gistfile1.pde

void setup() {
  size(500, 500);
}

void draw() {
  background(255);
  
  float period = 50;
  float amplitude = 200;
  
  float x = amplitude * cos(TWO_PI * frameCount / period);
  
  translate(width/2, height/2);
  line(0, 0, x, 0);
  ellipse(x, 0, 20, 20);
}