current = [],

    previous = [],

    curImg = [];

    prevImg = [];

    damping = 0.9;

      let img;

​

function preload(){

  img = loadImage('img.jpg');

}

​

  function mouseDragged() {

    current[mouseX][mouseY] = 255

  }

​

​

  function setup() {

    pixelDensity(1)

    createCanvas(400, 400)

    cols = width

    rows = height

    for (let i = 0; i < cols; i++) {

      current[i] = []

      previous[i] = []

​

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

        current[i][j] = 0

        previous[i][j] = 0

​

        let index = i+ j*cols;

        for(let k = index+0; k < index+4; k++){

          curImg[k]= img.pixels[index + k];

          prevImg[k] = img.pixels[index + k];

        }

      }

    }

    previous[100][100] = 255

​

  }

​

  function draw() {

    background(0)

    // loadPixels();

    img.loadPixels();

    for (let i = 1; i < cols - 1; i++) {

      for (let j = 1; j < rows - 1; j++) {

        current[i][j] =

          (previous[i - 1][j] + previous[i + 1][j] +

            previous[i][j - 1] + previous[i][j + 1] +

            previous[i - 1][j - 1] + previous[i - 1][j + 1] +

            previous[i + 1][j - 1] + previous[i + 1][j + 1]

          ) / 4 - current[i][j];

        current[i][j] = current[i][j] * damping

        let index = (i + j * cols) * 4;

        pixels[index + 0] = current[i][j] * 255

        pixels[index + 1] = current[i][j] * 255

        pixels[index + 2] = current[i][j] * 255

        pixels[index + 3] = 255

        if(current[i][j] > 0){

          let index = i+ j*cols;

          for(let k = index+0; k < index+3; k++){

            curImg[k] =

          (prevImg[k-4] + prevImg[k+4] +

            prevImg[k-4*cols] + prevImg[k+4*cols] +

            prevImg[k-4*cols - 4] + prevImg[k-4*cols + 4] +

            prevImg[k+4*cols-4] + prevImg[k+4*cols+4]

          ) / 4 - curImg[k];

       curImg[k] = curImg[k] * damping

          }

          curImg[index+3] = 255;

          prevImg[index+3] = 255;

          img.pixels[index+0] = curImg[index+0];

          img.pixels[index+1] = curImg[index+1];

          img.pixels[index+2] = curImg[index+2];

          img.pixels[index+3] = curImg[index+3];

        }

      }

    }

    // updatePixels()

    img.updatePixels();

    image(img,0,0)

    //swap buffers

    let temp = previous

    previous = current

    current = temp

    let tempImg = prevImg

    prevImg = curImg

    curImg = tempImg

  }