var yPos = [];

var sizeX = [];

var sizeY = [];

var speeds = [];

function setup() {

  createCanvas(400, 400);

  var count = 0;

  while (count < 1000) {

    append(xPos, random(400));

    append(yPos, random(400));

    append(speeds, random(0.5, 2));

    append(sizeX, random(3, 7));

    append(sizeY, random(3, 7));

    count++;

  }

  noStroke();

}

​

function draw() {

  background(220);

  var i = 0;

  while (i < xPos.length) {

    fill(255, 255, 255);

    ellipse(xPos[i], yPos[i], sizeX[i], sizeY[i]);

    yPos[i] = yPos[i] + speeds;

    xPos[i] = xPos[i] + random(-1, 1);

    if (yPos[i] > 400) {

      yPos[i] = 0;

    }

    i++;

  }

}

​