float angle=0;
void setup() {
size(300, 300);
noStroke();
smooth();
}

void drawCircle(float a) {
  fill(0);
  ellipse(a,150, 60, 60);
  fill(255);
  ellipse(150,a,40,40);
}

void draw() {
  background(144);
  float a = 50+cos(angle)*30;
  drawCircle(a);
  angle += 0.03;
}