​

function setup() {

  createCanvas(400, 400);

}

​

function draw() {

  background(220);

  rect(150, 150, 100, 100);

​

  if (mouseX > 150 && mouseX < 250 && mouseY > 150 && mouseY < 250 && buttonDown == false) {

    fill(120);

  } else {

    fill(255);

  }

}

​

function mousePressed() {

  if (mouseX > 150 && mouseX < 250 && mouseY > 150 && mouseY < 250 && buttonDown == false) {

    fill(0);

    buttonDown = true;

  } else if (mouseX > 150 && mouseX < 250 && mouseY > 150 && mouseY < 250 && buttonDown == true) {

    buttonDown = false;

    fill(255);

  }

}

​