const STABILITY_OFFSET = 0.1;

​

const INITIAL_POPULATION_RANGE = [200, 500];

const BIRTH_RATE_RANGE = [1.5, 5];

const DEATH_RATE_RANGE = [0.5, 3];

​

const MAX_POPULATION = 3000;

const MIN_POPULATION = 2;

​

const GRID_SIZE = 4;

const GRID_WIDTH = 800;

​

const TEXT_SIZE = 24;

​

const GROWING_FILL = [100, 150, 200];

const MAX_POPULATION_FILL = [50, 250, 50];

const EXTINCT_FILL = [255, 0, 0];

const POPULATION_FILL = [255];

​

const regions = [];

let mode = 1; // 0 = growth, 1 = random, 2 = stability

​

class Region {

  constructor(x, y, population, fertilityRate, deathRate) {

    this.x = x;

    this.y = y;

    this.population = population;

    this.fertilityRate = fertilityRate;

    this.deathRate = deathRate;

  }

​

  grow() {

    const growthFactor =

      this.population > 2 ? this.fertilityRate - this.deathRate : 0;

    this.population += growthFactor;

    this.population = constrain(

      this.population,

      MIN_POPULATION,

      MAX_POPULATION

    );

  }

​

  display() {

    if (this.population <= MIN_POPULATION) {

      fill(...EXTINCT_FILL);

      textSize(TEXT_SIZE);

      text("extinct", this.x - 50, this.y - 10);

    } else {

      if (this.population === MAX_POPULATION) fill(...MAX_POPULATION_FILL);

      else fill(...GROWING_FILL);

      ellipse(this.x, this.y, this.population / 10);

      fill(...POPULATION_FILL);

      textSize(TEXT_SIZE / 2);

      text(int(this.population), this.x - 10, this.y);

    }

  }

​

  randomizeRates() {

    this.fertilityRate = random(...BIRTH_RATE_RANGE);

    this.deathRate = random(...DEATH_RATE_RANGE);

  }

​

  stabilize() {

    this.fertilityRate = lerp(

      this.fertilityRate,

      REPLACEMENT_RATE + random(-STABILITY_OFFSET, STABILITY_OFFSET),

      0.05

    ); // Gradual shift towards replacement rate

    this.deathRate = lerp(

      this.deathRate,

      REPLACEMENT_RATE + random(-STABILITY_OFFSET, STABILITY_OFFSET),

      0.05

    ); // Shift death rate to balance fertility

  }

}

​

function setup() {

  createCanvas(GRID_WIDTH, GRID_WIDTH, SVG);

  let spacing = GRID_WIDTH / GRID_SIZE;

​

  for (let i = 0; i < GRID_SIZE; i++) {

    for (let j = 0; j < GRID_SIZE; j++) {

      let x = spacing * i + spacing / 2;

      let y = spacing * j + spacing / 2;

      let population = random(...INITIAL_POPULATION_RANGE);

      let fertilityRate = random(...BIRTH_RATE_RANGE);

      let deathRate = random(...DEATH_RATE_RANGE);

      regions.push(new Region(x, y, population, fertilityRate, deathRate));

    }

  }

}

​

function draw() {

  background(255);

  if (mode === 0) growthMode();

  if (mode === 1) randomMode();

  if (mode === 2) stabilityMode();

}

​

function keyPressed() {

  if (key === "1") mode = 0;

  if (key === "2") mode = 1;

  if (key === "3") mode = 2;

​

  // save svg

  if (key === "s") save();

}

​

function growthMode() {

  for (let region of regions) {

    region.grow();

    region.display();

  }

}

​

function randomMode() {

  for (let region of regions) {

    region.randomizeRates();

    region.grow();

    region.display();

  }

}

​

function stabilityMode() {

  for (let region of regions) {

    region.stabilize();

    region.grow();

    region.display();

  }

}

​