Replace 'magic' 128 number with a define

Author: cwoffenden

site/source/docs/api_reference/wasm_audio_worklets.rst

@@ -45,7 +45,8 @@ processing graph as AudioWorkletNodes.
 
 Once a class type is instantiated on the Web Audio graph and the graph is
 running, a C/C++ function pointer callback will be invoked for each 128
-samples of the processed audio stream that flows through the node.
+samples (``WEBAUDIO_QUANTUM_SIZE``) of the processed audio stream that flows
+through the node.
 
 This callback will be executed on a dedicated separate audio processing
 thread with real-time processing priority. Each Web Audio context will
@@ -158,7 +159,7 @@ which resumes the audio context when the user clicks on the DOM Canvas element t
                         void *userData)
   {
     for(int i = 0; i < numOutputs; ++i)
-      for(int j = 0; j < 128*outputs[i].numberOfChannels; ++j)
+      for(int j = 0; j < WEBAUDIO_QUANTUM_SIZE*outputs[i].numberOfChannels; ++j)
         outputs[i].data[j] = emscripten_random() * 0.2 - 0.1; // Warning: scale down audio volume by factor of 0.2, raw noise can be really loud otherwise
 
     return true; // Keep the graph output going

system/include/emscripten/webaudio.h

@@ -97,17 +97,20 @@ void emscripten_create_wasm_audio_worklet_processor_async(EMSCRIPTEN_WEBAUDIO_T
 
 typedef int EMSCRIPTEN_AUDIO_WORKLET_NODE_T;
 
+// Number of samples processed per channel in the AudioSampleFrame (fixed at 128 in the Web Audio API specification)
+#define WEBAUDIO_QUANTUM_SIZE 128
+
 typedef struct AudioSampleFrame
 {
 	const int numberOfChannels;
-	// An array of length numberOfChannels*128 elements, where data[channelIndex*128+i] locates the data of the i'th sample of channel channelIndex.
+	// An array of length numberOfChannels*128 elements (128 being WEBAUDIO_QUANTUM_SIZE), where data[channelIndex*128+i] locates the data of the i'th sample of channel channelIndex.
 	float *data;
 } AudioSampleFrame;
 
 typedef struct AudioParamFrame
 {
 	// Specifies the length of the input array data (in float elements). This will be guaranteed to either have
-	// a value of 1 or 128, depending on whether the audio parameter changed during this frame.
+	// a value of 1, for a parameter valid for the entire frame, or 128 (the WEBAUDIO_QUANTUM_SIZE), for a parameter that changes during the frame.
 	int length;
 	// An array of length specified in 'length'.
 	float *data;

test/webaudio/audio_worklet_tone_generator.c

@@ -38,12 +38,12 @@ bool ProcessAudio(int numInputs, const AudioSampleFrame *inputs, int numOutputs,
 
   // Produce a sine wave tone of desired frequency to all output channels.
   for(int o = 0; o < numOutputs; ++o)
-    for(int i = 0; i < 128; ++i)
+    for(int i = 0; i < WEBAUDIO_QUANTUM_SIZE; ++i)
     {
       float s = emscripten_math_sin(phase);
       phase += phaseIncrement;
       for(int ch = 0; ch < outputs[o].numberOfChannels; ++ch)
-        outputs[o].data[ch*128 + i] = s * currentVolume;
+        outputs[o].data[ch*WEBAUDIO_QUANTUM_SIZE + i] = s * currentVolume;
     }
 
   // Range reduce to keep precision around zero.

test/webaudio/audioworklet.c

@@ -40,7 +40,7 @@ bool ProcessAudio(int numInputs, const AudioSampleFrame *inputs, int numOutputs,
 
   // Produce noise in all output channels.
   for(int i = 0; i < numOutputs; ++i)
-    for(int j = 0; j < 128*outputs[i].numberOfChannels; ++j)
+    for(int j = 0; j < WEBAUDIO_QUANTUM_SIZE*outputs[i].numberOfChannels; ++j)
       outputs[i].data[j] = (rand() / (float)RAND_MAX * 2.0f - 1.0f) * 0.3f;
 
   // We generated audio and want to keep this processor going. Return false here to shut down.