// The Coding Train / Daniel Shiffman

// https://thecodingtrain.com/challenges/13-reaction-diffusion

// https://youtu.be/BV9ny785UNc

// https://nebula.tv/videos/the-coding-train-coding-challenge-13-reaction-diffusion-algorithm-in-p5js

​

// Code from Challenge: https://editor.p5js.org/codingtrain/sketches/govdEW5aE

// Written entirely based on

// http://www.karlsims.com/rd.html

​

// Also, for reference

// http://hg.postspectacular.com/toxiclibs/src/44d9932dbc9f9c69a170643e2d459f449562b750/src.sim/toxi/sim/grayscott/GrayScott.java?at=default

​

var grid;

var next;

​

​

var dA = 1;

var dB = 1.4;

var feed = 0.055;

var k = 0.075;

var t = 1;

​

function setup() {

  createCanvas(400, 400);

  pixelDensity(1);

  cols = ["#03045e","#023e8a","#0077b6","#0096c7","#00b4d8","#48cae4","#90e0ef","#ade8f4","#caf0f8"];

  grid = [];

  next = [];

  var a = color(0);

  var b = color(0);

  var c = color(0);

  for (var x = 0; x < width; x++) {

    grid[x] = [];

    next[x] = [];

    for (var y = 0; y < height; y++) {

      grid[x][y] = {

        a: 1,

        // b: 0

        b: noise(x / 100, y / 100)

      };

      next[x][y] = {

        a: 1,

        b: noise(x / 10, y / 10)

      };

    }

  }

​

  // for (var i = 100; i < 110; i++) {

  //   for (var j = 100; j < 110; j++) {

  //     grid[i][j].b = 1;

  //   }

  // }

  // next = grid;

}

​

function draw() {

  background(51);

  loadPixels();

  for (var x = 1; x < width - 1; x++) {

    for (var y = 1; y < height - 1; y++) {

      var a = grid[x][y].a;

      var b = grid[x][y].b;

      next[x][y].a = a +

        (dA * laplaceA(x, y)) -

        (a * b * b) +

        (feed * (1 - a)) * t;

      next[x][y].b = b +

        (dB * laplaceB(x, y)) +

        (a * b * b) -

        ((k + feed) * b) * t;

​

      next[x][y].a = constrain(next[x][y].a, 0, 1);

      next[x][y].b = constrain(next[x][y].b, 0, 1);

      var col = color(cols[floor(map(next[x][y].b, 0, 1, 0, cols.length - 1))]);

      var pix = (x + y * width) * 4;

      a = red(col);

      b = green(col);

      c = blue(col);

      c = constrain(c, 0, 255);

      pixels[pix + 0] = a;

      pixels[pix + 1] = b;

      pixels[pix + 2] = c;

      pixels[pix + 3] = 255;

    }

  }

updatePixels();

​

//   loadPixels();

//   for (var x = 0; x < width; x++) {

//     for (var y = 0; y < height; y++) {

//       var pix = (x + y * width) * 4;

//       var a = next[x][y].a;

//       var b = next[x][y].b;

//       var c = floor((a - b) * 255);

//       c = constrain(c, 0, 255);

//       pixels[pix + 0] = a * 255;

//       pixels[pix + 1] = c;

//       pixels[pix + 2] = b * 255;

//       pixels[pix + 3] = 255;

//     }

//   }

//   updatePixels();

​

  swap();

​

​

}

​

​

function laplaceA(x, y) {

  var sumA = 0;

  sumA += grid[x][y].a * -1;

  sumA += grid[x - 1][y].a * 0.2;

  sumA += grid[x + 1][y].a * 0.2;

  sumA += grid[x][y + 1].a * 0.2;

  sumA += grid[x][y - 1].a * 0.2;

  sumA += grid[x - 1][y - 1].a * 0.05;

  sumA += grid[x + 1][y - 1].a * 0.05;

  sumA += grid[x + 1][y + 1].a * 0.05;

  sumA += grid[x - 1][y + 1].a * 0.05;

  // sumA = sumA * sumA;

  return sumA;

}

​

function laplaceB(x, y) {

  var sumB = 0;

  sumB += grid[x][y].b * -1;

  sumB += grid[x - 1][y].b * 0.2;

  sumB += grid[x + 1][y].b * 0.2;

  sumB += grid[x][y + 1].b * 0.2;

  sumB += grid[x][y - 1].b * 0.2;

  sumB += grid[x - 1][y - 1].b * 0.05;

  sumB += grid[x + 1][y - 1].b * 0.05;

  sumB += grid[x + 1][y + 1].b * 0.05;

  sumB += grid[x - 1][y + 1].b * 0.05;

  // sumB = sumB * sumB;

  return sumB;

}

​

​

​

function swap() {

  var temp = grid;

  grid = next;

  next = temp;

}