fire.js

const firePixelsArray = []
const fireWidth = 100
const fireHeight = 50
const fireColorsPalette = [{"r":7,"g":7,"b":7},{"r":31,"g":7,"b":7},{"r":47,"g":15,"b":7},{"r":71,"g":15,"b":7},{"r":87,"g":23,"b":7},{"r":103,"g":31,"b":7},{"r":119,"g":31,"b":7},{"r":143,"g":39,"b":7},{"r":159,"g":47,"b":7},{"r":175,"g":63,"b":7},{"r":191,"g":71,"b":7},{"r":199,"g":71,"b":7},{"r":223,"g":79,"b":7},{"r":223,"g":87,"b":7},{"r":223,"g":87,"b":7},{"r":215,"g":95,"b":7},{"r":215,"g":95,"b":7},{"r":215,"g":103,"b":15},{"r":207,"g":111,"b":15},{"r":207,"g":119,"b":15},{"r":207,"g":127,"b":15},{"r":207,"g":135,"b":23},{"r":199,"g":135,"b":23},{"r":199,"g":143,"b":23},{"r":199,"g":151,"b":31},{"r":191,"g":159,"b":31},{"r":191,"g":159,"b":31},{"r":191,"g":167,"b":39},{"r":191,"g":167,"b":39},{"r":191,"g":175,"b":47},{"r":183,"g":175,"b":47},{"r":183,"g":183,"b":47},{"r":183,"g":183,"b":55},{"r":207,"g":207,"b":111},{"r":223,"g":223,"b":159},{"r":239,"g":239,"b":199},{"r":255,"g":255,"b":255}]

//função de inicialização
function start() {
  createFireDataStructure()
  createFireSource();
  renderFire();

  setInterval(calculateFirePropagation, 100);
}

function createFireDataStructure() {
  const numberOfPixels = fireWidth * fireHeight

  for(let i=0; i<numberOfPixels; i++) {
    firePixelsArray[i] = 0
  }
}

function calculateFirePropagation() {
  for(let column = 0; column < fireWidth; column++) {
    for(let row = 0; row < fireHeight; row++) {
      const pixelIndex = column + ( fireWidth * row );

      updateFireIntensityPerPixel(pixelIndex)
    }
  }

  renderFire();
}

function updateFireIntensityPerPixel(currentPixelIndex) {
  const belowPixelIndex = currentPixelIndex + fireWidth;

  if(belowPixelIndex >= fireWidth * fireHeight) {
    return;
  }

  const decay = Math.floor(Math.random() * 3);
  const belowPixelFireIntensity = firePixelsArray[belowPixelIndex]
  const newFireIntensity = 
    belowPixelFireIntensity - decay >= 0 ? belowPixelFireIntensity - decay : 0;

  firePixelsArray[currentPixelIndex - decay] = newFireIntensity
}

function renderFire() {
  const debug = false;
  let html = '<table cellpadding=0 cellspacing=0>'

  for(let row = 0; row < fireHeight; row++){
    html += '<tr>'

    for(let column = 0; column < fireWidth; column++){
      const pixelIndex = column + (fireWidth * row);
      const fireIntensity = firePixelsArray[pixelIndex];

      if (debug === true) {
        html += '<td>'
        html += `<div class="pixel-index">${pixelIndex}</div>`
        html += fireIntensity;
        html += '</td>'
      }else {
        const color = fireColorsPalette[fireIntensity]
        const colorString = `${color.r},${color.g},${color.b}`
        html += `<td class="pixel" style="background-color: rgb(${colorString})">`
        html += '</td>'
      }
    }

    html += '</tr>'
  }

  html += '</table>'

  document.querySelector('#fireCanvas').innerHTML = html;
}

function createFireSource() {
  for(let column = 0; column <= fireWidth; column++){
    const overflowPixelIndex = fireWidth * fireHeight;
    const pixelIndex = (overflowPixelIndex - fireWidth) + column;

    firePixelsArray[pixelIndex] = 36;
  }
}

start()