Extras/userdata/render.cpp

Passing parameters using the *userData argument

This sketch demonstrates how to pass command line arguments using the *userData argument inside the setup() function.

In main.cpp we first parse a command line argument -f and allocate its value to the variable frequency. We then pass the address of this variable when we call Bela_initAudio(). The variable can now be accessed from the setup() and render() functions inside render.cpp.

/*
 ____  _____ _        _
| __ )| ____| |      / \
|  _ \|  _| | |     / _ \
| |_) | |___| |___ / ___ \
|____/|_____|_____/_/   \_\
http://bela.io
*/
 
#include <Bela.h>
#include <cmath>
 
float gFrequency = 440.0;
float gPhase;
float gInverseSampleRate;
 
bool setup(BelaContext *context, void *userData)
{
        /*
         *  Retrieve the parameter passed in from the Bela_initAudio() call in main.cpp
         */
        if(userData != 0)
                gFrequency = *(float *)userData;
 
        gInverseSampleRate = 1.0 / context->audioSampleRate;
        gPhase = 0.0;
 
        return true;
}
 
void render(BelaContext *context, void *userData)
{
        for(unsigned int n = 0; n < context->audioFrames; n++) {
                float out = 0.8f * sinf(gPhase);
                gPhase += 2.0 * M_PI * gFrequency * gInverseSampleRate;
                if(gPhase > 2.0 * M_PI)
                        gPhase -= 2.0 * M_PI;
 
                for(unsigned int channel = 0; channel < context->audioOutChannels; channel++) {
                        audioWrite(context, n, channel, out);
                }
        }
}
 
void cleanup(BelaContext *context, void *userData)
{
 
}