float x, i, j, n;
float y = 0;

void setup() 
{
  size(400,400);
  noStroke();
  frameRate(5);
  x = random(width);
}

void draw() 
{
  background(50);
  i = random(50)/10;
  j = random(20) - i;
  
  if (y > height) {
    y = 0;
  } 
  y = y + i;
  translate(j, y);
  ellipse(x, y, 2, 2);
}