let pipes = [];

​

function setup() {

  createCanvas(640, 240);

  ml5.tf.setBackend("cpu");

  for (let i = 0; i < 200; i++) {

    birds[i] = new Bird();

  }

  pipes.push(new Pipe());

}

​

function draw() {

  background(255);

​

  for (let i = pipes.length - 1; i >= 0; i--) {

    pipes[i].update();

    pipes[i].show();

    if (pipes[i].offscreen()) {

      pipes.splice(i, 1);

    }

  }

​

  for (let bird of birds) {

    if (bird.alive) {

      for (let pipe of pipes) {

        if (pipe.collides(bird)) {

          bird.alive = false;

        }

      }

      bird.think(pipes);

      bird.update();

      bird.show();

    }

  }

​

  if (frameCount % 100 == 0) {

    pipes.push(new Pipe());

  }

​

  if (allBirdsDead()) {

    normalizeFitness();

    reproduction();

    resetPipes();

  }

}

​

function allBirdsDead() {

  for (let bird of birds) {

    if (bird.alive) {

      return false;

    }

  }

  return true;

}

​

function reproduction() {

  let nextBirds = [];

  for (let i = 0; i < birds.length; i++) {

    let parentA = weightedSelection();

    let parentB = weightedSelection();

    let child = parentA.crossover(parentB);

    child.mutate(0.01);

    nextBirds[i] = new Bird(child);

  }

  birds = nextBirds;

}

​

// Normalize all fitness values

function normalizeFitness() {

  let sum = 0;

  for (let bird of birds) {

    sum += bird.fitness;

  }

  for (let bird of birds) {

    bird.fitness = bird.fitness / sum;

  }

}

​

function weightedSelection() {

  // Start with the first element

  let index = 0;

  // Pick a starting point

  let start = random(1);

  // At the finish line?

  while (start > 0) {

    // Move a distance according to fitness

    start = start - birds[index].fitness;

    // Next element

    index++;

  }

  // Undo moving to the next element since the finish has been reached

  index--;

  //{!1} Instead of returning the entire Bird object, just the brain is returned

  return birds[index].brain;

}

​

function resetPipes() {

  // Remove all the pipes but the very latest one

  pipes.splice(0, pipes.length - 1);

}

​