make it work (1s, 440Hz tone)

coreaudio_example_main.cc

@@ -1 +1,58 @@
-int main() { return 0; }
+#include "coreaudio_example.h"
+
+static double gtheta = 0;
+
+OSStatus tone(void *inRef, AudioUnitRenderActionFlags *ioActionFlags, const AudioTimeStamp *inTimeStamp, UInt32 inBusNumber, UInt32 inNumberFrames, AudioBufferList *ioData) {
+    // Fixed amplitude is good enough for our purposes
+    const double amplitude = 0.25;
+
+    // Get the tone parameters out of the static var
+    // could be stored in inRef
+    double theta = gtheta;
+    double theta_increment = 2.0 * M_PI * 440 / 44100;
+
+    // This is a mono tone generator so we only need the first buffer
+    const int channel = 0;
+    Float32 *buffer = (Float32 *)ioData->mBuffers[channel].mData;
+
+    // Generate the samples
+    for (UInt32 frame = 0; frame < inNumberFrames; frame++) 
+    {
+        buffer[frame] = sin(theta) * amplitude;
+
+        theta += theta_increment;
+        if (theta > 2.0 * M_PI)
+        {
+            theta -= 2.0 * M_PI;
+        }
+    }
+
+    printf("%f\n", theta);
+    gtheta = theta;
+
+    return noErr;
+}
+
+int main() {
+    coreaudio_example::init();
+
+    AURenderCallbackStruct callback;
+    callback.inputProc = tone;
+    callback.inputProcRefCon = nullptr; // could pass a struct to store state like theta
+
+    bool ok = coreaudio_example::open_audio(coreaudio_example::FMT_FLOAT, 44100, 1, &callback);
+    if (!ok) {
+        coreaudio_example::cleanup();
+        fprintf(stderr, "failed to open\n");
+        return 1;
+    }
+
+    coreaudio_example::set_volume(100);
+
+    // sleep 1s, rendering via callback happens in another thread
+    usleep(1000000);
+
+    coreaudio_example::close_audio();
+    coreaudio_example::cleanup();
+    return 0;
+}