Run Length Encoding file format pattern parser for Conway's Game of Life

rle.js

module.exports = function decode(string) {
  var cells = []
  var ignore = false
  var step = 1
  var x = 0
  var y = 0
  var match, number
  for (var i = 0; i < string.length; i++) {
    if (ignore) {
      if (string[i] === "\n") {
        ignore = false
      }
      continue
    }
    switch (string[i]) {
      case "#":
      case "x":
      case "!":
        ignore = true
        continue
      case "$":
        x = 0
        y += step
        continue
      case "b":
        x += step
        step = 1
        continue
      case "o":
        for (var j = 0; j < step; j++) {
          cells.push(x++, y)
        }
        step = 1
        continue
    }
    match = string.slice(i).match(/[0-9]+/)
    if (match && !match.index) {
      number = match[0]
      step = parseInt(number)
      i += number.length - 1
    }
  }
  return cells
}

Thanks for the code. One thing.. on line 21

case "$": x = 0; y++

should be y += step to accommodate multiple empty lines

late to the punch but you're absolutely right. Good catch

Found this code because I was trying to write my own decoder. But I'm not sure what you're supposed to do with the outputs of this function.

When I try the following pattern with it, I just get a long array of array of numbers.

#C this is a fake comment
x = 187, y = 187, rule = B3/S23
179bobo$179b2o$180bo$$$o$b2o$2o14bo25bo$14bobo26b2o128bo$15b2o25b2o
128bo$172b3o$$10bo26bo$8bobo27b2o128bo$9b2o26b2o128bo10bo$167b3o7bo$
177b3o$15bo$13bobo28bo$14b2o29b2o$44b2o$$$129bo$129bobo$129b2o$$$130bo
$128b2o$129b2o$40bo$41b2o$40b2o$52bo$53bo$51b3o17bobo$72b2o98bobo$72bo
99b2o$54bo118bo$55bo69bo$53b3o68bo$124b3o50bobo$177b2o$166bobo9bo$166b
2o$122bobo42bo$122b2o$123bo$$$120bobo$71bobo46b2o$72b2o47bo$72bo58bo$
130bo$130b3o$$72bo63bo$66bo3bobo61b2o$61bo5b2o2b2o62b2o$62bo3b2o$60b3o
$$108bo$108bobo3bo$108b2o2b2o$113b2o$$107bobo$107b2o$108bo$$83bo$84bo
2bo$44bo2bobo32b3o3b2o34bobo$42bobo3b2o37b2o35b2o$43b2o3bo76bo$$66bo
26bo18bo$67bo25bobo15bo$65b3o25b2o16b3o$$$77bobo34bo$78b2o32b2o$78bo
34b2o$133bo$77bo55bobo$78bo2bo51b2o$76b3o3b2o$81b2o$$$99bo$98bo$98b3o$
$$$$$$69b2o$70b2o$69bo$$$120b3o$120bo$121bo16b2o$137b2o$73b2o64bo$72bo
bo$74bo$81b2o$33bo48b2o33bo10b2o$33b2o46bo34b2o9b2o$32bobo81bobo10bo$$
109b2o$52b3o54bobo$54bo54bo$53bo$$51bo106b2o$51b2o105bobo$50bobo105bo$
$$$$98bo$97b2o$97bobo26b2o$126bobo$126bo$75b2o$74bobo$76bo$19bo$19b2o$
8bo9bobo54b2o$8b2o66b2o$7bobo65bo$$$13bo$13b2o$12bobo$$$$$$$$$$$$$$$$$
141b2o$140b2o29b2o$142bo28bobo$171bo$7b3o$9bo7b3o$8bo10bo128b2o26b2o$
18bo128b2o27bobo$149bo26bo$$12b3o$14bo128b2o25b2o$13bo128b2o26bobo$
144bo25bo14b2o$184b2o$186bo$$$6bo$6b2o$5bobo!

This is the RLE for https://copy.sh/life/?pattern=112p51_synth.

The results I'm seeing are like this:

hi Charles -- what you're looking at is a flattened list of (x, y) pairs of living cells in the resulting pattern. So if you're looking to convert that to a 2d array you'd do something like this (untested):

function convertLifeCellsToGrid(cells) {
  let width = 0
  let height = 0

  for (let i = 0; i < cells.length; i += 2) {
    let x = cells[i]
    let y = cells[i + 1]
    width = Math.max(x + 1, width)
    height = Math.max(y + 1, height)
  }

  const grid = new Array(height)
    .fill()
    .map(_ => new Uint8ClampedArray(width))

  for (let i = 0; i < cells.length; i += 2) {
    let x = cells[i]
    let y = cells[i + 1]
    grid[y][x] = 1
  }

  return grid
}

I have an example implementation of life up that uses the original cell list if you're interested.