Simple dithering for PICO-8

dithering.p8

pico-8 cartridge // http://www.pico-8.com
version 18
__lua__

-- simple 1-bit dithering by Andrew @retran Vasilyev

function _draw()
  cls()
  for x = 0, 128, 1 do
    for y = 0, 128, 1 do
      local intensity = x / 128
      local color = flr(y / 8) * dither(x, y, intensity)
      pset(x, y, color)
    end
  end
end

function dither(xc, yc, value)
  local ox = xc % 3
  local oy = yc % 3
  if value > 0.9 then
    return 1
  elseif value > 0.75 then
    if (ox == 1 and oy == 1) then
      return 0
    end
    return 1    
  elseif value > 0.6 then
    if (ox == oy or abs(ox - oy) == 1) then
      return 1
    end
    return 0
  elseif value > 0.45 then
    if (ox == oy) then
      return 0
    end
    return 1    
  elseif value > 0.3 then
    if (ox == oy) then
      return 1
    end
    return 0    
  elseif value > 0.15 then
    if (ox == oy or abs(ox - oy) == 1) then
      return 0
    end
    return 1    
  elseif value > 0 then
    if (ox == 1 and oy == 1) then
      return 1
    end
    return 0
  end
  return 0
end