Simple program for displaying BIMG files on a term capable peripheral

billboard.lua

local function resetPalette(periph)
  local mon
  if periph == "term" then
    mon = term
  else
    mon = assert(peripheral.wrap(periph), periph.." is not a valid peripheral")
  end

  for i = 0, 15 do
    mon.setPaletteColor(2^i, term.nativePaletteColor(2^i))
  end
end

local function main(periph, filename)
  if not (periph and filename) then
    print("usage: peripheral filename\nOr peripheral reset")
    return
  end
  
  local mon
  if periph == "term" then
    mon = term
  else
    mon = assert(peripheral.wrap(periph), periph.." is not a valid peripheral")
    mon.setTextScale(0.5)
  end
  if filename == "reset" then
    resetPalette(periph)
    return
  end
  local imfile = filename
  assert(fs.exists(imfile), imfile.." does not exist")
  assert(not fs.isDir(imfile), imfile.." is a directory")
  local f = assert(fs.open(imfile, "rb"))
  local im = assert(textutils.unserialize(f.readAll()), imfile.." is not a valid BIMG file")
  f.close()
  
  mon.clear()

  local doLoop = true

  while doLoop do
    doLoop = #im > 1 or im.animation or im.animated
    -- setup initial palette
    if im.palette then
      for k,v in pairs(im.palette) do
        mon.setPaletteColor(2^k, table.unpack(v))
      end
    end
    for _, frame in ipairs(im) do
      if frame.palette then
        for k,v in pairs(frame.palette) do
          mon.setPaletteColor(2^k, table.unpack(v))
        end
      end
      for yPos,v in pairs(frame) do
        if type(yPos) == "number" then
          mon.setCursorPos(1,yPos)
          mon.blit(table.unpack(v))
        end
      end
      local timer = os.startTimer(im.secondsPerFrame or 0.05)
      repeat
        local event = {os.pullEventRaw()}
        if event[1] == "terminate" then
          resetPalette(periph)
          return
        end
      until event[1] == "timer" and event[2] == timer
    end
  end
end

main(...)