let x2; let y2;

let x3; let y3;

let x4; let y4;

​

let a1; let b1;

let a2; let b2;

let a3; let b3;

let a4; let b4;

​

let s; // Speed

let d; // Direction

​

let dia;

​

​

function setup() {

  createCanvas(800, 800);

   x1 = width / 2; y1 = height / 2;

   x2 = width / 2; y2 = height / 2;

   x3 = width / 2; y3 = height / 2;

   x4 = width / 2; y4 = height / 2;

   a1 = width*0; b1 = height*0;

   a2 = width;   b2 = height*0;

   a3 = width*0; b3 = height;

   a4 = width;   b4 = height;

  dia = 80;

   s = .5; 

   d = 1; 

   // d = (+) = right/ bottom; d = (-) = left/ top

}

​

function draw() {

  background(10);

  noStroke();

  circle(x1, y1, dia);

  circle(x2, y2, dia);

  circle(x3, y3, dia);

​

  circle(x4, y4, dia);

  if(millis() > 1000){

  x1 = x1 + s*d;

  x2 = x2 + s*-d;

  y3 = y3 + s*d;

  y4 = y4 + s*-d;

 }

  circle(a1, b1, dia);

  circle(a2, b2, dia);

  circle(a3, b3, dia);

​

  circle(a4, b4, dia);

   if(x1 > width*0.6){ 

  a1 = a1 + s*d; 

  b1 = b1 + s*d; 

  a2 = a2 + s*-d; 

  b2 = b2 + s*d; 

  a3 = a3 + s*d; 

  b3 = b3 + s*-d; 

  a4 = a4 + s*-d; 

  b4 = b4 + s*-d; 

   }

}