let t = 0; let a = 0; let num = 360/2; 

let x = []; let y = []; let n;

​

let disp = []; 

​

function setup() {

  createCanvas(400, 400);

  angleMode(DEGREES);

  for(let i=0; i<num; i++) {

    if (i < num/4) {

      disp[i] = 3*cos(360*i/(num/4));

    } else {

      disp[i] = 3*cos(0);

    }

  }

}

​

function draw() {

  background(220);

  translate(width/2, height/2);

​

  noFill();

  stroke(255);

  beginShape();

  for (let i=0; i<num; i++) {

    radius[i] = disp[(i+a)%num]; 

    x[i] = (r+radius[i])*cos(map(i, 0, num, 0, 360));

    y[i] = (r+radius[i])*sin(map(i, 0, num, 0, 360));

    vertex(x[i], y[i]);

    // ellipse(x[i], y[i], 3, 3);

  }

  endShape(CLOSE);

  a += 1;

}