let vecLocation = [];

let vecVelocity = [];

let diameter = [];

let col = [];

function setup() {

  createCanvas(windowWidth, windowHeight);

  frameRate(60);

  for(let i = 0; i < num; i++){

    vecLocation[i] = createVector(width / 2, height / 2);

    vecVelocity[i] = createVector(random(-10, 10), random(-10, 10));

    diameter[i] = random(5, 40);

    col[i] = color(random(255), random(255), random(255), 200);

  }

}

​

function draw() {

  background(0);

  noStroke();  

  for(let i = 0; i < num; i++){

    fill(col[i]);

    vecLocation[i].add(vecVelocity[i]);

    circle(vecLocation[i].x, vecLocation[i].y, diameter[i]);

    if (vecLocation[i].x < 0 || vecLocation[i].x > width) {

      vecVelocity[i].x = vecVelocity[i].x * -1;

    }

    if (vecLocation[i].y < 0 || vecLocation[i].y > height) {

      vecVelocity[i].y = vecVelocity[i].y * -1;

    }

  }

}