Star[] stars = new Star[400];

void setup() {
  size(800,800);
  smooth();
  stroke(255);
  strokeWeight(5);
  for (int i = 0; i < stars.length; i++) {
    stars[i] = new Star();
  }
}

void draw() {
  background(0);
  translate(width/2, height/2);
  for (int i = 0; i < stars.length; i++) {
    stars[i].update();
    stars[i].show();
  }
}


class Star {
    float x;
    float y;
    float z;

    float pz;

  Star() {
    x = random(-width, width);
    y = random(-height, height);
    z = random(0, 2000);
    pz = z;
  }

  void update() {
    pz = z + 100;
    z = z - 20;
    if (z<1) {
      z = 2000;
      y = random(-height, height);
      x = random(-width, width);
      pz = z;
    }
  }

  void show() {
    fill(255);
    noStroke();

    float sx = map(x/z, 0, 1, 0, width);
    float sy = map(y/z, 0, 1, 0, width);

    float r = map(z-1000, 0, width, 16, 0);
    ellipse(sx, sy, r, r);

    float px = map(x/pz, 0, 1, 0, width);
    float py = map(y/pz, 0, 1, 0, height);

    stroke(255);
    line(px, py, sx, sy);
  }
}