LIKOGif.lua

--A special gif library for LIKO-12
--Written by Rami Sabbagh (RamiLego4Game)

--Source: http://www.matthewflickinger.com/lab/whatsinagif/bits_and_bytes.asp

--Arguments: filename, width, height, 16 color palette

local args = {...}
local gif = {}
local bit = require("bit")

local zero = string.char(0)

--Helping function
local function bytes(b,len)
  if #b >= len then return b:sub(1,len) end
  return b..string.rep(zero,len-#b)
end

local function indian(str,len)
  if len then str = bytes(str,len) end
  local bytes = {}
  local counter = #str
  for char in string.gmatch(".",str) do
    bytes[counter] = char
    counter = counter-1
  end
  return table.concat(bytes)
end

local function tobytes(num,len)
  local str = ""
  while true do
    local byte = bit.band(num,255)
    num = bit.rshift(num,8)
    str = str..string.char(byte)
    if num == 0 then break end
  end
  return indian(str,len)
end

--It's better to use local variables for speed.
local filename = args[1] or "NULL"
local file = love.filesystem.newFile(filename,"w")

--Header
file:write("GIF87a",6)

--Logical Screen Descriptor
local LSD = ""
local width = args[2] or 192
local height = args[3] or 128
LSD = LSD..tobytes(width,2)..tobytes(height,2)
LSD = LSD..tobytes(tonumber(10110011,2),1) --Packed Byte, configured for 16 color, 4bits index
LSD = LSD..tobytes(0,1) --Background color index
LSD = LSD..tobytes(0,1) --Pixel aspect ratio

file:write(LSD,7)

--Global Color Table
local palette = args[4]
local paletteBytes = {}

for k,v in ipairs(palette) do
  table.insert(paletteBytes, tobytes(v[1],1)..tobytes(v[2],1)..tobytes(v[3],1))
end

file:write(table.concat(paletteBytes),48)

--Static Image Descriptor
--No local palette:
local ImgDescBase = tobytes(0x2C,1) .. tobytes(0x0000,2) .. tobytes(0x0000,2) .. tobytes(width,2) .. tobytes(height,2)
local ImgDesc = ImgDescBase .. string.char(tonumber(00000000,2))

--With local palette:
local ImgDescLocal = ImgDescBase .. string.char(tonumber(10000011,2))

--Special Variables
local localpalette
local rawbase = {}
for i=1, width*height do table.insert(rawbase,zero) end

function gif.setPalette(p)
  local flag = false
  for k,v in ipairs(p) do
    for k2,v2 in ipairs(v) do
      if v2 ~= palette[k][k2] then
        flag = true
        break
      end
    end
    if flag then break end
  end

  if not flag then localpalette = false end

  local pbytes = {}
  for k,v in ipairs(p) do
    table.insert(pbytes, tobytes(v[1],1)..tobytes(v[2],1)..tobytes(v[3],1))
  end

  localpalette = table.concat(pbytes)
end

local tconcat = table.concat
local unpack = unpack

function gif.frame(frame)
  --Image Descriptor
  if localpalette then
    file:write(ImgDescLocal,10)
    file:write(localpalette)
  else
    file:write(ImgDesc,10)
  end

  local rawdata = {unpack(rawbase)} --A trick to make the table with premade hash
  local counter = 1

  frame:mapPixel(function(x,y,r,g,b,a)
    rawdata[counter] = r
    counter = counter + 1
    return r,g,b,a
  end)

  rawdata = tconcat(rawdata)

  --LZW Compression

end

function gif.close()

end

return gif