TIC-80 LZW graphics compression

lzw.tic

pixal="abcdefghijklmnop"

function compressLZW(input)
  local dictionary = {}
  local result = {}
  local dictSize = 256
  local p = ""

  for i = 0, 255 do
    dictionary[string.char(i)] = i
  end

  local inputLen = #input
  local i = 1

  while i <= inputLen do
    local c = input:sub(i, i)
    local pc = p .. c

    if dictionary[pc] then
      p = pc
    else
      table.insert(result, dictionary[p])
      dictionary[pc] = dictSize
      dictSize = dictSize + 1
      p = c
    end

    i = i + 1
  end

  if p ~= "" then
    table.insert(result, dictionary[p])
  end

  return result
end

function decompressLZW(input)
  local dictionary = {}
  local result = {}
  local dictSize = 256

  for i = 0, 255 do
    dictionary[i] = string.char(i)
  end

  local inputLen = #input
  local i = 1

  local p = dictionary[input[i]]
  table.insert(result, p)
  i = i + 1

  while i <= inputLen do
    local code = input[i]
    local entry

    if dictionary[code] then
      entry = dictionary[code]
    elseif code == dictSize then
      entry = p .. p:sub(1, 1)
    else
      return nil, "Invalid compressed data"
    end

    table.insert(result, entry)

    dictionary[dictSize] = p .. entry:sub(1, 1)
    dictSize = dictSize + 1

    p = entry

    i = i + 1
  end

  return table.concat(result)
end

function sget(x,y)
    local addr=0x4000+(x//8+y//8*16)*32
    return peek4(addr*2+x%8+y%8*8)
end

function sput(x,y,c)
    local addr=0x4000+(x//8+y//8*16)*32
    return poke4(addr*2+x%8+y%8*8,c)
end


-- Test the compress and decompress functions

local input = ""

for y = 0, 256 do
	for x = 0, 128 do
		local c = sget(x,y)
		c=math.floor(c)
		input = input .. string.sub(pixal,c,c)
	end
end

trace("Input len: "..#input,0,0)

local compressed = compressLZW(input)
trace("Compressed len: " .. #compressed,0,7)


# compressed data
# local gfxdata = {54,256,257,258,259,54,... etc.

local compressed = gfxdata
local decompressed = decompressLZW(compressed)

function decomp()
--	print("please wait, LZW decompressing")

	local i = 1
	for y=0,255 do
		for x=0,128 do
			local cc = string.sub(decompressed,i,i)
			local c = 15
			if cc == "0" then
				c = 0
			end
			if cc == "1" then
				c = 1
			end
			if cc == "2" then
				c = 2
			end
			if cc == "3" then
				c = 3
			end
			if cc == "4" then
				c = 4
			end
			if cc == "5" then
				c = 5
			end
			if cc == "6" then
				c = 6
			end
			if cc == "7" then
				c = 7
			end
			if cc == "8" then
				c = 8
			end
			if cc == "9" then
				c = 9
			end
			if cc == "A" then
				c = 10
			end
			if cc == "B" then
				c = 11
			end
			if cc == "C" then
				c = 12
			end
			if cc == "D" then
				c = 13
			end
			if cc == "E" then
				c = 14
			end
			if cc == "F" then
				c = 15
			end
						
			sput(x,y,c)
			i = i + 1
		end
	end
end

trace("Decompressed len: " .. #decompressed .. "",0,14)
trace(string.format("Size diff: %.2f", 100-((#compressed)/(#input)*100)) .. "%",0,22)
trace("compressed data: '" .. table.concat(compressed, ",") .. "'")