bmp24.lua

--saves a 24 bit uncompressed bmp based
--on a 2d table of {r,g,b} indices
--(each channel's value should be no
--more than 255, of course)
function bmp24(map,path)
  --parse parameters:
  if type(map) ~= 'table' then
    return nil,'Map parameter is not table'
  end
  if path and type(path) ~= 'string' then
    return nil,'Path parameter exists, but is not string'
  end
  path=path or '/'..shell.dir()..'/untitled.bmp'
  --idiot check to see if rows are same len:
  local idiot=false
  local temp=0
  local temp2=math.huge
  for iy,mr in ipairs(map) do
    if #mr > temp then temp=#mr end
    if temp2 < temp then
      idiot=true break end
    temp2=#mr
  end
  if idiot then --if idiot then add magenta to missing columns
    for iy,mr in ipairs(map) do
      while #mr < temp do
        mr[#mr+1]={255,0,255}
      end
    end
  end
  --open file and write header
  local function littleEnd(num)
    if num==0 then return {'00'} end
    local bEnd=string.format("%x",num)
    if #bEnd%2 == 1 then bEnd='0'..bEnd end
    local lEnd={}
    for i=1,#bEnd,2 do lEnd[#lEnd+1]=bEnd:sub(i,i+1) end
    local fl=0
    for i=1,math.floor(#lEnd/2) do
      fl=#lEnd-i+1
      lEnd[i],lEnd[fl]=lEnd[fl],lEnd[i]
    end
    return lEnd
  end
  local function fillTab(tab,to)
    while #tab < to do tab[#tab+1]='00' end
    return tab
  end
  local file=io.open(path,'wb')
   --file signature:2 bytes, big
  file:write(66)--"B"
  file:write(77)--"M"
  local rowPadding=(4-(3*#map[1])%4)%4 --wow i probably did that badly but i dont care
  local fileSize=54+(3*#map[1]*#map)+(rowPadding*#map)
   --file size: 4 bytes, little
  for i,v in ipairs(fillTab(littleEnd(fileSize),4)) do--lol
    file:write(tonumber(v,16)) end
   --reserved: 4 bytes, doesn't matter it's just zero lol
  for i=1,4 do file:write(0) end
   --bitmap data offset: 4 bytes, little
  file:write(54)
  for i=1,3 do file:write(0) end
   --infoheader size: 4 bytes, little
  file:write(40)
  for i=1,3 do file:write(0) end
   --image width: 4 bytes, little
  for i,v in ipairs(fillTab(littleEnd(#map[1]),4)) do
    file:write(tonumber(v,16)) end
   --image height: 4 bytes, little
  for i,v in ipairs(fillTab(littleEnd(#map),4)) do
    file:write(tonumber(v,16)) end
   --number of planes: 2 bytes, little
  file:write(1)
  file:write(0)
   --number of bits per pixel: 2 bytes, little
  file:write(24)
  file:write(0)
   --compression type: 4 bytes, little
   --compressed image size: 4 bytes, little
   --x pixels per meter: 4 bytes, little
   --y pixels per meter: 4 bytes, little
   --used colors:4 bytes, little
   --important colors: 4 bytes, little
  for i=1,24 do file:write(0) end
  --write pixel data
  for iy=#map,1,-1 do
    for ix=1,#map[iy] do
      for ic=3,1,-1 do
        file:write(map[iy][ix][ic])
      end
    end
    if rowPadding > 0 then
      for i=1,rowPadding do
        file:write(0)
      end
    end
  end
  file:close()
  return true --it's finally over
end
--hopefully the below line works with require if uncommented
--return bmp24
--[[
--i used below for testing
local bmap={}
local count=255
local op=-1
local res={16,16}
for iy=1,res[2] do
  bmap[#bmap+1]={}
  for ix=1,res[1] do
    bmap[iy][#bmap[iy]+1]={count,count,count}
    count=count+op
  end
  --this line tests the uneven rows failsafe
  if iy==res[2] then bmap[iy][#bmap[iy]+1]={255,0,0} end
  bmap[#bmap+1]=row
end
bmp24(bmap)
--]]