Conway's Game of Life in Nim

life.nim

# Conway's Game of Life
#
# Initialises the canvas randomly
#
# nimble install sdl2
# nim c -r life.nim

from random import randomize, rand

import sdl2

const SCREEN_WIDTH  = 256
const SCREEN_HEIGHT = 240

func next_step(canvas: array[SCREEN_HEIGHT, array[SCREEN_WIDTH, bool]], x: int, y: int): bool =
  var on = 0

  # Vertical neighbors
  if y > 0 and canvas[y - 1][x]:
    on += 1;
  if (y < ScreenHeight - 1) and canvas[y + 1][x]:
    on += 1;

  # Horizontal neighbors
  if x > 0 and canvas[y][x - 1]:
    on += 1;
  if (x < ScreenWidth - 1) and canvas[y][x + 1]:
    on += 1;

  # Diagonally adjacent neighbors
  if x > 0 and y > 0 and canvas[y - 1][x - 1]:
    on += 1;
  if (x < ScreenWidth - 1) and (y < ScreenHeight - 1) and canvas[y + 1][x + 1]:
    on += 1;
  if x > 0 and (y < ScreenHeight - 1) and canvas[y + 1][x - 1]:
    on += 1;
  if (x < ScreenWidth - 1) and y > 0 and canvas[y - 1][x + 1]:
    on += 1;

  if canvas[y][x]:
    if on == 1:
      return false
    elif on == 2 or on == 3:
      return true
    elif on == 4:
      return false
  elif on == 3:
    return true

  return false


proc main =
  randomize()

  var current_canvas: array[SCREEN_HEIGHT, array[SCREEN_WIDTH, bool]]

  for y in 0 .. SCREEN_HEIGHT - 1:
    for x in 0 .. SCREEN_WIDTH - 1:
      current_canvas[y][x] = rand(1.0) < 0.5

  if not sdl2.init(INIT_VIDEO):
    echo "sdl2 init failed"
    return

  defer: sdl2.quit()

  let window = sdl2.createWindow(
    "Game of Life",
    100,
    100,
    SCREEN_WIDTH * 2,
    SCREEN_HEIGHT * 2,
    sdl2.SDL_WINDOW_SHOWN
  )
  defer: window.destroy()

  let surface = sdl2.getSurface(window)

  var quit = false
  var next_canvas: array[SCREEN_HEIGHT, array[SCREEN_WIDTH, bool]]
  var event = sdl2.defaultEvent

  while not quit:
    while sdl2.pollEvent(event):
      if event.kind == sdl2.QuitEvent:
        quit = true

    for y in 0 .. SCREEN_HEIGHT - 1:
      for x in 0 .. SCREEN_WIDTH - 1:
        let onoff = next_step(current_canvas, x, y)
        next_canvas[y][x] = onoff

        let rgb: uint32 = if onoff: 0x00 else: 0xff
        let color = (rgb shl 24) or (rgb shl 16) or (rgb shl 8) or rgb
        var rect = sdl2.rect(cint(x) * 2, cint(y) * 2, 2, 2)
        sdl2.fillRect(surface, rect.addr, color)

    current_canvas = next_canvas

    if not sdl2.updateSurface(window):
      echo "Failed to update surface"
      break

    sdl2.delay(100)

main()