Cuadrado Que Gira

float r = 0;
float backR;
float backG;
float backB;

void setup() {
  size(400,400);
  backR = random(0,100);
  backG = random(0,100);
  backB = random(0,100);

  background(random(2),random(2),random(2));
  rectMode(CENTER);

  noStroke();
  smooth();
}

void draw() {
  fill(backR, backG, 50, 50);

  rect(width/2, height/2, width, height);

  fill(255);
  translate(mouseX, mouseY);
  rotate(r);
  rect(0, 0, 100, 100);

  r = r + 1.5;
}