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.

/*
 ____  _____ _        _    
| __ )| ____| |      / \   
|  _ \|  _| | |     / _ \  
| |_) | |___| |___ / ___ \ 
|____/|_____|_____/_/   \_\

The platform for ultra-low latency audio and sensor processing

http://bela.io

A project of the Augmented Instruments Laboratory within the
Centre for Digital Music at Queen Mary University of London.
http://www.eecs.qmul.ac.uk/~andrewm

(c) 2016 Augmented Instruments Laboratory: Andrew McPherson,
        Astrid Bin, Liam Donovan, Christian Heinrichs, Robert Jack,
        Giulio Moro, Laurel Pardue, Victor Zappi. All rights reserved.

The Bela software is distributed under the GNU Lesser General Public License
(LGPL 3.0), available here: https://www.gnu.org/licenses/lgpl-3.0.txt
*/

#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++) {
                        // Two equivalent ways to write this code

                        // The long way, using the buffers directly:
                        // context->audioOut[n * context->audioOutChannels + channel] = out;

                        // Or using the macros:
                        audioWrite(context, n, channel, out);
                }
        }
}

void cleanup(BelaContext *context, void *userData)
{

}