My window API is laggy

local tHex = {
  ['0'] = colors.white,
  ['1'] = colors.orange,
  ['2'] = colors.magenta,
  ['3'] = colors.lightBlue,
  ['4'] = colors.yellow,
  ['5'] = colors.lime,
  ['6'] = colors.pink,
  ['7'] = colors.gray,
  ['8'] = colors.lightGray,
  ['9'] = colors.cyan,
  ['a'] = colors.purple,
  ['b'] = colors.blue,
  ['c'] = colors.brown,
  ['d'] = colors.green,
  ['e'] = colors.red,
  ['f'] = colors.black,
}
function create( parent, mx, my, l, h, color)
  if parent == term then
   parent = term.current()
  end
  mx = mx-1
  local e = {parent.getSize()}
  if l+mx > e[1] then
	l = e[1]-mx+1
  end
  if h+my > e[2] then
	h = e[2]-my+1
  end
  e = nil
  local parent = parent
  local focusedLine = h
  local x, y = 2, 1
  local Cx, Cy = mx, my-1
  local tc, bgc = colors.white, colors.black
  local c = color and term.isColor()
  local bgcl, tcl, t = {}, {}, {}
  local blinking, visible = false,true
  blit = function(text, myTc, myBgc)
   for i = 0, #text do
	  local char=string.sub(text,i,i)
	  if char == '\n' then
		y = y+1
		if y>h then
		  y = h
		  focusedLine = focusedLine+1
		  if not t[y+focusedLine] then
			t[y+focusedLine] = {}
			bgcl[y+focusedLine] = {}
			tcl[y+focusedLine] = {}
			for i2 = 1, l do
			  t[y+focusedLine][i2] = ' '
			  bgcl[y+focusedLine][i2] = bgc
			  tcl[y+focusedLine][i2]=tc
			end
		  end
		end
		x = 1
	  else
		if char ~= '' then
		  tcl[y+focusedLine][x-1] = tHex[string.sub(myTc, i, i)]
		  bgcl[y+focusedLine][x-1] = tHex[string.sub(myBgc, i, i)]
		  t[y+focusedLine][x-1] = char
		  x = x+1
		end
	  end
	end
	if visible then update() end
  end
  local hex = function(color)
	local val = "e"
	for k, v in pairs(tHex) do
	  if v == color then val = k end
	end
	return val
  end
  update = function()
	parent.setCursorBlink(false)
	for i = 1, h do
	  local text = ""
	  local textc = ""
	  local textbg = ""
	  for i2 = 1, l do
		textc = textc..hex(tcl[i+focusedLine][i2] or tc)
		textbg = textbg..hex(bgcl[i+focusedLine][i2] or bgc)
		if t[i+focusedLine][i2] == '' then
		 t[i+focusedLine][i2] = " "
		end
		text = text..(t[i+focusedLine][i2] or " ")
	  end
	  parent.setCursorPos(Cx+1, Cy +i)
	  parent.blit(text, textc, textbg)
	end
	parent.setCursorPos(x-1, y)
	parent.setCursorBlink(blinking)
  end
  for i = 1, h+focusedLine do
	t[i] = {}
	bgcl[i] = {}
	tcl[i] = {}
	for i2 = 1,l do
	  t[i][i2]=' '
	  bgcl[i][i2]=bgc
	  tcl[i][i2]=tc
	end
  end
  local invalidC = function()
	if not c then
	  printError('Exception reached at NyanOS.luac.term')
	  os.pullEvent('mouse_click')
	  os.reboot()
	end
  end
  local function colorStatus()
	return c
  end
  return {
	term.native,
	term.current,
	isColor = colorStatus,
	isColour = colorStatus,
	getSize = function()
	  return l, h
	end,
	getCursorPos = function()
	  return x, y
	end,
	getBackgroundColour = function()
	  return bgc
	end,
	getBackgroundColor = function()
	  return bgc
	end,
	getTextColour = function()
	  return tc
	end,
	getTextColor = function()
	  return tc
	end,
	write = function(text)
	  text  = tostring(text)
	  if (not text) or text == '' then
		return
	  end
	  blit(
		text,
		hex(tc):rep(#text),
		hex(bgc):rep(#text)
	  )
	end,
	setCursorPos = function(cx, cy)
	  x = cx+1
	  y = cy
	  if visible then update() end
	end,
	setTextColor = function(k)
	  tc = k
	  invalidC()
	end,
	setBackgroundColor = function(k)
	   bgc = k
	   invalidC()
	end,
	 setTextColour = function(k)
	   tc = k
	   invalidC()
	end,
	setBackgroundColour = function(k)
	   bgc = k
	   invalidC()
	end,
	scroll = function(scr)
	  focusedLine = focusedLine+scr
	  for i2 = 0, focusedLine+h do
		if not t[i2+h] then
		 t[y+i2] = {}
		 bgcl[y+i2] = {}
		 tcl[y+i2] = {}
		 for i = 1, l do
		 t[h+i2][i]=' '
		 bgcl[h+i2][i]=bgc
		 tcl[h+i2][i]=tc
		 end
	   end
	 end
	  if visible then update() end
	end,
	clear = function(color)
	  for i = 1, #t do
		t[i] = {}
		bgcl[i] = {}
		tcl[i] = {}
		for i2 = 1,l do
		  t[i][i2]=' '
		  bgcl[i][i2]=color or bgc
		  tcl[i][i2]=tc
		end
	  end
	  if visible then update() end
	end,
	clearLine = function(myY, color)
	  if not myY then
	   myY = y
	  end
	  y = myY
	  t[y+focusedLine] = {}
	  bgcl[y+focusedLine] = {}
	  tcl[y+focusedLine] = {}
	  for i = 1, l do
		t[y+focusedLine][i]=' '
		bgcl[y+focusedLine][i]=color or bgc
		tcl[y+focusedLine][i]=tc
	  end
	  if visible then update() end
	end,
	setCursorBlink = function(bool)
	  blinking = bool
	  if visible then update() end
	end,
	setVisible = function(bool)
	  visible = bool
	  if bool then
	   update()
	  else
	   parent.setCursorBlink(false)
	  end
	end,
	blit = blit,
  }
end
local l, h = term.getSize()
M = create(term.native(), 1, 1, l, h, true)
term.redirect(M)
shell.run('rom/programs/shell')