import java.util.Random;
Random rnd = new Random();

void setup() {
  size(400,400);
  smooth();
  drawstuff();
}

void draw() {
  // leaving this blank, but it has to exist for mousePressed()
  // to get noticed
}

void drawstuff() {
  background(75,150,255);
  for(int i=0; i < 400; i++) {
    int size=(int)random(25,100);
    int x = (int)(rnd.nextGaussian() * 50) + 200;
    int y = (int)(rnd.nextGaussian() * 50) + 200;
    stroke(0);
    strokeWeight(0.25);
    noFill();
    ellipse(x, y, size, size);
  }
  for(int i=0; i < 300; i++) {
    int size=(int)random(25,100);
    int x = (int)(rnd.nextGaussian() * 50) + 200;
    int y = (int)(rnd.nextGaussian() * 50) + 200;
    noStroke();
    fill(255,30);
    ellipse(x, y, size, size);
  }
}

void mousePressed() {
  drawstuff();
}