void setup() {
  size(400, 400);
  background(255);
  rectMode(CENTER);
}

void draw() {
  // fading effect
  fill(255, 32);
  noStroke();
  rect(width/2, height/2, width, height);
 
  float x = random(width);
  float y = random(height);
  float r = random(TWO_PI);
  
  translate(x, y);
  rotate(r);
  stroke(0);
  fill(150);
  rect(0, 0, 50, 50);
}