let yPositions = [];

let speed = [];

​

function setup() {

  createCanvas(400, 400);

  for (let i = 0; i < 100; i++) {

    append(xPositions, random(-400, 400));

    append(yPositions, random(-200, 0));

    append(speed, random(1, 2));

  }

}

​

function draw() {

  background(0, 0, 50, 50);

  stroke(0, 0, 220);

  fill(0, 0, 220);

  rect(0, 350, 400, 50);

  stroke(255, 255, 255);

  fill(255, 255, 255);

  for (let i = 0; i < xPositions.length; i++) {

    ellipse(xPositions[i], yPositions[i], 1, 1);

    yPositions[i] = yPositions[i] + speed[i];

    xPositions[i] = xPositions[i] + speed[i];

    if (yPositions[i] > 350) {

      xPositions[i] = random(-400, 400);

      yPositions[i] = random(-200, 0);

    }

    if (xPositions[i] > 400) {

      xPositions[i] = random(-400, 400);

      yPositions[i] = random(-200, 0);

    }

  }

}

​