Modified examples to play three sine waves, with the amplitude controlled by three momentary switches connected as digital inputs. Need to do some switch debouncing to get rid of some crackling

bela-btn-test.cpp

#include <Bela.h>
#include <stdio.h>
#include <cmath>
#include <digital_gpio_mapping.h>

float gPhase1, gPhase2, gPhase3;
float gInverseSampleRate;

bool setup(BelaContext *context, void *userData)
{
  //these should already be set by default but I'm learning
  gInverseSampleRate = 1.0 / context->audioSampleRate;
  pinMode(context, 0, P9_12, INPUT);
  pinMode(context, 0, P9_14, INPUT);
  pinMode(context, 0, P9_16, INPUT);
  return true;

}

void render(BelaContext *context, void *userData)
{
  int btn1 = digitalRead(context, 0, P9_12);
  int btn2 = digitalRead(context, 0, P9_14);
  int btn3 = digitalRead(context, 0, P9_16);

  for(unsigned int n = 0; n < context->audioFrames; n++){
    float out = 0.4 * sinf(gPhase1) * btn1;
    out += 0.4 * sinf(gPhase2) * btn2;
    out += 0.4 * sinf(gPhase3) * btn3;
    gPhase1 += 2.0 * M_PI * 440.0 * gInverseSampleRate;
    gPhase2 += 2.0 * M_PI * 660.0 * gInverseSampleRate;
    gPhase3 += 2.0 * M_PI * 770.0 * gInverseSampleRate;
    if(gPhase1 > 2.0 * M_PI)
      gPhase1 -= 2.0 * M_PI;
    if(gPhase2 > 2.0 * M_PI)
      gPhase2 -= 2.0 * M_PI;
    if(gPhase3 > 2.0 * M_PI)
      gPhase3 -= 2.0 * M_PI;

    for(unsigned int channel = 0; channel < context->audioOutChannels; channel++) {
      audioWrite(context, n, channel, out);
    }
  }
}

void cleanup(BelaContext *context, void *userData)
{
  printf("cleaning up\n");
}