processing visual rhythm

rhythm.pde

int FRAME_RATE = 30;
int BPM = 80;
float FPB = FRAME_RATE * 60.0 / BPM;
float BPF = BPM / 60.0 / FRAME_RATE;

float beatCount = 0.0;

int nodeSize = 20;

void setup() {
  size(200, 200, P3D);
  
  frameRate(FRAME_RATE);
}

void draw() {
  background(255);
  
  FPB = frameRate * 60.0 / BPM;
  float modulationRate = FPB;
  
  beatCount = (this.beatCount + 1) % modulationRate; // modulate on every four beats
  float x = map(beatCount, 0, modulationRate, 0, (float) Math.PI);
  float y = sin(x);
  nodeSize = Math.round(map(y, 0, 1, 1, 20));
  
  fill(0);
  rect(90, 90, nodeSize, nodeSize);
  
  text(frameRate, 10, 20);
  text(y, 10, 50);
}