->processor;
+                        while (processor)
+                        {
+                            processor->process(framesIn, framesJustRead);
+                            processor = processor->next;
+                        }
+
                         MixAudioFrames(framesOut, framesIn, framesJustRead, audioBuffer);
 
                         framesToRead -= framesJustRead;

src/raylib.h

@@ -428,10 +428,12 @@ typedef struct Wave {
 // Opaque structs declaration
 // NOTE: Actual structs are defined internally in raudio module
 typedef struct rAudioBuffer rAudioBuffer;
+typedef struct rAudioProcessor rAudioProcessor;
 
 // AudioStream, custom audio stream
 typedef struct AudioStream {
     rAudioBuffer *buffer;       // Pointer to internal data used by the audio system
+    rAudioProcessor *processor; // Pointer to internal data processor, useful for audio effects
 
     unsigned int sampleRate;    // Frequency (samples per second)
     unsigned int sampleSize;    // Bit depth (bits per sample): 8, 16, 32 (24 not supported)
@@ -1543,6 +1545,9 @@ RLAPI void SetAudioStreamPan(AudioStream stream, float pan);          // Set pan
 RLAPI void SetAudioStreamBufferSizeDefault(int size);                 // Default size for new audio streams
 RLAPI void SetAudioStreamCallback(AudioStream stream, AudioCallback callback);  // Audio thread callback to request new data
 
+RLAPI void AttachAudioStreamProcessor(AudioStream stream, AudioCallback processor);
+RLAPI void DetachAudioStreamProcessor(AudioStream stream, AudioCallback processor);
+
 #if defined(__cplusplus)
 }
 #endif