​

function setup() {

  createCanvas(400, 400);

}

​

function draw() {

  background(220);

​

  if (mode == 0) {

    screen1();

  } else if (mode == 1) {

    screen2();

  } else if (mode == 2) {

    screen3();

  }

}

​

//Useful to have multiple elements on one screen

function screen1() {

  ellipse(width / 2, height / 2, 300, 300);

}

​

function screen2() {

  rect(50, 50, 300, 300);

}

​

function screen3() {

  line(0, 0, width, height);

  line(0, width, width, 0);

}

​

​

//Method 1: More flexible, any order

function mousePressed() {

  if (mode == 0) {

    mode = 1;

  } else if (mode == 1) {

    mode = 2;

  } else if (mode == 2) {

    mode = 0;

  }

}

​

//Method 2: Can only go in order

// function mousePressed(){

//   mode=mode+1;

//   if (mode==3) {

//     mode=0;

//   }

//   print(mode);

// }