Menus

local w,h = term.getSize()
local select = 1

--Some draw functions to get us started

local function printCentered(str, ypos)
  term.setCursorPos(w/2 - #str/2, ypos)
  term.write(str)
end

local function printRight(str, ypos)
  term.setCursorPos(w - #str, ypos)
  term.write(str)
end

--Add the menus here

function drawMain()
  printCentered("Picture 1", 8)
  printCentered("Picture 2", 12)
  printCentered("Quit", h-2)

  local ypos = 9
  if select == 2 then ypos = 13
  elseif select == 3 then ypos = h-1 end
  printCentered("---------", ypos)
end

function drawPicOne()
  local rookList = {
		"|'-'-'| ",
		" \\   / ",
		"  |   |  ",
		"  |   |  ",
		"  |   |  ",
		"  |   |  ",
		"  |___|  ",
		" /_____\\ ",
		"(_______)"
	}

	for i=1,#rookList do
		printCentered(rookList[i], 3 + i)
	end

	printCentered("Picture 2", h-4)
	printCentered("Back", h-1)
	local ypos = h-3;
	if select == 2 then ypos = h end
	printCentered("---------", ypos)
end

function drawPicTwo()
  local bishopList = {
		"   _<>  ",
	    " /\\\\  \\",
		" \\ \\) /",
	   "  \\__/  ",
		" (____) ",
		"  |  |  ",
		"  |  |  ",
		"  |  |  ",
		"  |__|  ",
		" /____\\ ",
		"(______)"
	}

	for i=1,#bishopList do
		printCentered(bishopList[i], 2 + i)
	end

	printCentered("Picture 1", h-4)
	printCentered("Back", h-1)
	local ypos = h-3;
	if select == 2 then ypos = h end
	printCentered("---------", ypos)
end

function drawHeader()
  printCentered("PICTURE VIEWER", 1)
  printCentered(string.rep("-", w), 2)
  printRight("by nitrofingers", h)
end

--Menu state

local menustate = "main"

local mopt = {
  ["main"] = {
    options = {"pic1", "pic2", "quit"},
    draw = drawMain
  },
  ["pic1"] = {
    options = {"pic2", "main"},
	draw = drawPicOne
  },
  ["pic2"] = {
    options = {"pic1", "main"},
	draw = drawPicTwo
  }
}

--Run Function

function runMenu()
  while true do
    term.clear()
    drawHeader()
    mopt[menustate].draw()

    local id, key = os.pullEvent("key")
    --UP = 200, DOWN = 208, ENTER = 28

    if key == 200 and select > 1 then select = select-1
    elseif key == 208 and select < #mopt[menustate].options then select = select+1
    elseif key == 28 then
      if mopt[menustate].options[select] == "quit" then break end
      menustate = mopt[menustate].options[select]
    end
  end
end

runMenu()
term.clear()
term.setCursorPos(1,1)