var r = 350;

var on = true;

​

function setup() {

  createCanvas(600, 400);

}

​

function mousePressed() {

  if (mouseX < r && mouseX > l && mouseY > 150 && mouseY < 250) {

    on = !on;

  }

}

​

function draw() {

  if (on) {

    background(0, 180, 220);

  } else {

    background(0);

  }

  rectMode(CENTER);

  fill(0);

  stroke(255);

  if (mouseX < r && mouseX > l && mouseY > 150 && mouseY < 250) {

    fill(255);

  }

  rect(300, 200, 100, 100);

​

}