let x2, y2; // Circle moving right

let x3, y3; // Circle moving up

let x4, y4; // Circle moving down

​

function setup() {

  createCanvas(400, 400);

​

  // all ball start center of the canvas

  x1 = width / 2;

  y1 = height / 2;

  x2 = width / 2;

  y2 = height / 2;

  x3 = width / 2;

  y3 = height / 2;

  x4 = width / 2;

  y4 = height / 2;

}

​

function draw() {

  background(220);

​

  // Circle moving left

  fill(255);

  ellipse(x1, y1, 20, 20);

  x1 -= 1; // Move left

​

  // Circle moving right

  fill(255);

  ellipse(x2, y2, 20, 20);

  x2 += 1; // Move right

​

  // Circle moving up

  fill(255);

  ellipse(x3, y3, 20, 20);

  y3 -= 1; // Move up

​

  // Circle moving down

  fill(255);

  ellipse(x4, y4, 20, 20);

  y4 += 1; // Move down

}

​