Breath

const w = 640;

const brushRadius = 25;

let grid = new Uint8Array(w * w);

let zoom;

​

function setup() {

  const m = min(windowWidth, windowHeight);

  createCanvas(m, m);

  zoom = w / m;

  pixelDensity(zoom);

  loadPixels();

  grid = grid.map((v) => (v = floor(random(256))));

}

​

function draw() {

  const newGrid = new Uint8Array(grid);

  for (let y = 1; y < w - 1; y++) {

    for (let x = 1; x < w - 1; x++) {

      const i = x + y * w;

      const oldValue = grid[i];

      const sum = oldValue

        + grid[i - w] * 2

        + grid[i - 1]

        + grid[i + 1]

        + grid[i + w]

        + grid[i - 1 - w] 

        + grid[i + 1 - w] 

        + grid[i - 1 + w] 

        + grid[i + 1 + w] ;

      const average = floor(sum / 10);

      const newValue = (average + 1) & 0xff;

      newGrid[i] = newValue;

      pixels[i * 4 + 3] = newValue > oldValue ? 0 : 255;

    }

  }

  grid = newGrid;

  updatePixels();

}

​

function mouseDragged() {

  for (let dy = -brushRadius; dy <= brushRadius; dy++) {

    for (let dx = -brushRadius; dx <= brushRadius; dx++) {

      if (dx ** 2 + dy ** 2 > brushRadius ** 2) continue;

      const x = floor(mouseX * zoom + dx);

      const y = floor(mouseY * zoom + dy);

      if (0 <= x && x < w && 0 <= y && y < w)

        grid[x + y * w] = random(256);

    }

  }

}